--- /dev/null
+. $Cambridge: exim/doc/doc-src/spec.src,v 1.1 2004/10/07 15:04:35 ph10 Exp $
+.
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+
+.index @$1, @$2, etc. $it{see numerical variables}
+.index address||rewriting $it{see rewriting}
+.index CR character $it{see carriage return}
+.index CRL $it{see certificate revocation list}
+.index delivery||failure report $it{see bounce message}
+.index dialup $it{see intermittently connected hosts}
+.index failover $it{see fallback}
+.index fallover $it{see fallback}
+.index filter||Sieve $it{see Sieve filter}
+.index ident $it{see RFC 1413}
+.index LF character $it{see linefeed}
+.index maximum $it{see limit}
+.index NUL $it{see binary zero}
+.index process id $it{see pid}
+.index RBL $it{see DNS list}
+.index redirection $it{see address redirection}
+.index return path||$it{see also envelope sender}
+.index SSL $it{see TLS}
+.index string||expansion $it{see expansion}
+.index top bit $it{see 8-bit characters}
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+. ======================================================
+
+.push
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+.space 8ld
+$chead{University of Cambridge Computing Service}
+.space 2ld
+$chead{Specification of the Exim Mail Transfer Agent}
+.space 3ld
+by
+.space 1ld
+Philip Hazel
+.space ~~sys.leftonpage - 15*~~sys.linedepth
+.justify left
+University Computing Service
+New Museums Site
+Pembroke Street
+Cambridge CB2 3QH
+United Kingdom
+.blank
+.tabs 6
+$it{phone:} $t +44 1223 334600
+$it{fax:} $t +44 1223 334679
+$it{email:} $t ph10 $it{at} cus.cam.ac.uk
+.blank
+Edition for Exim ~~version, ~~versionmonth ~~versionyear
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+
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+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Introduction
+.set runningfoot "introduction"
+
+.if ~~sys.fancy
+$c$bi{If I have seen further it is by standing on the shoulders of giants.}##(Isaac Newton)
+.elif !~~html
+$c"If I have seen further it is by standing on the shoulders of giants."
+.newline
+$e (Isaac Newton)
+.else
+\*If I have seen further it is by standing on the shoulders of giants.*\
+(Isaac Newton).
+.fi
+.blank 4
+
+Exim is a mail transfer agent (MTA) for hosts that are running Unix or
+Unix-like operating systems. It was designed on the assumption that it would be
+run on hosts that are permanently connected to the Internet. However, it can be
+used on intermittently connected hosts with suitable configuration adjustments.
+
+Configuration files currently exist for the following operating systems: AIX,
+BSD/OS (aka BSDI), Darwin (Mac OS X), DGUX, FreeBSD, GNU/Hurd, GNU/Linux,
+HI-OSF (Hitachi), HP-UX, IRIX, MIPS RISCOS, NetBSD, OpenBSD, QNX, SCO, SCO
+SVR4.2 (aka UNIX-SV), Solaris (aka SunOS5), SunOS4, Tru64-Unix (formerly
+Digital UNIX, formerly DEC-OSF1), Ultrix, and Unixware. Some of these operating
+systems are no longer current and cannot easily be tested, so the configuration
+files may no longer work in practice.
+
+There are also configuration files for compiling Exim in the Cygwin environment
+that can be installed on systems running Windows. However, this document does
+not contain any information about running Exim in the Cygwin environment.
+
+The terms and conditions for the use and distribution of Exim are contained in
+the file \(NOTICE)\. Exim is distributed under the terms of the GNU General
+Public Licence, a copy of which may be found in the file \(LICENCE)\.
+
+The use, supply or promotion of Exim for the purpose of sending bulk,
+unsolicited electronic mail is incompatible with the basic aims of the program,
+which revolve around the free provision of a service that enhances the quality
+of personal communications. The author of Exim regards indiscriminate
+mass-mailing as an antisocial, irresponsible abuse of the Internet.
+
+Exim owes a great deal to Smail 3 and its author, Ron Karr. Without the
+experience of running and working on the Smail 3 code, I could never have
+contemplated starting to write a new MTA. Many of the ideas and user interfaces
+were originally taken from Smail 3, though the actual code of Exim is entirely
+new, and has developed far beyond the initial concept.
+
+Many people, both in Cambridge and around the world, have contributed to the
+development and the testing of Exim, and to porting it to various operating
+systems. I am grateful to them all. The distribution now contains a file called
+\(ACKNOWLEDGMENTS)\, in which I have started recording the names of
+contributors.
+
+.section Exim documentation
+.index documentation
+.em
+This edition of the Exim specification applies to version ~~version of Exim.
+Substantive changes from the ~~previousversion edition are marked by bars in
+the right-hand margin in the PostScript, PDF, and plain text versions of the
+document, and by green text in the HTML version, as shown by this paragraph.
+Changes are not marked in the Texinfo version, because Texinfo doesn't support
+change bars. Minor corrections and rewordings are not marked.
+.nem
+
+This document is very much a reference manual; it is not a tutorial. The reader
+is expected to have some familiarity with the SMTP mail transfer protocol and
+with general Unix system administration. Although there are some discussions
+and examples in places, the information is mostly organized in a way that makes
+it easy to look up, rather than in a natural order for sequential reading.
+Furthermore, the manual aims to cover every aspect of Exim in detail, including
+a number of rarely-used, special-purpose features that are unlikely to be of
+very wide interest.
+
+.index books about Exim
+An `easier' discussion of Exim which provides more in-depth explanatory,
+introductory, and tutorial material can be found in a book entitled
+.if ~~html
+[(A HREF="http://www.uit.co.uk/exim-book/")]
+$it{The Exim SMTP Mail Server},
+[(/A)]
+published by UIT Cambridge.
+.else
+$it{The Exim SMTP Mail Server}, published by UIT Cambridge
+(\?http://www.uit.co.uk/exim-book/?\).
+.fi
+
+This book also contains a chapter that gives a general introduction to SMTP and
+Internet mail. Inevitably, however, the book is unlikely to be fully up-to-date
+with the latest release of Exim. (Note that the earlier book about Exim,
+published by O'Reilly, covers Exim 3, and many things have changed in Exim 4.)
+
+.index \(doc/NewStuff)\
+.index \(doc/ChangeLog)\
+.index change log
+As the program develops, there may be features in newer versions that have not
+yet made it into this document, which is updated only when the most significant
+digit of the fractional part of the version number changes. However,
+specifications of new features that are not yet in this manual are placed in
+the file \(doc/NewStuff)\ in the Exim distribution. All changes to the program
+(whether new features, bug fixes, or other kinds of change) are noted briefly
+in the file called \(doc/ChangeLog)\.
+
+.index \(doc/spec.txt)\
+This specification itself is available as an ASCII file in \(doc/spec.txt)\ so
+that it can easily be searched with a text editor. Other files in the \(doc)\
+directory are:
+.display rm
+.tabs 18
+\(OptionLists.txt)\ $t $rm{list of all options in alphabetical order}
+\(dbm.discuss.txt)\ $t $rm{discussion about DBM libraries}
+\(exim.8)\ $t $rm{a man page of Exim's command line options}
+\(filter.txt)\ $t $rm{specification of the filter language}
+\(pcrepattern.txt)\ $t $rm{specification of PCRE regular expressions}
+\(pcretest.txt)\ $t $rm{specification of the PCRE testing program}
+\(Exim3.upgrade)\ $t $rm{upgrade notes from release 2 to release 3}
+\(Exim4.upgrade)\ $t $rm{upgrade notes from release 3 to release 4}
+.endd
+The main specification and the specification of the filtering language are also
+available in other formats (HTML, PostScript, PDF, and Texinfo). Section
+~~SECTavail below tells you how to get hold of these.
+
+
+.section FTP and web sites, and mailing list
+.index web site
+.index FTP site
+The primary distribution site for Exim is an FTP site, whose contents are
+described in \*Where to find the Exim distribution*\ below. In addition,
+there is a web site at \?http://www.exim.org?\ by courtesy of Energis Squared,
+formerly Planet Online Ltd, who are situated in the UK. The site is mirrored in
+a number of other countries; links to the mirrors are listed on the home page.
+The web site contains the Exim distribution, and you can also find the
+documentation and the
+.index FAQ
+.if ~~html
+[(A HREF="FAQ.html")]
+.fi
+FAQ
+.if ~~html
+[(/A)]
+.fi
+online there, as well as other relevant material.
+
+.index mailing lists||for Exim users
+Energis Squared also provide resources for the following mailing lists:
+.display rm
+.tabs 28
+$it{exim-users@@exim.org} $t general discussion list
+$it{exim-announce@@exim.org} $t moderated, low volume announcements list
+.endd
+You can subscribe to these lists, change your existing subscriptions, and view
+or search the archives via the
+.if ~~html
+[(A HREF="http://www.exim.org/maillist.html")]
+.fi
+mailing lists
+.if ~~html
+[(/A)]
+.fi
+link on the Exim home page. The $it{exim-users} mailing list is also forwarded
+to \?http://www.egroups.com/list/exim-users?\, an archiving system with
+searching capabilities.
+
+.section Exim training
+.index training courses
+From time to time (approximately annually at the time of writing),
+lecture-based training courses are run by the author of Exim in Cambridge, UK.
+Details can be found on the web site
+.if ~~html
+[(A HREF="http://www-tus.csx.cam.ac.uk/courses/exim/")]
+.fi
+\?http://www-tus@.csx@.cam@.ac.uk/courses/exim/?\.
+.if ~~html
+[(/A)]
+.fi
+
+.section Bug reports
+.index bug reports
+.index reporting bugs
+Reports of obvious bugs should be emailed to \*bugs@@exim.org*\. However, if
+you are unsure whether some behaviour is a bug or not, the best thing to do is
+to post a message to the $it{exim-users} mailing list and have it discussed.
+
+
+.section Where to find the Exim distribution
+.rset SECTavail "~~chapter.~~section"
+.index FTP site
+.index distribution||ftp site
+The master ftp site for the Exim distribution is
+.display rm
+.if ! ~~sys.fancy
+.indent 0
+.fi
+\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim?\
+.endd
+Within that directory there are subdirectories called \(exim3)\ (for previous
+Exim 3 distributions), \(exim4)\ (for the latest Exim 4 distributions), and
+\(Testing)\ for occasional testing versions. Those mirror sites that I know
+about are listed in the file
+.display rm
+.if ! ~~sys.fancy
+.indent 0
+.fi
+\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/Mirrors?\
+.endd
+In the \(exim4)\ subdirectory, the current release can always be found in
+files called
+.display rm
+\(exim-$it{n.nn}.tar.gz)\
+\(exim-$it{n.nn}.tar.bz2)\
+.endd
+where $it{n.nn} is the highest such version number in the directory. The two
+files contain identical data; the only difference is the type of compression.
+The \(.bz2)\ file is usually a lot smaller than the \(.gz)\ file.
+.index distribution||signing details
+.index distribution||public key
+.index public key for signed distribution
+The distributions are signed with Philip Hazel's GPG key.
+The corresponding public key is available from a number of keyservers, and
+there is also a copy in the file:
+.display rm
+.if ! ~~sys.fancy
+.indent 0
+.fi
+\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/Public-Key?\
+.endd
+The signatures for the tar bundles are in:
+.display rm
+\(exim-$it{n.nn}.tar.gz.sig)\
+\(exim-$it{n.nn}.tar.bz2.sig)\
+.endd
+
+When there is only a small amount of change from one release to the next, a
+patch file may be provided, with a final component name of the form
+.display rm
+\(exim-patch-$it{n.nn}-$it{m.mm}.gz)\
+.endd
+For each released version, the log of changes is made separately available in
+the directory
+.display rm
+\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/ChangeLogs?\
+.endd
+so that it is possible to find out what has changed without having to download
+the entire distribution.
+
+.index documentation||available formats
+The main distribution contains ASCII versions of this specification and other
+documentation; other formats of the documents are available in separate files
+inside the \(exim4)\ directory of the FTP site:
+.display rm
+\(exim-html-$it{n.nn}.tar.gz)\
+\(exim-pdf-$it{n.nn}.tar.gz)\
+\(exim-postscript-$it{n.nn}.tar.gz)\
+\(exim-texinfo-$it{n.nn}.tar.gz)\
+.endd
+These tar files contain only the \(doc)\ directory, not the complete
+distribution, and are also available in \(.bz2)\ as well as \(.gz)\ forms.
+
+.index FAQ
+The FAQ is available for downloading in two different formats from
+.display rm
+.if ! ~~sys.fancy
+.indent 0
+.fi
+\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/exim4/FAQ.txt.gz?\
+\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/exim4/FAQ.html.tar.gz?\
+.endd
+The first of these is a single ASCII file that can be searched with a text
+editor. The second is a directory of HTML files, normally accessed by starting
+at \(index.html)\. The HTML version of the FAQ (which is also included in the
+HTML documentation tarbundle) includes a keyword-in-context index, which is
+often the most convenient way of finding your way around.
+
+.section Wish list
+.index wish list
+A wish list is maintained, containing ideas for new features that have been
+submitted. From time to time the file is exported to the ftp site:
+.display rm
+\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/exim4/WishList?\
+.endd
+Items are removed from the list if they get implemented.
+
+
+.section Contributed material
+.index contributed material
+At the ftp site, there is a directory called
+.display rm
+.if ! ~~sys.fancy
+.indent 0
+.fi
+\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/exim4/Contrib/?\
+.endd
+which contains miscellaneous files contributed to the Exim community by Exim
+users. There is also a collection of contributed configuration examples in
+.display rm
+.if ! ~~sys.fancy
+.indent 0
+.fi
+\?ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/exim4/config.samples.tar.gz?\
+.endd
+These samples are referenced from the FAQ.
+
+
+.section Limitations
+.index limitations of Exim
+.numberpars $.
+Exim is designed for use as an Internet MTA, and therefore handles addresses
+in RFC 2822 domain format only.
+.index bang paths||not handled by Exim
+It cannot handle UUCP `bang paths', though simple two-component bang paths can
+be converted by a straightforward rewriting configuration. This restriction
+does not prevent Exim from being interfaced to UUCP as a transport mechanism,
+provided that domain addresses are used.
+.nextp
+.index domainless addresses
+.index address||without domain
+Exim insists that every address it handles has a domain attached. For incoming
+local messages, domainless addresses are automatically qualified with a
+configured domain value. Configuration options specify from which remote
+systems unqualified addresses are acceptable. These are then qualified on
+arrival.
+.nextp
+.index transport||external
+.index external transports
+The only external transport currently implemented is an SMTP transport over a
+TCP/IP network (using sockets, including support for IPv6). However, a pipe
+transport is available, and there are facilities for writing messages to files
+and pipes, optionally in \*batched SMTP*\ format; these facilities can be used
+to send messages to some other transport mechanism such as UUCP, provided it
+can handle domain-style addresses. Batched SMTP input is also catered for.
+.nextp
+Exim is not designed for storing mail for dial-in hosts. When the volumes of
+such mail are large, it is better to get the messages `delivered' into files
+(that is, off Exim's queue) and subsequently passed on to the dial-in hosts by
+other means.
+.nextp
+Although Exim does have some facilities for scanning incoming messages, these
+are not comprehensive enough to do full virus or spam scanning. Such operations
+are best carried out using additional specialized software packages.
+.endp
+
+
+
+.section Run time configuration
+Exim's run time configuration is held in a single text file that is divided
+into a number of sections. The entries in this file consist of keywords and
+values, in the style of Smail 3 configuration files. A default configuration
+file which is suitable for simple online installations is provided in the
+distribution, and is described in chapter ~~CHAPdefconfil below.
+
+
+.section Calling interface
+.index Sendmail compatibility||command line interface
+Like many MTAs, Exim has adopted the Sendmail command line interface so that it
+can be a straight replacement for \(/usr/lib/sendmail)\ or
+\(/usr/sbin/sendmail)\ when sending mail, but you do not need to know anything
+about Sendmail in order to run Exim. For actions other than sending messages,
+Sendmail-compatible options also exist, but those that produce output (for
+example, \-bp-\, which lists the messages on the queue) do so in Exim's own
+format. There are also some additional options that are compatible with Smail
+3, and some further options that are new to Exim. Chapter ~~CHAPcommandline
+documents all Exim's command line options. This information is automatically
+made into the man page that forms part of the Exim distribution.
+
+Control of messages on the queue can be done via certain privileged command
+line options. There is also an optional monitor program called \*eximon*\, which
+displays current information in an X window, and which contains a menu
+interface to Exim's command line administration options.
+
+
+.section Terminology
+.index terminology definitions
+.index body of message||definition of
+The \*body*\ of a message is the actual data that the sender wants to transmit.
+It is the last part of a message, and is separated from the \*header*\ (see
+below) by a blank line.
+
+.index bounce message||definition of
+When a message cannot be delivered, it is normally returned to the sender in a
+delivery failure message. The term \*bounce*\ is commonly used for this action,
+and the error reports are often called \*bounce messages*\. This is a
+convenient shorthand for `delivery failure error report'. Such messages have an
+empty sender address in the message's \*envelope*\ (see below) to ensure that
+they cannot themselves give rise to further bounce messages.
+
+The term \*default*\ appears frequently in this manual. It is used to qualify a
+value which is used in the absence of any setting in the configuration. It may
+also qualify an action which is taken unless a configuration setting specifies
+otherwise.
+
+The term \*defer*\ is used when the delivery of a message to a specific
+destination cannot immediately take place for some reason (a remote host may be
+down, or a user's local mailbox may be full). Such deliveries are \*deferred*\
+until a later time.
+
+The word \*domain*\ is sometimes used to mean all but the first component of a
+host's name. It is $it{not} used in that sense here, where it normally
+refers to the part of an email address following the @@ sign.
+
+.index envelope, definition of
+.index sender||definition of
+A message in transit has an associated \*envelope*\, as well as a header and a
+body. The envelope contains a sender address (to which bounce messages should
+be delivered), and any number of recipient addresses. References to the
+sender or the recipients of a message usually mean the addresses in the
+envelope. An MTA uses these addresses for delivery, and for returning bounce
+messages, not the addresses that appear in the header lines.
+
+.index message||header, definition of
+.index header section||definition of
+The \*header*\ of a message is the first part of a message's text, consisting
+of a number of lines, each of which has a name such as ::From::, ::To::,
+::Subject::, etc. Long header lines can be split over several text lines by
+indenting the continuations. The header is separated from the body by a blank
+line.
+
+.index local part||definition of
+.index domain||definition of
+The term \*local part*\, which is taken from RFC 2822, is used to refer to that
+part of an email address that precedes the @@ sign. The part that follows the
+@@ sign is called the \*domain*\ or \*mail domain*\.
+
+.index local delivery||definition of
+.index remote delivery, definition of
+The terms \*local delivery*\ and \*remote delivery*\ are used to distinguish
+delivery to a file or a pipe on the local host from delivery by SMTP over
+TCP/IP to a remote host.
+
+.index return path||definition of
+\*Return path*\ is another name that is used for the sender address in a
+message's envelope.
+
+.index queue||definition of
+The term \*queue*\ is used to refer to the set of messages awaiting delivery,
+because this term is in widespread use in the context of MTAs. However, in
+Exim's case the reality is more like a pool than a queue, because there is
+normally no ordering of waiting messages.
+
+.index queue runner||definition of
+The term \*queue runner*\ is used to describe a process that scans the queue
+and attempts to deliver those messages whose retry times have come. This term
+is used by other MTAs, and also relates to the command \runq\, but in Exim
+the waiting messages are normally processed in an unpredictable order.
+
+.index spool directory||definition of
+The term \*spool directory*\ is used for a directory in which Exim keeps the
+messages on its queue -- that is, those that it is in the process of
+delivering. This should not be confused with the directory in which local
+mailboxes are stored, which is called a `spool directory' by some people. In
+the Exim documentation, `spool' is always used in the first sense.
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Incorporated code
+.set runningfoot "incorporated code"
+.index incorporated code
+.index regular expressions||library
+.index PCRE
+A number of pieces of external code are included in the Exim distribution.
+.numberpars $.
+Regular expressions are supported in the main Exim program and in the Exim
+monitor using the freely-distributable PCRE library, copyright (c) 2003
+University of Cambridge. The source is distributed in the directory
+\(src/pcre)\. However, this is a cut-down version of PCRE. If you want to use
+the PCRE library in other programs, you should obtain and install the full
+version from \?ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre?\.
+
+.space 1ld
+.nextp
+.index cdb||acknowledgement
+Support for the cdb (Constant DataBase) lookup method is provided by code
+contributed by Nigel Metheringham of Planet Online Ltd. which contains the
+following statements:
+.rule
+.push
+.if ~~sgcal
+.fontgroup 9
+.font 0
+.fi
+Copyright (c) 1998 Nigel Metheringham, Planet Online Ltd
+
+This program is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free Software
+Foundation; either version 2 of the License, or (at your option) any later
+version.
+
+This code implements Dan Bernstein's Constant DataBase (cdb) spec. Information,
+the spec and sample code for cdb can be obtained from
+\?http://www.pobox.com/@~djb/cdb.html?\. This implementation borrows some code
+from Dan Bernstein's implementation (which has no license restrictions applied
+to it).
+.newline
+.pop
+.rule
+The implementation is completely contained within the code of Exim.
+It does not link against an external cdb library.
+.space 1ld
+.nextp
+.index SPA authentication
+.index Samba project
+.index Microsoft Secure Password Authentication
+Client support for Microsoft's \*Secure Password Authentication*\ is provided
+by code contributed by Marc Prud'hommeaux. Server support was contributed by
+Tom Kistner. This includes code taken from the Samba project, which is released
+under the Gnu GPL.
+
+.space 1ld
+.nextp
+.index Cyrus
+.index \*pwcheck*\ daemon
+.index \*pwauthd*\ daemon
+Support for calling the Cyrus \*pwcheck*\ and \*saslauthd*\ daemons is provided
+by code taken from the Cyrus-SASL library and adapted by Alexander S.
+Sabourenkov. The permission notice appears below, in accordance with the
+conditions expressed therein.
+
+.rule
+.push
+.if ~~sgcal
+.fontgroup 9
+.font 0
+.fi
+Copyright (c) 2001 Carnegie Mellon University. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions
+are met:
+
+.if ~~sgcal
+.cancelflag $npbracket
+.flag $npbracket "" "."
+.fi
+.numberpars
+Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+.nextp
+Redistributions in binary form must reproduce the above copyright
+notice, this list of conditions and the following disclaimer in
+the documentation and/or other materials provided with the
+distribution.
+.nextp
+The name `Carnegie Mellon University' must not be used to
+endorse or promote products derived from this software without
+prior written permission. For permission or any other legal
+details, please contact
+.display rm
+Office of Technology Transfer
+Carnegie Mellon University
+5000 Forbes Avenue
+Pittsburgh, PA 15213-3890
+(412) 268-4387, fax: (412) 268-7395
+tech-transfer@@andrew.cmu.edu
+.endd
+.nextp
+Redistributions of any form whatsoever must retain the following
+acknowledgment:
+.newline
+.push
+.indent ~~sys.indent + 3em
+.justify left
+$it{This product includes software developed by Computing Services
+at Carnegie Mellon University (\?http://www.cmu.edu/computing/?\).}
+.newline
+.pop
+.endp
+.if ~~sgcal
+.cancelflag $npbracket
+.flag $npbracket "(" ")"
+.fi
+
+CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
+THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
+FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
+AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+.newline
+.pop
+.rule
+
+.space 1ld
+.nextp
+.index monitor
+.index X-windows
+.index Athena
+The Exim Monitor program, which is an X-Window application, includes
+modified versions of the Athena StripChart and TextPop widgets.
+This code is copyright by DEC and MIT, and their permission notice appears
+below, in accordance with the conditions expressed therein.
+
+.rule
+.push
+.if ~~sgcal
+.fontgroup 9
+.font 0
+.fi
+Copyright 1987, 1988 by Digital Equipment Corporation, Maynard, Massachusetts,
+and the Massachusetts Institute of Technology, Cambridge, Massachusetts.
+.blank
+$c All Rights Reserved
+.blank
+Permission to use, copy, modify, and distribute this software and its
+documentation for any purpose and without fee is hereby granted,
+provided that the above copyright notice appear in all copies and that
+both that copyright notice and this permission notice appear in
+supporting documentation, and that the names of Digital or MIT not be
+used in advertising or publicity pertaining to distribution of the
+software without specific, written prior permission.
+
+DIGITAL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
+ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL
+DIGITAL BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR
+ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
+WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
+ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
+SOFTWARE.
+.newline
+.pop
+.rule
+.endp
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter How Exim receives and delivers mail
+.set runningfoot "receiving & delivering mail"
+
+.section Overall philosophy
+.index design philosophy
+Exim is designed to work efficiently on systems that are permanently connected
+to the Internet and are handling a general mix of mail. In such circumstances,
+most messages can be delivered immediately. Consequently, Exim does not
+maintain independent queues of messages for specific domains or hosts, though
+it does try to send several messages in a single SMTP connection after a host
+has been down, and it also maintains per-host retry information.
+
+
+.section Policy control
+.index policy control||overview
+Policy controls are now an important feature of MTAs that are connected to the
+Internet. Perhaps their most important job is to stop MTAs being abused as
+`open relays' by misguided individuals who send out vast amounts of unsolicited
+junk, and want to disguise its source. Exim provides flexible facilities for
+specifying policy controls on incoming mail:
+.numberpars $.
+.index ~~ACL||introduction
+Exim 4 (unlike previous versions of Exim) implements policy controls on
+incoming SMTP mail by means of \*Access Control Lists*\ (ACLs). Each list is a
+series of statements that may either grant or deny access. ACLs can be used at
+several places in the SMTP dialogue while receiving a message. However, the
+most common places are after each \\RCPT\\ command, and at the very end of the
+message. The sysadmin can specify conditions for accepting or rejecting
+individual recipients or the entire message, respectively, at these two points
+(see chapter ~~CHAPACL). Denial of access results in an SMTP error code.
+.nextp
+An ACL is also available for locally generated, non-SMTP messages. In this
+case, the only available actions are to accept or deny the entire message.
+.nextp
+When a message has been received, either from a remote host or from the local
+host, but before the final acknowledgement has been sent, a locally supplied C
+function called \*local@_scan()*\ can be run to inspect the message and decide
+whether to accept it or not (see chapter ~~CHAPlocalscan). If the message is
+accepted, the list of recipients can be modified by the function.
+.nextp
+After a message has been accepted, a further checking mechanism is available in
+the form of the $it{system filter} (see chapter ~~CHAPsystemfilter). This runs
+at the start of every delivery process.
+.endp
+
+.section User filters
+.index filter||introduction
+.index Sieve filter
+In a conventional Exim configuration, users are able to run private filters by
+setting up appropriate \(.forward)\ files in their home directories. See
+chapter ~~CHAPredirect (about the \%redirect%\ router) for the configuration
+needed to support this, and the separate document entitled
+.if ~~html
+[(A HREF="filter_toc.html")]
+.fi
+\*Exim's interfaces to mail filtering*\
+.if ~~html
+[(/A)]
+.fi
+for user details. Two different kinds of filtering are available:
+.numberpars $.
+Sieve filters are written in the standard filtering language that is defined by
+RFC 3028.
+.nextp
+Exim filters are written in a syntax that is unique to Exim, but which is more
+powerful than Sieve, which it pre-dates.
+.endp
+User filters are run as part of the routing process, described below.
+
+
+.section Message identification
+.rset SECTmessiden "~~chapter.~~section"
+.index message||ids, details of format
+.index format||of message id
+.index id of message
+.index base62
+.index base36
+.index Darwin
+.index Cygwin
+Every message handled by Exim is given a \*message id*\ which is sixteen
+characters long. It is divided into three parts, separated by hyphens, for
+example \"16VDhn-0001bo-D3"\. Each part is a sequence of letters and digits,
+normally encoding numbers in base 62. However, in the Darwin operating
+system (Mac OS X) and when Exim is compiled to run under Cygwin, base 36
+(avoiding the use of lower case letters) is used instead, because the message
+id is used to construct file names, and the names of files in those systems are
+not case-sensitive.
+
+.index pid (process id)||re-use of
+The detail of the contents of the message id have changed as Exim has evolved.
+Earlier versions relied on the operating system not re-using a process id (pid)
+within one second. On modern operating systems, this assumption can no longer
+be made, so the algorithm had to be changed. To retain backward compatibility,
+the format of the message id was retained, which is why the following rules are
+somewhat eccentric:
+.numberpars $.
+The first six characters of the message id are the time at which the message
+started to be received, to a granularity of one second. That is, this field
+contains the number of seconds since the start of the epoch (the normal Unix
+way of representing the date and time of day).
+.nextp
+After the first hyphen, the next six characters are the id of the process that
+received the message.
+.nextp
+There are two different possibilities for the final two characters:
+.numberpars alpha
+.index \localhost@_number\
+If \localhost@_number\ is not set, this value is the fractional part of the
+time of reception, normally in units of 1/2000 of a second, but for systems
+that must use base 36 instead of base 62 (because of case-insensitive file
+systems), the units are 1/1000 of a second.
+.nextp
+If \localhost@_number\ is set, it is multiplied by 200 (100) and added to
+the fractional part of the time, which in this case is in units of 1/200
+(1/100) of a second.
+.endp
+.endp
+After a message has been received, Exim waits for the clock to tick at the
+appropriate resolution before proceeding, so that if another message is
+received by the same process, or by another process with the same (re-used)
+pid, it is guaranteed that the time will be different. In most cases, the clock
+will already have ticked while the message was being received.
+
+.section Receiving mail
+.index receiving mail
+.index message||reception
+The only way Exim can receive mail from a remote host is using SMTP over
+TCP/IP, in which case the sender and recipient addresses are tranferred using
+SMTP commands. However, from a locally running process (such as a user's MUA),
+there are several possibilities:
+.numberpars $.
+If the process runs Exim with the \-bm-\ option, the message is read
+non-interactively (usually via a pipe), with the recipients taken from the
+command line, or from the body of the message if \-t-\ is also used.
+.nextp
+If the process runs Exim with the \-bS-\ option, the message is also read
+non-interactively, but in this case the recipients are listed at the start of
+the message in a series of SMTP \\RCPT\\ commands, terminated by a \\DATA\\
+command. This is so-called `batch SMTP' format,
+but it isn't really SMTP. The SMTP commands are just another way of passing
+envelope addresses in a non-interactive submission.
+.nextp
+If the process runs Exim with the \-bs-\ option, the message is read
+interactively, using the SMTP protocol. A two-way pipe is normally used for
+passing data between the local process and the Exim process.
+This is `real' SMTP and is handled in the same way as SMTP over TCP/IP. For
+example, the ACLs for SMTP commands are used for this form of submission.
+.nextp
+A local process may also make a TCP/IP call to the host's loopback address
+(127.0.0.1) or any other of its IP addresses. When receiving messages, Exim
+does not treat the loopback address specially. It treats all such connections
+in the same way as connections from other hosts.
+.endp
+
+.index message||sender, constructed by Exim
+.index sender||constructed by Exim
+In the three cases that do not involve TCP/IP, the sender address is
+constructed from the login name of the user that called Exim and a default
+qualification domain (which can be set by the \qualify@_domain\ configuration
+option). For local or batch SMTP, a sender address that is passed using the
+SMTP \\MAIL\\ command is ignored. However, the system administrator may allow
+certain users (`trusted users') to specify a different sender address
+unconditionally, or all users to specify certain forms of different sender
+address. The \-f-\ option or the SMTP \\MAIL\\ command is used to specify these
+different addresses. See section ~~SECTtrustedadmin for details of trusted
+users, and the \untrusted@_set@_sender\ option for a way of allowing untrusted
+users to change sender addresses.
+
+Messages received by either of the non-interactive mechanisms are subject to
+checking by the non-SMTP ACL, if one is defined. Messages received using SMTP
+(either over TCP/IP, or interacting with a local process) can be checked by a
+number of ACLs that operate at different times during the SMTP session. Either
+individual recipients, or the entire message, can be rejected if local policy
+requirements are not met. The \*local@_scan()*\ function (see chapter
+~~CHAPlocalscan) is run for all incoming messages.
+
+Exim can be configured not to start a delivery process when a message is
+received; this can be unconditional, or depend on the number of incoming SMTP
+connections or the system load. In these situations, new messages wait on the
+queue until a queue runner process picks them up. However, in standard
+configurations under normal conditions, delivery is started as soon as a
+message is received.
+
+
+
+
+.section Handling an incoming message
+.index spool directory||files that hold a message
+.index file||how a message is held
+When Exim accepts a message, it writes two files in its spool directory. The
+first contains the envelope information, the current status of the message,
+and the header lines, and the second contains the body of the message. The
+names of the two spool files consist of the message id, followed by $tt{-H} for
+the file containing the envelope and header, and $tt{-D} for the data file.
+
+.index spool directory||\(input)\ sub-directory
+By default all these message files are held in a single directory called
+\(input)\ inside the general Exim spool directory. Some operating systems do
+not perform very well if the number of files in a directory gets very large; to
+improve performance in such cases, the \split@_spool@_directory\ option can be
+used. This causes Exim to split up the input files into 62 sub-directories
+whose names are single letters or digits.
+
+The envelope information consists of the address of the message's sender and
+the addresses of the recipients. This information is entirely separate from
+any addresses contained in the header lines. The status of the message includes
+a list of recipients who have already received the message. The format of the
+first spool file is described in chapter ~~CHAPspool.
+
+.index rewriting||addresses
+Address rewriting that is specified in the rewrite section of the configuration
+(see chapter ~~CHAPrewrite) is done once and for all on incoming addresses,
+both in the header lines and the envelope, at the time the message is accepted.
+If during the course of delivery additional addresses are generated (for
+example, via aliasing), these new addresses are rewritten as soon as they are
+generated. At the time a message is actually delivered (transported) further
+rewriting can take place; because this is a transport option, it can be
+different for different forms of delivery. It is also possible to specify the
+addition or removal of certain header lines at the time the message is
+delivered (see chapters ~~CHAProutergeneric and ~~CHAPtransportgeneric).
+
+
+.section Life of a message
+.index message||life of
+.index message||frozen
+A message remains in the spool directory until it is completely delivered to
+its recipients or to an error address, or until it is deleted by an
+administrator or by the user who originally created it. In cases when delivery
+cannot proceed -- for example, when a message can neither be delivered to its
+recipients nor returned to its sender, the message is marked `frozen' on the
+spool, and no more deliveries are attempted.
+
+.index frozen messages||thawing
+.index message||thawing frozen
+An administrator can `thaw' such messages when the problem has been corrected,
+and can also freeze individual messages by hand if necessary. In addition, an
+administrator can force a delivery error, causing a bounce message to be sent.
+
+.index \auto@_thaw\
+There is an option called \auto@_thaw\, which can be used to cause Exim to
+retry frozen messages after a certain time. When this is set, no message will
+remain on the queue for ever, because the delivery timeout will eventually be
+reached. Delivery failure reports (bounce messages) that reach this timeout are
+discarded.
+.index \timeout@_frozen@_after\
+There is also an option called \timeout@_frozen@_after\, which discards frozen
+messages after a certain time.
+
+.index message||log file for
+.index log||file for each message
+While Exim is working on a message, it writes information about each delivery
+attempt to the main log file. This includes successful, unsuccessful, and
+delayed deliveries for each recipient (see chapter ~~CHAPlog). The log lines
+are also written to a separate $it{message log} file for each message. These
+logs are solely for the benefit of the administrator, and are normally deleted
+along with the spool files when processing of a message is complete.
+The use of individual message logs can be disabled by setting
+\no@_message@_logs\; this might give an improvement in performance on very
+busy systems.
+
+.index journal file
+.index file||journal
+All the information Exim itself needs to set up a delivery is kept in the first
+spool file, along with the header lines. When a successful delivery occurs, the
+address is immediately written at the end of a journal file, whose name is the
+message id followed by $tt{-J}. At the end of a delivery run, if there are some
+addresses left to be tried again later, the first spool file (the $tt{-H} file)
+is updated to indicate which these are, and the journal file is then deleted.
+Updating the spool file is done by writing a new file and renaming it, to
+minimize the possibility of data loss.
+
+Should the system or the program crash after a successful delivery but before
+the spool file has been updated, the journal is left lying around. The next
+time Exim attempts to deliver the message, it reads the journal file and
+updates the spool file before proceeding. This minimizes the chances of double
+deliveries caused by crashes.
+
+
+.section Processing an address for delivery
+.rset SECTprocaddress "~~chapter.~~section"
+.index drivers||definition of
+.index router||definition of
+.index transport||definition of
+The main delivery processing elements of Exim are called $it{routers} and
+$it{transports}, and collectively these are known as $it{drivers}. Code for a
+number of them is provided in the source distribution, and compile-time options
+specify which ones are included in the binary. Run time options specify which
+ones are actually used for delivering messages.
+
+.index drivers||instance definition
+Each driver that is specified in the run time configuration is an \*instance*\
+of that particular driver type. Multiple instances are allowed; for example,
+you can set up several different \%smtp%\ transports, each with different
+option values that might specify different ports or different timeouts. Each
+instance has its own identifying name. In what follows we will normally use the
+instance name when discussing one particular instance (that is, one specific
+configuration of the driver), and the generic driver name when discussing
+the driver's features in general.
+
+A $it{router} is a driver that operates on an address, either determining how
+its delivery should happen, by routing it to a specific transport, or
+converting the address into one or more new addresses (for example, via an
+alias file). A router may also explicitly choose to fail an address, causing it
+to be bounced.
+
+A $it{transport} is a driver that transmits a copy of the message from Exim's
+spool to some destination. There are two kinds of transport: for a $it{local}
+transport, the destination is a file or a pipe on the local host, whereas for a
+$it{remote} transport the destination is some other host. A message is passed
+to a specific transport as a result of successful routing. If a message has
+several recipients, it may be passed to a number of different transports.
+
+.index preconditions||definition of
+An address is processed by passing it to each configured router instance in
+turn, subject to certain preconditions, until a router accepts the address or
+specifies that it should be bounced. We will describe this process in more
+detail shortly. As a simple example, the diagram below illustrates how each
+recipient address in a message is processed in a small configuration of three
+routers that are configured in various ways.
+
+.if ~~sys.fancy
+.figure "Routing an address" rm
+.indent 0
+.call aspic
+centre ~~sys.linelength;
+magnify 0.8;
+boundingbox 30;
+ ibox depth 14 "address";
+B: arrow down 44;
+ textdepth 14;
+A: box width 100 "first router" "conditions ok?";
+ arrow right "yes";
+C: box width 100 "run" "first router";
+ arrow down "fail";
+D: ibox depth 20 "address bounces";
+
+ arc clockwise from right of C "accept";
+ arrow down 10;
+ ibox "queue for" "transport";
+
+ arrow down from A align bottom of D plus (0,-20) "no"(-6,20)/r;
+E: box width 100 "second router" "conditions ok?";
+ arrow right "yes";
+F: box width 100 "run" "second router";
+ line right 100 "redirect";
+ line up align middle of B;
+ arrow left to middle of B "new addresses";
+
+ line down 20 from bottom left of F plus (30,0);
+ arrow left align centre of E "decline";
+
+ line down 20 from bottom right of F plus (-30,0);
+ arrow right "fail";
+ ibox width 64 "address" "bounces";
+
+ arrow down 64 from E "no"(-6,20)/r;
+G: box width 100 "third router" "conditions ok?";
+ arrow right "yes";
+H: box width 100 "run" "third router";
+ arc clockwise from right of H "accept";
+ arrow down 10;
+ ibox "queue for" "transport";
+
+ line down 20 from bottom of H;
+ arrow left align centre of G "decline";
+ arrow down 64 from G "no"(-6,20)/r;
+
+ ibox "no more routers" "address bounces";
+.endcall
+.endfigure
+.elif !~~html
+.display asis
+
+ address
+ |
+ |<------------- new addresses -----------------------------
+ V |
+ ----------------- ----------------- |
+ | first router |----- yes ----->| run |--- accept |
+ | conditions ok?| | first router | | |
+ ----------------- ----------------- | |
+ | | V |
+ no | fail | queue for |
+ | V transport |
+ | address bounces |
+ | |
+ V |
+ ----------------- ----------------- |
+ | second router |----- yes ----->| run |----redirect ----
+ | conditions ok?| | second router |
+ ----------------- -----------------
+ | | |
+ no | | |
+ |<-------- decline ----------- --- fail ---> address
+ | bounces
+ V
+ ----------------- -----------------
+ | third router |----- yes ----->| run |--- accept
+ | conditions ok?| | third router | |
+ ----------------- ----------------- |
+ | | V
+ no | | queue for
+ |<-------- decline --------------- transport
+ |
+ V
+ no more routers
+ address bounces
+.endd
+.else
+[(img src="routing.gif" alt="Routing an address")][(br)]
+.fi
+To make this a more concrete example, we'll describe it in terms of some actual
+routers, but remember, this is only an example. You can configure Exim's
+routers in many different ways, and there may be any number of routers in a
+configuration.
+
+The first router that is specified in a configuration is often one that handles
+addresses in domains that are not recognized specially by the local host. These
+are typically addresses for arbitrary domains on the Internet. A precondition
+is set up which looks for the special domains known to the host (for example,
+its own domain name), and the router is run for addresses that do $it{not}
+match. Typically, this is a router that looks up domains in the DNS in order to
+find the hosts to which this address routes. If it succeeds, the address is
+queued for a suitable SMTP transport; if it does not succeed, the router is
+configured to fail the address.
+
+The example pictured could be a configuration of this type. The second and
+third routers can only be run for addresses for which the preconditions for
+the first router are not met. If one of these preconditions checks the
+domain, the second and third routers are run only for domains that are somehow
+special to the local host.
+
+The second router does redirection -- also known as aliasing and forwarding.
+When it generates one or more new addresses from the original, each of them is
+routed independently from the start. Otherwise, the router may cause an address
+to fail, or it may simply decline to handle the address, in which case the
+address is passed to the next router.
+
+The final router in many configurations is one that checks to see if the
+address belongs to a local mailbox. The precondition may involve a check to
+see if the local part is the name of a login account, or it may look up the
+local part in a file or a database. If its preconditions are not met, or if
+the router declines, we have reached the end of the routers. When this happens,
+the address is bounced.
+
+
+.section Processing an address for verification
+.index router||for verification
+.index verifying||address, overview
+As well as being used to decide how to deliver to an address, Exim's routers
+are also used for \*address verification*\. Verification can be requested as
+one of the checks to be performed in an ACL for incoming messages, on both
+sender and recipient addresses, and it can be tested using the \-bv-\ and
+\-bvs-\ command line options.
+
+When an address is being verified, the routers are run in `verify mode'. This
+does not affect the way the routers work, but it is a state that can be
+detected. By this means, a router can be skipped or made to behave differently
+when verifying. A common example is a configuration in which the first router
+sends all messages to a message-scanning program, unless they have been
+previously scanned. Thus, the first router accepts all addresses without any
+checking, making it useless for verifying. Normally, the \no@_verify\ option
+would be set for such a router, causing it to be skipped in verify mode.
+
+
+
+.section Running an individual router
+.rset SECTrunindrou "~~chapter.~~section"
+.index router||running details
+.index preconditions||checking
+.index router||result of running
+As explained in the example above, a number of preconditions are checked before
+running a router. If any are not met, the router is skipped, and the address is
+passed to the next router. When all the preconditions on a router $it{are} met,
+the router is run. What happens next depends on the outcome, which is one of
+the following:
+.numberpars $.
+\*accept*\: The router accepts the address, and either queues it for a
+transport, or generates one or more `child' addresses. Processing the original
+address ceases,
+.index \unseen\ option
+unless the \unseen\ option is set on the router. This option
+can be used to set up multiple deliveries with different routing (for example,
+for keeping archive copies of messages). When \unseen\ is set, the address is
+passed to the next router. Normally, however, an \*accept*\ return marks the
+end of routing.
+
+.index case of local parts
+.index address||duplicate, discarding
+If child addresses are generated, Exim checks to see whether they are
+duplicates of any existing recipient addresses. During this check, local parts
+are treated as case-sensitive. Duplicate addresses are discarded. Each of the
+remaining child addresses is then processed independently, starting with the
+first router by default. It is possible to change this by setting the
+\redirect@_router\ option to specify which router to start at for child
+addresses. Unlike \pass@_router\ (see below) the router specified by
+\redirect@_router\ may be anywhere in the router configuration.
+.nextp
+\*pass*\: The router recognizes the address, but cannot handle it itself. It
+requests that the address be passed to another router. By default the address
+is passed to the next router, but this can be changed by setting the
+\pass@_router\ option. However, (unlike \redirect@_router\) the named router
+must be below the current router (to avoid loops).
+.nextp
+\*decline*\: The router declines to accept the address because it does not
+recognize it at all. By default, the address is passed to the next router, but
+this can be prevented by setting the \no@_more\ option. When \no@_more\ is set,
+all the remaining routers are skipped.
+.nextp
+\*fail*\: The router determines that the address should fail, and queues it for
+the generation of a bounce message. There is no further processing of the
+original address unless \unseen\ is set on the router.
+.nextp
+\*defer*\: The router cannot handle the address at the present time. (A database
+may be offline, or a DNS lookup may have timed out.) No further processing of
+the address happens in this delivery attempt. It is tried again next time the
+message is considered for delivery.
+.nextp
+\*error*\: There is some error in the router (for example, a syntax error in
+its configuration). The action is as for defer.
+.endp
+If an address reaches the end of the routers without having been accepted by
+any of them, it is bounced as unrouteable.
+The default error message in this situation is `unrouteable address', but you
+can set your own message by making use of the \cannot@_route@_message\ option.
+This can be set for any router; the value from the last router that `saw'
+the address is used.
+
+Sometimes while routing you want to fail a delivery when some conditions are
+met but others are not, instead of passing the address on for further routing.
+You can do this by having a second router that explicitly fails the delivery
+when the relevant conditions are met. The \%redirect%\ router has a `fail'
+facility for this purpose.
+
+
+
+.section Router preconditions
+.rset SECTrouprecon "~~chapter.~~section"
+.index router||preconditions, order of processing
+.index preconditions||order of processing
+The preconditions that are tested for each router are listed below, in the
+order in which they are tested. The individual configuration options are
+described in more detail in chapter ~~CHAProutergeneric.
+.numberpars $.
+The \local@_part@_prefix\ and \local@_part@_suffix\ options can specify that
+the local parts handled by the router may or must have certain prefixes and/or
+suffixes. If a mandatory affix (prefix or suffix) is not present, the router is
+skipped. These conditions are tested first. When an affix is present, it is
+removed from the local part before further processing, including the evaluation
+of any other conditions.
+.nextp
+Routers can be designated for use only when not verifying an address, that is,
+only when routing it for delivery (or testing its delivery routing). If the
+\verify\ option is set false, the router is skipped when Exim is verifying an
+address.
+Setting the \verify\ option actually sets two options, \verify@_sender\ and
+\verify@_recipient\, which independently control the use of the router for
+sender and recipient verification. You can set these options directly if
+you want a router to be used for only one type of verification.
+.nextp
+If the \address@_test\ option is set false, the router is skipped when Exim is
+run with the \-bt-\ option to test an address routing. This can be helpful when
+the first router sends all new messages to a scanner of some sort; it makes it
+possible to use \-bt-\ to test subsequent delivery routing without having to
+simulate the effect of the scanner.
+.nextp
+Routers can be designated for use only when verifying an address, as
+opposed to routing it for delivery. The \verify@_only\ option controls this.
+.nextp
+Certain routers can be explicitly skipped when running the routers to check an
+address given in the SMTP \\EXPN\\ command (see the \expn\ option).
+.nextp
+If the \domains\ option is set, the domain of the address must be in the set of
+domains that it defines.
+.nextp
+If the \local@_parts\ option is set, the local part of the address must be in
+the set of local parts that it defines. If \local@_part@_prefix\ or
+\local@_part@_suffix\ is in use, the prefix or suffix is removed from the local
+part before this check. If you want to do precondition tests on local parts
+that include affixes, you can do so by using a \condition\ option (see below)
+that uses the variables \$local@_part$\, \$local@_part@_prefix$\, and
+\$local@_part@_suffix$\ as necessary.
+.nextp
+If the \check@_local@_user\ option is set, the local part must be the name of
+an account on the local host.
+If this check succeeds, the uid and gid of the local user are placed in
+\$local@_user@_uid$\ and \$local@_user@_gid$\; these values can be used in the
+remaining preconditions.
+.nextp
+If the \router@_home@_directory\ option is set, it is expanded at this point,
+because it overrides the value of \$home$\. If this expansion were left till
+later, the value of \$home$\ as set by \check@_local@_user\ would be used in
+subsequent tests. Having two different values of \$home$\ in the same router
+could lead to confusion.
+.nextp
+If the \senders\ option is set, the envelope sender address must be in the set
+of addresses that it defines.
+.nextp
+If the \require@_files\ option is set, the existence or non-existence of
+specified files is tested.
+.nextp
+.index customizing||precondition
+If the \condition\ option is set, it is evaluated and tested. This option uses
+an expanded string to allow you to set up your own custom preconditions.
+Expanded strings are described in chapter ~~CHAPexpand.
+.endp
+
+Note that \require@_files\ comes near the end of the list, so you cannot use it
+to check for the existence of a file in which to lookup up a domain, local
+part, or sender. However, as these options are all expanded, you can use the
+\exists\ expansion condition to make such tests within each condition. The
+\require@_files\ option is intended for checking files that the router may be
+going to use internally, or which are needed by a specific transport (for
+example, \(.procmailrc)\).
+
+
+.section Delivery in detail
+.index delivery||in detail
+When a message is to be delivered, the sequence of events is as follows:
+.numberpars $.
+If a system-wide filter file is specified, the message is passed to it. The
+filter may add recipients to the message, replace the recipients, discard the
+message, cause a new message to be generated, or cause the message delivery to
+fail. The format of the system filter file is the same as for Exim user filter
+files, described in the separate document entitled
+.if ~~html
+[(A HREF="filter.html")]
+.fi
+\*Exim's interfaces to mail filtering*\.
+.if ~~html
+[(/A)]
+.fi
+.index Sieve filter||not available for system filter
+(\**Note**\: Sieve cannot be used for system filter files.)
+Some additional features are available in system filters -- see chapter
+~~CHAPsystemfilter for details. Note that a message is passed to the system
+filter only once per delivery attempt, however many recipients it has. However,
+if there are several delivery attempts because one or more addresses could not
+be immediately delivered, the system filter is run each time. The filter
+condition \first@_delivery\ can be used to detect the first run of the system
+filter.
+.nextp
+Each recipient address is offered to each configured router in turn, subject to
+its preconditions, until one is able to handle it. If no router can handle
+the address, that is, if they all decline, the address is failed. Because
+routers can be targeted at particular domains, several locally handled domains
+can be processed entirely independently of each other.
+.nextp
+.index routing||loops in
+.index loop||while routing
+A router that accepts an address may set up a local or a remote transport for
+it. However, the transport is not run at this time. Instead, the address is
+placed on a list for the particular transport, to be run later. Alternatively,
+the router may generate one or more new addresses (typically from alias,
+forward, or filter files). New addresses are fed back into this process from
+the top, but in order to avoid loops, a router ignores any address which has an
+identically-named ancestor that was processed by itself.
+.nextp
+When all the routing has been done, addresses that have been successfully
+handled are passed to their assigned transports. When local transports are
+doing real local deliveries, they handle only one address at a time, but if a
+local transport is being used as a pseudo-remote transport (for example, to
+collect batched SMTP messages for transmission by some other means) multiple
+addresses can be handled. Remote transports can always handle more than one
+address at a time, but can be configured not to do so, or to restrict multiple
+addresses to the same domain.
+.nextp
+Each local delivery to a file or a pipe runs in a separate process under a
+non-privileged uid, and these deliveries are run one at a time. Remote
+deliveries also run in separate processes, normally under a uid that is private
+to Exim (`the Exim user'), but in this case, several remote deliveries can be
+run in parallel. The maximum number of simultaneous remote deliveries for any
+one message is set by the \remote@_max@_parallel\ option.
+.em
+The order in which deliveries are done is not defined, except that all local
+deliveries happen before any remote deliveries.
+.nem
+.nextp
+.index queue runner
+When it encounters a local delivery during a queue run, Exim checks its retry
+database to see if there has been a previous temporary delivery failure for the
+address before running the local transport. If there was a previous failure,
+Exim does not attempt a new delivery until the retry time for the address is
+reached. However, this happens only for delivery attempts that are part of a
+queue run. Local deliveries are always attempted when delivery immediately
+follows message reception, even if retry times are set for them. This makes for
+better behaviour if one particular message is causing problems (for example,
+causing quota overflow, or provoking an error in a filter file).
+.nextp
+.index delivery||retry in remote transports
+Remote transports do their own retry handling, since an address may be
+deliverable to one of a number of hosts, each of which may have a different
+retry time. If there have been previous temporary failures and no host has
+reached its retry time, no delivery is attempted, whether in a queue run or
+not. See chapter ~~CHAPretry for details of retry strategies.
+.nextp
+If there were any permanent errors, a bounce message is returned to an
+appropriate address (the sender in the common case), with details of the error
+for each failing address. Exim can be configured to send copies of bounce
+messages to other addresses.
+.nextp
+.index delivery||deferral
+If one or more addresses suffered a temporary failure, the message is left on
+the queue, to be tried again later. Delivery of these addresses is said to be
+\*deferred*\.
+.nextp
+When all the recipient addresses have either been delivered or bounced,
+handling of the message is complete. The spool files and message log are
+deleted, though the message log can optionally be preserved if required.
+.endp
+
+
+.section Retry mechanism
+.index delivery||retry mechanism
+.index retry||description of mechanism
+.index queue runner
+Exim's mechanism for retrying messages that fail to get delivered at the first
+attempt is the queue runner process. You must either run an Exim daemon that
+uses the \-q-\ option with a time interval to start queue runners at regular
+intervals, or use some other means (such as \*cron*\) to start them. If you do
+not arrange for queue runners to be run, messages that fail temporarily at the
+first attempt will remain on your queue for ever. A queue runner process works
+it way through the queue, one message at a time, trying each delivery that has
+passed its retry time.
+You can run several queue runners at once.
+
+Exim uses a set of configured rules to determine when next to retry the failing
+address (see chapter ~~CHAPretry). These rules also specify when Exim should
+give up trying to deliver to the address, at which point it generates a bounce
+message. If no retry rules are set for a particular host, address, and error
+combination, no retries are attempted, and temporary errors are treated as
+permanent.
+
+
+.section Temporary delivery failure
+.index delivery||temporary failure
+There are many reasons why a message may not be immediately deliverable to a
+particular address. Failure to connect to a remote machine (because it, or the
+connection to it, is down) is one of the most common. Temporary failures may be
+detected during routing as well as during the transport stage of delivery.
+Local deliveries may be delayed if NFS files are unavailable, or if a mailbox
+is on a file system where the user is over quota. Exim can be configured to
+impose its own quotas on local mailboxes; where system quotas are set they will
+also apply.
+
+If a host is unreachable for a period of time, a number of messages may be
+waiting for it by the time it recovers, and sending them in a single SMTP
+connection is clearly beneficial. Whenever a delivery to a remote host is
+deferred,
+.index hints database
+Exim makes a note in its hints database, and whenever a successful
+SMTP delivery has happened, it looks to see if any other messages are waiting
+for the same host. If any are found, they are sent over the same SMTP
+connection, subject to a configuration limit as to the maximum number in any
+one connection.
+
+
+
+.section Permanent delivery failure
+.index delivery||permanent failure
+.index bounce message||when generated
+When a message cannot be delivered to some or all of its intended recipients, a
+bounce message is generated. Temporary delivery failures turn into permanent
+errors when their timeout expires. All the addresses that fail in a given
+delivery attempt are listed in a single message. If the original message has
+many recipients, it is possible for some addresses to fail in one delivery
+attempt and others to fail subsequently, giving rise to more than one bounce
+message. The wording of bounce messages can be customized by the administrator.
+See chapter ~~CHAPemsgcust for details.
+
+.index ::X-Failed-Recipients:: header line
+Bounce messages contain an ::X-Failed-Recipients:: header line that lists the
+failed addresses, for the benefit of programs that try to analyse such messages
+automatically.
+
+.index bounce message||recipient of
+A bounce message is normally sent to the sender of the original message, as
+obtained from the message's envelope. For incoming SMTP messages, this is the
+address given in the \\MAIL\\ command. However, when an address is
+expanded via a forward or alias file, an alternative address can be specified
+for delivery failures of the generated addresses. For a mailing list expansion
+(see section ~~SECTmailinglists) it is common to direct bounce messages to the
+manager of the list.
+
+
+
+.section Failures to deliver bounce messages
+.index bounce message||failure to deliver
+If a bounce message (either locally generated or received from a remote host)
+itself suffers a permanent delivery failure, the message is left on the queue,
+but it is frozen, awaiting the attention of an administrator. There are options
+which can be used to make Exim discard such failed messages, or to keep them
+for only a short time (see \timeout@_frozen@_after\ and
+\ignore@_bounce@_errors@_after\).
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Building and installing Exim
+.set runningfoot "building/installing"
+
+.index building Exim
+.section Unpacking
+Exim is distributed as a gzipped or bzipped tar file which, when upacked,
+creates a directory with the name of the current release (for example,
+\(exim-~~version)\) into which the following files are placed:
+.display rm
+.if !~~sys.fancy && ~~sgcal
+.tabs 16
+.else
+.tabs 22
+.fi
+\(ACKNOWLEDGMENTS)\ $t contains some acknowledgments
+.newline
+\(CHANGES)\ $t contains a reference to where changes are documented
+\(LICENCE)\ $t the GNU General Public Licence
+\(Makefile)\ $t top-level make file
+\(NOTICE)\ $t conditions for the use of Exim
+\(README)\ $t list of files, directories and simple build instructions
+.endd
+Other files whose names begin with \(README)\ may also be present. The
+following subdirectories are created:
+.display rm
+.if !~~sys.fancy && ~~sgcal
+.tabs 16
+.else
+.tabs 22
+.fi
+\(Local)\ $t an empty directory for local configuration files
+\(OS)\ $t OS-specific files
+\(doc)\ $t documentation files
+\(exim@_monitor)\$t source files for the Exim monitor
+\(scripts)\ $t scripts used in the build process
+\(src)\ $t remaining source files
+\(util)\ $t independent utilities
+.endd
+The main utility programs are contained in the \(src)\ directory, and are built
+with the Exim binary. The \(util)\ directory contains a few optional scripts
+that may be useful to some sites.
+
+.section Multiple machine architectures and operating systems
+.index building Exim||multiple OS/architectures
+The building process for Exim is arranged to make it easy to build binaries for
+a number of different architectures and operating systems from the same set of
+source files. Compilation does not take place in the \(src)\ directory. Instead,
+a \*build directory*\ is created for each architecture and operating system.
+.index symbolic link||to build directory
+Symbolic links to the sources are installed in this directory, which is where
+the actual building takes place.
+
+In most cases, Exim can discover the machine architecture and operating system
+for itself, but the defaults can be overridden if necessary.
+
+.section DBM libraries
+.rset SECTdb "~~chapter.~~section"
+.index DBM||libraries, discussion of
+.index hints database||DBM files used for
+Even if you do not use any DBM files in your configuration, Exim still needs a
+DBM library in order to operate, because it uses indexed files for its hints
+databases. Unfortunately, there are a number of DBM libraries in existence, and
+different operating systems often have different ones installed.
+
+.index Solaris||DBM library for
+.index IRIX, DBM library for
+.index BSD, DBM library for
+.index Linux, DBM library for
+If you are using Solaris, IRIX, one of the modern BSD systems, or a modern
+Linux distribution, the DBM configuration should happen automatically, and you
+may be able to ignore this section. Otherwise, you may have to learn more than
+you would like about DBM libraries from what follows.
+
+.index \*ndbm*\ DBM library
+Licensed versions of Unix normally contain a library of DBM functions operating
+via the \*ndbm*\ interface, and this is what Exim expects by default. Free
+versions of Unix seem to vary in what they contain as standard. In particular,
+some early versions of Linux have no default DBM library, and different
+distributors have chosen to bundle different libraries with their packaged
+versions. However, the more recent releases seem to have standardised on the
+Berkeley DB library.
+
+Different DBM libraries have different conventions for naming the files they
+use. When a program opens a file called \(dbmfile)\, there are four
+possibilities:
+.numberpars
+A traditional \*ndbm*\ implementation, such as that supplied as part of
+Solaris, operates on two files called \(dbmfile.dir)\ and \(dbmfile.pag)\.
+.nextp
+.index \*gdbm*\ DBM library
+The GNU library, \*gdbm*\, operates on a single file. If used via its \*ndbm*\
+compatibility interface it makes two different hard links to it with names
+\(dbmfile.dir)\ and \(dbmfile.pag)\, but if used via its native interface, the
+file name is used unmodified.
+.nextp
+.index Berkeley DB library
+The Berkeley DB package, if called via its \*ndbm*\ compatibility interface,
+operates on a single file called \(dbmfile.db)\, but otherwise looks to the
+programmer exactly the same as the traditional \*ndbm*\ implementation.
+.nextp
+If the Berkeley package is used in its native mode, it operates on a single
+file called \(dbmfile)\; the programmer's interface is somewhat different to
+the traditional \*ndbm*\ interface.
+.nextp
+To complicate things further, there are several very different versions of the
+Berkeley DB package. Version 1.85 was stable for a very long time, releases
+2.$it{x} and 3.$it{x} were current for a while, but the latest versions are now
+numbered 4.$it{x}. Maintenance of some of the earlier releases has ceased. All
+versions of Berkeley DB can be obtained from
+.display rm
+\?http://www.sleepycat.com/?\
+.endd
+.nextp
+.index \*tdb*\ DBM library
+Yet another DBM library, called \*tdb*\, has become available from
+.display rm
+\?http://download.sourceforge.net/tdb?\
+.endd
+It has its own interface, and also operates on a single file.
+.endp
+.index \\USE@_DB\\
+.index DBM||libraries, configuration for building
+Exim and its utilities can be compiled to use any of these interfaces. In order
+to use any version of the Berkeley DB package in native mode, you must set
+\\USE@_DB\\ in an appropriate configuration file (typically
+\(Local/Makefile)\). For example:
+.display asis
+USE_DB=yes
+.endd
+Similarly, for gdbm you set \\USE@_GDBM\\, and for tdb you set \\USE@_TDB\\. An
+error is diagnosed if you set more than one of these.
+
+At the lowest level, the build-time configuration sets none of these options,
+thereby assuming an interface of type (1). However, some operating system
+configuration files (for example, those for the BSD operating systems and
+Linux) assume type (4) by setting \\USE@_DB\\ as their default, and the
+configuration files for Cygwin set \\USE@_GDBM\\. Anything you set in
+\(Local/Makefile)\, however, overrides these system defaults.
+
+As well as setting \\USE@_DB\\, \\USE@_GDBM\\, or \\USE@_TDB\\, it may also be
+necessary to set \\DBMLIB\\, to cause inclusion of the appropriate library, as
+in one of these lines:
+.display asis
+DBMLIB = -ldb
+DBMLIB = -ltdb
+.endd
+Settings like that will work if the DBM library is installed in the standard
+place. Sometimes it is not, and the library's header file may also not be in
+the default path. You may need to set \\INCLUDE\\ to specify where the header
+file is, and to specify the path to the library more fully in \\DBMLIB\\, as in
+this example:
+.display asis
+INCLUDE=-I/usr/local/include/db-4.1
+DBMLIB=/usr/local/lib/db-4.1/libdb.a
+.endd
+
+There is further detailed discussion about the various DBM libraries in the
+file \(doc/dbm.discuss.txt)\ in the Exim distribution.
+
+
+.section Pre-building configuration
+.index building Exim||pre-building configuration
+.index configuration for building Exim
+.index \(Local/Makefile)\
+.index \(src/EDITME)\
+Before building Exim, a local configuration file that specifies options
+independent of any operating system has to be created with the name
+\(Local/Makefile)\. A template for this file is supplied as the file
+\(src/EDITME)\, and it contains full descriptions of all the option settings
+therein. These descriptions are therefore not repeated here. If you are
+building Exim for the first time, the simplest thing to do is to copy
+\(src/EDITME)\ to \(Local/Makefile)\, then read it and edit it appropriately.
+
+There are three settings that you must supply, because Exim will not build
+without them. They are the location of the run time configuration file
+(\\CONFIGURE@_FILE\\), the directory in which Exim binaries will be installed
+(\\BIN@_DIRECTORY\\), and the identity of the Exim user (\\EXIM@_USER\\ and
+maybe \\EXIM@_GROUP\\ as well). The value of \\CONFIGURE@_FILE\\ can in fact be
+a colon-separated list of file names; Exim uses the first of them that exists.
+
+There are a few other parameters that can be specified either at build time or
+at run time, to enable the same binary to be used on a number of different
+machines. However, if the locations of Exim's spool directory and log file
+directory (if not within the spool directory) are fixed, it is recommended that
+you specify them in \(Local/Makefile)\ instead of at run time, so that errors
+detected early in Exim's execution (such as a malformed configuration file) can
+be logged.
+
+.index \(Local/eximon.conf)\
+.index \(exim@_monitor/EDITME)\
+If you are going to build the Exim monitor, a similar configuration process is
+required. The file \(exim@_monitor/EDITME)\ must be edited appropriately for
+your installation and saved under the name \(Local/eximon.conf)\. If you are
+happy with the default settings described in \(exim@_monitor/EDITME)\,
+\(Local/eximon.conf)\ can be empty, but it must exist.
+
+This is all the configuration that is needed in straightforward cases for known
+operating systems. However, the building process is set up so that it is easy
+to override options that are set by default or by operating-system-specific
+configuration files, for example to change the name of the C compiler, which
+defaults to \gcc\. See section ~~SECToverride below for details of how to do
+this.
+
+
+.section Support for iconv()
+.index \*iconv()*\ support
+The contents of header lines in messages may be encoded according to the rules
+described RFC 2047. This makes it possible to transmit characters that are not
+in the ASCII character set, and to label them as being in a particular
+character set. When Exim is inspecting header lines by means of the \@$h@_\
+mechanism, it decodes them, and translates them into a specified character set
+(default ISO-8859-1). The translation is possible only if the operating system
+supports the \*iconv()*\ function.
+
+However, some of the operating systems that supply \*iconv()*\ do not support
+very many conversions. The GNU \libiconv\ library (available from
+\?http:/@/www.gnu.org/software/libiconv/?\) can be installed on such systems to
+remedy this deficiency, as well as on systems that do not supply \*iconv()*\ at
+all. After installing \libiconv\, you should add
+.display asis
+HAVE_ICONV=yes
+.endd
+to your \(Local/Makefile)\ and rebuild Exim.
+
+
+.section Including TLS/SSL encryption support
+.rset SECTinctlsssl "~~chapter.~~section"
+.index TLS||including support for TLS
+.index encryption||including support for
+.index \\SUPPORT@_TLS\\
+.index OpenSSL||building Exim with
+.index GnuTLS||building Exim with
+Exim can be built to support encrypted SMTP connections, using the \\STARTTLS\\
+command as per RFC 2487. It can also support legacy clients that expect to
+start a TLS session immediately on connection to a non-standard port (see the
+\-tls-on-connect-\ command line option).
+
+If you want to build Exim with TLS support, you must first install either the
+OpenSSL or GnuTLS library. There is no cryptographic code in Exim itself for
+implementing SSL.
+
+If OpenSSL is installed, you should set
+.display asis
+SUPPORT_TLS=yes
+TLS_LIBS=-lssl -lcrypto
+.endd
+in \(Local/Makefile)\. You may also need to specify the locations of the
+OpenSSL library and include files. For example:
+.display asis
+SUPPORT_TLS=yes
+TLS_LIBS=-L/usr/local/openssl/lib -lssl -lcrypto
+TLS_INCLUDE=-I/usr/local/openssl/include/
+.endd
+
+If GnuTLS is installed, you should set
+.index \\USE@_GNUTLS\\
+.display asis
+SUPPORT_TLS=yes
+USE_GNUTLS=yes
+TLS_LIBS=-lgnutls -ltasn1 -lgcrypt
+.endd
+in \(Local/Makefile)\, and again you may need to specify the locations of the
+library and include files. For example:
+.display asis
+SUPPORT_TLS=yes
+USE_GNUTLS=yes
+TLS_LIBS=-L/usr/gnu/lib -lgnutls -ltasn1 -lgcrypt
+TLS_INCLUDE=-I/usr/gnu/include
+.endd
+You do not need to set \\TLS@_INCLUDE\\ if the relevant directory is already
+specified in \\INCLUDE\\. Details of how to configure Exim to make use of TLS
+are given in chapter ~~CHAPTLS.
+
+
+
+.section Use of tcpwrappers
+.index tcpwrappers, building Exim to support
+.index \\USE@_TCP@_WRAPPERS\\
+Exim can be linked with the \*tcpwrappers*\ library in order to check incoming
+SMTP calls using the \*tcpwrappers*\ control files. This may be a convenient
+alternative to Exim's own checking facilities for installations that are
+already making use of \*tcpwrappers*\ for other purposes. To do this, you should
+set \\USE@_TCP@_WRAPPERS\\ in \(Local/Makefile)\, arrange for the file
+\(tcpd.h)\ to be available at compile time, and also ensure that the library
+\(libwrap.a)\ is available at link time, typically by including \-lwrap-\ in
+\\EXTRALIBS@_EXIM\\. For example, if \*tcpwrappers*\ is installed in
+\(/usr/local)\, you might have
+.display
+USE@_TCP@_WRAPPERS=yes
+CFLAGS=-O -I/usr/local/include
+.newline
+EXTRALIBS@_EXIM=-L/usr/local/lib -lwrap
+.endd
+in \(Local/Makefile)\. The name to use in the \*tcpwrappers*\ control files is
+`exim'. For example, the line
+.display
+exim : LOCAL 192.168.1. .friendly.domain.example
+.endd
+in your \(/etc/hosts.allow)\ file allows connections from the local host, from
+the subnet 192.168.1.0/24, and from all hosts in \*friendly.domain.example*\.
+All other connections are denied. Consult the \*tcpwrappers*\ documentation for
+further details.
+
+
+.section Including support for IPv6
+.index IPv6||including support for
+Exim contains code for use on systems that have IPv6 support. Setting
+\\HAVE@_IPV6=YES\\ in \(Local/Makefile)\ causes the IPv6 code to be included;
+it may also be necessary to set \\IPV6@_INCLUDE\\ and \\IPV6@_LIBS\\ on systems
+where the IPv6 support is not fully integrated into the normal include and
+library files.
+
+IPv6 is still changing rapidly. Two different types of DNS record for handling
+IPv6 addresses have been defined. AAAA records are already in use, and are
+currently seen as the `mainstream', but another record type called A6 is being
+argued about. Its status is currently `experimental'. Exim has support for A6
+records, but this is included only if you set \\SUPPORT@_A6=YES\\ in
+\(Local/Makefile)\.
+
+
+.section The building process
+.index build directory
+Once \(Local/Makefile)\ (and \(Local/eximon.conf)\, if required) have been
+created, run \*make*\ at the top level. It determines the architecture and
+operating system types, and creates a build directory if one does not exist.
+For example, on a Sun system running Solaris 8, the directory
+\(build-SunOS5-5.8-sparc)\ is created.
+.index symbolic link||to source files
+Symbolic links to relevant source files are installed in the build directory.
+
+.em
+\**Warning**\: The \-j-\ (parallel) flag must not be used with \*make*\; the
+building process fails if it is set.
+.nem
+
+If this is the first time \*make*\ has been run, it calls a script that builds
+a make file inside the build directory, using the configuration files from the
+\(Local)\ directory. The new make file is then passed to another instance of
+\*make*\. This does the real work, building a number of utility scripts, and
+then compiling and linking the binaries for the Exim monitor (if configured), a
+number of utility programs, and finally Exim itself. The command \*make
+makefile*\ can be used to force a rebuild of the make file in the build
+directory, should this ever be necessary.
+
+If you have problems building Exim, check for any comments there may be in the
+\(README)\ file concerning your operating system, and also take a look at the
+.if ~~html
+[(A HREF="FAQ.html")]
+.fi
+FAQ,
+.if ~~html
+[(/A)]
+.fi
+where some common problems are covered.
+
+
+
+.section Overriding build-time options for Exim
+.index build-time options, overriding
+.rset SECToverride "~~chapter.~~section"
+The main make file that is created at the beginning of the building process
+consists of the concatenation of a number of files which set configuration
+values, followed by a fixed set of \*make*\ instructions. If a value is set
+more than once, the last setting overrides any previous ones. This provides a
+convenient way of overriding defaults. The files that are concatenated are, in
+order:
+.display rm
+\(OS/Makefile-Default)\
+\(OS/Makefile-)\<<ostype>>
+\(Local/Makefile)\
+\(Local/Makefile-)\<<ostype>>
+\(Local/Makefile-)\<<archtype>>
+\(Local/Makefile-)\<<ostype>>-<<archtype>>
+\(OS/Makefile-Base)\
+.endd
+.index \(Local/Makefile)\
+where <<ostype>> is the operating system type and <<archtype>> is the
+.index building Exim||operating system type
+.index building Exim||architecture type
+architecture type. \(Local/Makefile)\ is required to exist, and the building
+process fails if it is absent. The other three \(Local)\ files are optional,
+and are often not needed.
+
+The values used for <<ostype>> and <<archtype>> are obtained from scripts
+called \(scripts/os-type)\ and \(scripts/arch-type)\ respectively. If either of
+the environment variables \\EXIM@_OSTYPE\\ or \\EXIM@_ARCHTYPE\\ is set, their
+values are used, thereby providing a means of forcing particular settings.
+Otherwise, the scripts try to get values from the \uname\ command. If this
+fails, the shell variables \\OSTYPE\\ and \\ARCHTYPE\\ are inspected. A number
+of $it{ad hoc} transformations are then applied, to produce the standard names
+that Exim expects. You can run these scripts directly from the shell in order
+to find out what values are being used on your system.
+
+
+\(OS/Makefile-Default)\ contains comments about the variables that are set
+therein. Some (but not all) are mentioned below. If there is something that
+needs changing, review the contents of this file and the contents of the make
+file for your operating system (\(OS/Makefile-<<ostype>>)\) to see what the
+default values are.
+
+
+.index building Exim||overriding default settings
+If you need to change any of the values that are set in \(OS/Makefile-Default)\
+or in \(OS/Makefile-<<ostype>>)\, or to add any new definitions, you do not
+need to change the original files. Instead, you should make the changes by
+putting the new values in an appropriate \(Local)\ file. For example,
+.index Tru64-Unix build-time settings
+when building Exim in many releases of the Tru64-Unix (formerly Digital UNIX,
+formerly DEC-OSF1) operating system, it is necessary to specify that the C
+compiler is called \*cc*\ rather than \*gcc*\. Also, the compiler must be
+called with the option \-std1-\, to make it recognize some of the features of
+Standard C that Exim uses. (Most other compilers recognize Standard C by
+default.) To do this, you should create a file called \(Local/Makefile-OSF1)\
+containing the lines
+.display
+CC=cc
+CFLAGS=-std1
+.endd
+If you are compiling for just one operating system, it may be easier to put
+these lines directly into \(Local/Makefile)\.
+
+Keeping all your local configuration settings separate from the distributed
+files makes it easy to transfer them to new versions of Exim simply by copying
+the contents of the \(Local)\ directory.
+
+
+.index NIS lookup type||including support for
+.index NIS@+ lookup type||including support for
+.index LDAP||including support for
+.index lookup||inclusion in binary
+Exim contains support for doing LDAP, NIS, NIS+, and other kinds of file
+lookup, but not all systems have these components installed, so the default is
+not to include the relevant code in the binary. All the different kinds of file
+and database lookup that Exim supports are implemented as separate code modules
+which are included only if the relevant compile-time options are set. In the
+case of LDAP, NIS, and NIS+, the settings for \(Local/Makefile)\ are:
+.display asis
+LOOKUP_LDAP=yes
+LOOKUP_NIS=yes
+LOOKUP_NISPLUS=yes
+.endd
+and similar settings apply to the other lookup types. They are all listed in
+\(src/EDITME)\. In most cases the relevant include files and interface
+libraries need to be installed before compiling Exim.
+.index cdb||including support for
+However, in the case of cdb, which is included in the binary only if
+.display asis
+LOOKUP_CDB=yes
+.endd
+is set, the code is entirely contained within Exim, and no external include
+files or libraries are required. When a lookup type is not included in the
+binary, attempts to configure Exim to use it cause run time configuration
+errors.
+
+.index Perl||including support for
+Exim can be linked with an embedded Perl interpreter, allowing Perl
+subroutines to be called during string expansion. To enable this facility,
+.display asis
+EXIM_PERL=perl.o
+.endd
+must be defined in \(Local/Makefile)\. Details of this facility are given in
+chapter ~~CHAPperl.
+
+.index X11 libraries, location of
+The location of the X11 libraries is something that varies a lot between
+operating systems, and of course there are different versions of X11 to cope
+with. Exim itself makes no use of X11, but if you are compiling the Exim
+monitor, the X11 libraries must be available.
+The following three variables are set in \(OS/Makefile-Default)\:
+.display asis
+X11=/usr/X11R6
+XINCLUDE=-I$(X11)/include
+XLFLAGS=-L$(X11)/lib
+.endd
+These are overridden in some of the operating-system configuration files. For
+example, in \(OS/Makefile-SunOS5)\ there is
+.display asis
+X11=/usr/openwin
+XINCLUDE=-I$(X11)/include
+XLFLAGS=-L$(X11)/lib -R$(X11)/lib
+.endd
+If you need to override the default setting for your operating system, place a
+definition of all three of these variables into your
+\(Local/Makefile-<<ostype>>)\ file.
+
+.index \\EXTRALIBS\\
+If you need to add any extra libraries to the link steps, these can be put in a
+variable called \\EXTRALIBS\\, which appears in all the link commands, but by
+default is not defined. In contrast, \\EXTRALIBS@_EXIM\\ is used only on the
+command for linking the main Exim binary, and not for any associated utilities.
+.index DBM||libraries, configuration for building
+There is also \\DBMLIB\\, which appears in the link commands for binaries that
+use DBM functions (see also section ~~SECTdb). Finally, there is
+\\EXTRALIBS@_EXIMON\\, which appears only in the link step for the Exim monitor
+binary, and which can be used, for example, to include additional X11
+libraries.
+
+.index configuration file||editing
+The make file copes with rebuilding Exim correctly if any of the configuration
+files are edited. However, if an optional configuration file is deleted, it is
+necessary to touch the associated non-optional file (that is, \(Local/Makefile)\
+or \(Local/eximon.conf)\) before rebuilding.
+
+.section OS-specific header files
+.index \(os.h)\
+.index building Exim||OS-specific C header files
+The \(OS)\ directory contains a number of files with names of the form
+\(os.h-<<ostype>>)\. These are system-specific C header files that should not
+normally need to be changed. There is a list of macro settings that are
+recognized in the file \(OS/os.configuring)\, which should be consulted if you
+are porting Exim to a new operating system.
+
+
+.section Overriding build-time options for the monitor
+.index building Eximon||overriding default options
+A similar process is used for overriding things when building the Exim monitor,
+where the files that are involved are
+.display rm
+\(OS/eximon.conf-Default)\
+\(OS/eximon.conf-)\<<ostype>>
+\(Local/eximon.conf)\
+\(Local/eximon.conf-)\<<ostype>>
+\(Local/eximon.conf-)\<<archtype>>
+\(Local/eximon.conf-)\<<ostype>>-<<archtype>>
+.endd
+.index \(Local/eximon.conf)\
+As with Exim itself, the final three files need not exist, and in this case the
+\(OS/eximon.conf-<<ostype>>)\ file is also optional. The default values in
+\(OS/eximon.conf-Default)\ can be overridden dynamically by setting environment
+variables of the same name, preceded by \\EXIMON@_\\. For example, setting
+\\EXIMON@_LOG@_DEPTH\\ in the environment overrides the value of
+\\LOG@_DEPTH\\ at run time.
+
+
+
+.section Installing Exim binaries and scripts
+.index installing Exim
+.index \\BIN@_DIRECTORY\\
+The command \*make install*\ runs the \*exim@_install*\ script with no
+arguments. The script copies binaries and utility scripts into the directory
+whose name is specified by the \\BIN@_DIRECTORY\\ setting in
+\(Local/Makefile)\.
+
+Exim's run time configuration file is named by the \\CONFIGURE@_FILE\\ setting
+.index \\CONFIGURE@_FILE\\
+in \(Local/Makefile)\. If this names a single file, and the file does not
+exist, the default configuration file \(src/configure.default)\ is copied there
+by the installation script. If a run time configuration file already exists, it
+is left alone. If \\CONFIGURE@_FILE\\ is a colon-separated list, naming several
+alternative files, no default is installed.
+
+.index system aliases file
+.index \(/etc/aliases)\
+One change is made to the default configuration file when it is installed: the
+default configuration contains a router that references a system aliases file.
+The path to this file is set to the value specified by
+\\SYSTEM@_ALIASES@_FILE\\ in \(Local/Makefile)\ (\(/etc/aliases)\ by default).
+If the system aliases file does not exist, the installation script creates it,
+and outputs a comment to the user.
+
+The created file contains no aliases, but it does contain comments about the
+aliases a site should normally have. Mail aliases have traditionally been
+kept in \(/etc/aliases)\. However, some operating systems are now using
+\(/etc/mail/aliases)\. You should check if yours is one of these, and change
+Exim's configuration if necessary.
+
+The default configuration uses the local host's name as the only local domain,
+and is set up to do local deliveries into the shared directory \(/var/mail)\,
+running as the local user. System aliases and \(.forward)\ files in users' home
+directories are supported, but no NIS or NIS+ support is configured. Domains
+other than the name of the local host are routed using the DNS, with delivery
+over SMTP.
+
+The install script copies files only if they are newer than the files they are
+going to replace. The Exim binary is required to be owned by root and have the
+\*setuid*\ bit set,
+.index setuid||installing Exim with
+for normal configurations. Therefore, you must run \*make install*\ as root so
+that it can set up the Exim binary in this way. However, in some special
+situations (for example, if a host is doing no local deliveries) it may be
+possible to run Exim without making the binary setuid root (see chapter
+~~CHAPsecurity for details).
+
+It is possible to install Exim for special purposes (such as building a binary
+distribution) in a private part of the file system. You can do this by a
+command such as
+.display asis
+make DESTDIR=/some/directory/ install
+.endd
+This has the effect of pre-pending the specified directory to all the file
+paths, except the name of the system aliases file that appears in the default
+configuration. (If a default alias file is created, its name \*is*\ modified.)
+For backwards compatibility, \\ROOT\\ is used if \\DESTDIR\\ is not set,
+but this usage is deprecated.
+
+.index installing Exim||what is not installed
+Running \*make install*\ does not copy the Exim 4 conversion script
+\*convert4r4*\, or the \*pcretest*\ test program. You will probably run the
+first of these only once (if you are upgrading from Exim 3), and the second
+isn't really part of Exim. None of the documentation files in the \(doc)\
+directory are copied, except for the info files when you have set
+\\INFO@_DIRECTORY\\, as described in section ~~SECTinsinfdoc below.
+
+For the utility programs, old versions are renamed by adding the suffix \(.O)\
+to their names. The Exim binary itself, however, is handled differently. It is
+installed under a name that includes the version number and the compile number,
+for example \(exim-~~version-1)\. The script then arranges for a symbolic link
+called \(exim)\ to point to the binary. If you are updating a previous version
+of Exim, the script takes care to ensure that the name \(exim)\ is never absent
+from the directory (as seen by other processes).
+
+.index installing Exim||testing the script
+If you want to see what the \*make install*\ will do before running it for
+real, you can pass the \-n-\ option to the installation script by this command:
+.display asis
+make INSTALL_ARG=-n install
+.endd
+The contents of the variable \\INSTALL@_ARG\\ are passed to the installation
+script. You do not need to be root to run this test. Alternatively, you can run
+the installation script directly, but this must be from within the build
+directory. For example, from the top-level Exim directory you could use this
+command:
+.display
+(cd build-SunOS5-5.5.1-sparc; ../scripts/exim@_install -n)
+.endd
+
+.index installing Exim||install script options
+There are two other options that can be supplied to the installation script.
+.numberpars $.
+\-no@_chown-\ bypasses the call to change the owner of the installed binary
+to root, and the call to make it a setuid binary.
+.nextp
+\-no@_symlink-\ bypasses the setting up of the symbolic link \(exim)\ to the
+installed binary.
+.endp
+\\INSTALL@_ARG\\ can be used to pass these options to the script. For example:
+.display asis
+make INSTALL_ARG=-no_symlink install
+.endd
+
+The installation script can also be given arguments specifying which files are
+to be copied. For example, to install just the Exim binary, and nothing else,
+without creating the symbolic link, you could use:
+.display asis
+make INSTALL_ARG='-no_symlink exim' install
+.endd
+
+
+.section Installing info documentation
+.rset SECTinsinfdoc "~~chapter.~~section"
+.index installing Exim||\*info*\ documentation
+Not all systems use the GNU \*info*\ system for documentation, and for this
+reason, the Texinfo source of Exim's documentation is not included in the main
+distribution. Instead it is available separately from the ftp site (see section
+~~SECTavail).
+
+If you have defined \\INFO@_DIRECTORY\\ in \(Local/Makefile)\ and the Texinfo
+source of the documentation is found in the source tree, running \*make
+install*\ automatically builds the info files and installs them.
+
+
+.section Setting up the spool directory
+.index spool directory||creating
+When it starts up, Exim tries to create its spool directory if it does not
+exist. The Exim uid and gid are used for the owner and group of the spool
+directory. Sub-directories are automatically created in the spool directory as
+necessary.
+
+
+
+.section Testing
+.index testing||installation
+Having installed Exim, you can check that the run time configuration file is
+syntactically valid by running the following command, which assumes that the
+Exim binary directory is within your \\PATH\\ environment variable:
+.display
+exim -bV
+.endd
+If there are any errors in the configuration file, Exim outputs error messages.
+Otherwise it outputs the version number and build date,
+the DBM library that is being used, and information about which drivers and
+other optional code modules are included in the binary.
+Some simple routing tests can be done by using the address testing option. For
+example,
+.display
+exim -bt <<local username>>
+.endd
+should verify that it recognizes a local mailbox, and
+.display
+exim -bt <<remote address>>
+.endd
+a remote one. Then try getting it to deliver mail, both locally and remotely.
+This can be done by passing messages directly to Exim, without going through a
+user agent. For example:
+.display
+exim -v postmaster@@your.domain.example
+From: user@@your.domain.example
+To: postmaster@@your.domain.example
+Subject: Testing Exim
+
+This is a test message.
+^D
+.endd
+The \-v-\ option causes Exim to output some verification of what it is doing.
+In this case you should see copies of three log lines, one for the message's
+arrival, one for its delivery, and one containing `Completed'.
+
+.index delivery||problems with
+If you encounter problems, look at Exim's log files (\*mainlog*\ and
+\*paniclog*\) to see if there is any relevant information there. Another source
+of information is running Exim with debugging turned on, by specifying the
+\-d-\ option. If a message is stuck on Exim's spool, you can force a delivery
+with debugging turned on by a command of the form
+.display
+exim -d -M <<message-id>>
+.endd
+You must be root or an `admin user' in order to do this. The \-d-\ option
+produces rather a lot of output, but you can cut this down to specific areas.
+For example, if you use \-d-all+route-\ only the debugging information relevant
+to routing is included. (See the \-d-\ option in chapter ~~CHAPcommandline for
+more details.)
+
+.index `sticky' bit
+.index lock files
+One specific problem that has shown up on some sites is the inability to do
+local deliveries into a shared mailbox directory, because it does not have the
+`sticky bit' set on it. By default, Exim tries to create a lock file before
+writing to a mailbox file, and if it cannot create the lock file, the delivery
+is deferred. You can get round this either by setting the `sticky bit' on the
+directory, or by setting a specific group for local deliveries and allowing
+that group to create files in the directory (see the comments above the
+\%local@_delivery%\ transport in the default configuration file). Another
+approach is to configure Exim not to use lock files, but just to rely on
+\*fcntl()*\ locking instead. However, you should do this only if all user
+agents also use \*fcntl()*\ locking. For further discussion of locking issues,
+see chapter ~~CHAPappendfile.
+
+One thing that cannot be tested on a system that is already running an MTA is
+the receipt of incoming SMTP mail on the standard SMTP port. However, the
+\-oX-\ option can be used to run an Exim daemon that listens on some other
+port, or \*inetd*\ can be used to do this. The \-bh-\ option and the
+\*exim@_checkaccess*\ utility can be used to check out policy controls on
+incoming SMTP mail.
+
+Testing a new version on a system that is already running Exim can most easily
+be done by building a binary with a different \\CONFIGURE@_FILE\\ setting. From
+within the run time configuration, all other file and directory names
+that Exim uses can be altered, in order to keep it entirely clear of the
+production version.
+
+.section Replacing another MTA with Exim
+.index replacing another MTA
+Building and installing Exim for the first time does not of itself put it in
+general use. The name by which the system's MTA is called by mail user agents
+is either \(/usr/sbin/sendmail)\, or \(/usr/lib/sendmail)\ (depending on the
+operating system), and it is necessary to make this name point to the \*exim*\
+binary in order to get the user agents to pass messages to Exim. This is
+normally done by renaming any existing file and making \(/usr/sbin/sendmail)\
+or \(/usr/lib/sendmail)\
+.index symbolic link||to \*exim*\ binary
+a symbolic link to the \*exim*\ binary. It is a good idea to remove any setuid
+privilege and executable status from the old MTA. It is then necessary to stop
+and restart the mailer daemon, if one is running.
+
+.index FreeBSD, MTA indirection
+.index \(/etc/mail/mailer.conf)\
+Some operating systems have introduced alternative ways of switching MTAs. For
+example, if you are running FreeBSD, you need to edit the file
+\(/etc/mail/mailer.conf)\ instead of setting up a symbolic link as just
+described. A typical example of the contents of this file for running Exim is
+as follows:
+.display asis
+sendmail /usr/exim/bin/exim
+send-mail /usr/exim/bin/exim
+mailq /usr/exim/bin/exim -bp
+newaliases /usr/bin/true
+.endd
+
+Once you have set up the symbolic link, or edited \(/etc/mail/mailer.conf)\,
+your Exim installation is `live'. Check it by sending a message from your
+favourite user agent.
+
+You should consider what to tell your users about the change of MTA. Exim may
+have different capabilities to what was previously running, and there are
+various operational differences such as the text of messages produced by
+command line options and in bounce messages. If you allow your users to make
+use of Exim's filtering capabilities, you should make the document entitled
+.if ~~html
+[(A HREF="filter.html")]
+.fi
+\*Exim's interface to mail filtering*\
+.if ~~html
+[(/A)]
+.fi
+available to them.
+
+
+.section Upgrading Exim
+.index upgrading Exim
+If you are already running Exim on your host, building and installing a new
+version automatically makes it available to MUAs, or any other programs that
+call the MTA directly. However, if you are running an Exim daemon, you do need
+to send it a HUP signal, to make it re-exec itself, and thereby pick up the new
+binary. You do not need to stop processing mail in order to install a new
+version of Exim.
+
+
+.section Stopping the Exim daemon on Solaris
+.index Solaris||stopping Exim on
+The standard command for stopping the mailer daemon on Solaris is
+.display
+/etc/init.d/sendmail stop
+.endd
+If \(/usr/lib/sendmail)\ has been turned into a symbolic link, this script
+fails to stop Exim because it uses the command \*ps -e*\ and greps the output
+for the text `sendmail'; this is not present because the actual program name
+(that is, `exim') is given by the \*ps*\ command with these options. A solution
+is to replace the line that finds the process id with something like
+.display asis
+pid=`cat /var/spool/exim/exim-daemon.pid`
+.endd
+to obtain the daemon's pid directly from the file that Exim saves it in.
+
+Note, however, that stopping the daemon does not `stop Exim'. Messages can
+still be received from local processes, and if automatic delivery is configured
+(the normal case), deliveries will still occur.
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The Exim command line
+.set runningfoot "command line"
+.rset CHAPcommandline ~~chapter
+.index command line||options
+.index options||command line
+
+Exim's command line takes the standard Unix form of a sequence of options,
+each starting with a hyphen character, followed by a number of arguments. The
+options are compatible with the main options of Sendmail, and there are also
+some additional options, some of which are compatible with Smail 3. Certain
+combinations of options do not make sense, and provoke an error if used.
+The form of the arguments depends on which options are set.
+
+.section Setting options by program name
+.index \*mailq*\
+If Exim is called under the name \*mailq*\, it behaves as if the option \-bp-\
+were present before any other options.
+The \-bp-\ option requests a listing of the contents of the mail queue on the
+standard output.
+This feature is for compatibility with some systems that contain a command of
+that name in one of the standard libraries, symbolically linked to
+\(/usr/sbin/sendmail)\ or \(/usr/lib/sendmail)\.
+
+.index \*rsmtp*\
+If Exim is called under the name \*rsmtp*\ it behaves as if the option \-bS-\
+were present before any other options, for compatibility with Smail. The \-bS-\
+option is used for reading in a number of messages in batched SMTP format.
+
+.index \*rmail*\
+If Exim is called under the name \*rmail*\ it behaves as if the \-i-\ and
+\-oee-\ options were present before any other options, for compatibility with
+Smail. The name \*rmail*\ is used as an interface by some UUCP systems.
+
+.index \*runq*\
+.index queue runner
+If Exim is called under the name \*runq*\ it behaves as if the option \-q-\ were
+present before any other options, for compatibility with Smail. The \-q-\
+option causes a single queue runner process to be started.
+
+.index \*newaliases*\
+.index alias file||building
+.index Sendmail compatibility||calling Exim as \*newaliases*\
+If Exim is called under the name \*newaliases*\ it behaves as if the option
+\-bi-\ were present before any other options, for compatibility with Sendmail.
+This option is used for rebuilding Sendmail's alias file. Exim does not have
+the concept of a single alias file, but can be configured to run a given
+command if called with the \-bi-\ option.
+
+.section Trusted and admin users
+.rset SECTtrustedadmin "~~chapter.~~section"
+Some Exim options are available only to \*trusted users*\ and others are
+available only to \*admin users*\. In the description below, the phrases `Exim
+user' and `Exim group' mean the user and group defined by \\EXIM@_USER\\ and
+\\EXIM@_GROUP\\ in \(Local/Makefile)\ or set by the \exim@_user\ and
+\exim@_group\ options. These do not necessarily have to use the name `exim'.
+
+.numberpars $.
+.index trusted user||definition of
+.index user||trusted, definition of
+The trusted users are root, the Exim user, any user listed in the
+\trusted@_users\ configuration option, and any user whose current group or any
+supplementary group is one of those listed in the \trusted@_groups\
+configuration option. Note that the Exim group is not automatically trusted.
+
+.index `From' line
+.index envelope sender
+Trusted users are always permitted to use the \-f-\ option or a leading `From '
+line to specify the envelope sender of a message that is passed to Exim through
+the local interface (see the \-bm-\ and \-f-\ options below). See the
+\untrusted@_set@_sender\ option for a way of permitting non-trusted users to
+set envelope senders.
+.index ::From:: header line
+.index ::Sender:: header line
+For a trusted user, there is never any check on the contents of the ::From::
+header line, and a ::Sender:: line is never added. Furthermore, any existing
+::Sender:: line in incoming local (non-TCP/IP) messages is not removed.
+
+Trusted users may also specify a host name, host address, interface address,
+protocol name, ident value, and authentication data when submitting a message
+locally. Thus, they are able to insert messages into Exim's queue locally that
+have the characteristics of messages received from a remote host. Untrusted
+users may in some circumstances use \-f-\, but can never set the other values
+that are available to trusted users.
+.nextp
+.index user||admin, definition of
+.index admin user||definition of
+The admin users are root, the Exim user, and any user that is a member of the
+Exim group or of any group listed in the \admin@_groups\ configuration option.
+The current group does not have to be one of these groups.
+
+Admin users are permitted to list the queue, and to carry out certain
+operations on messages, for example, to force delivery failures. It is also
+necessary to be an admin user in order to see the full information provided by
+the Exim monitor, and full debugging output.
+
+By default, the use of the \-M-\, \-q-\, \-R-\, and \-S-\ options to cause Exim
+to attempt delivery of messages on its queue is restricted to admin users.
+However, this restriction can be relaxed by setting the \prod@_requires@_admin\
+option false (that is, specifying \no@_prod@_requires@_admin\).
+
+Similarly, the use of the \-bp-\ option to list all the messages in the queue
+is restricted to admin users unless \queue@_list@_requires@_admin\ is set
+false.
+.endp
+
+\**Warning**\: If you configure your system so that admin users are able to
+edit Exim's configuration file, you are giving those users an easy way of
+getting root. There is further discussion of this issue at the start of chapter
+~~CHAPconf.
+
+
+
+.section Command line options
+The command options are described in alphabetical order below.
+
+.startoptions
+
+.option @-
+.index options||command line, terminating
+This is a pseudo-option whose only purpose is to terminate the options and
+therefore to cause subsequent command line items to be treated as arguments
+rather than options, even if they begin with hyphens.
+
+.option -help
+This option causes Exim to output a few sentences stating what it is.
+The same output is generated if the Exim binary is called with no options and
+no arguments.
+
+.option B <<type>>
+.index 8-bit characters
+.index Sendmail compatibility||8-bit characters
+This is a Sendmail option for selecting 7 or 8 bit processing. Exim is 8-bit
+clean; it ignores this option.
+
+.option bd
+.index daemon
+.index SMTP listener
+.index queue runner
+This option runs Exim as a daemon, awaiting incoming SMTP connections. Usually
+the \-bd-\ option is combined with the \-q-\<<time>> option, to specify that
+the daemon should also initiate periodic queue runs.
+
+The \-bd-\ option can be used only by an admin user. If either of the \-d-\
+(debugging) or \-v-\ (verifying) options are set, the daemon does not
+disconnect from the controlling terminal. When running this way, it can be
+stopped by pressing ctrl-C.
+
+By default, Exim listens for incoming connections to the standard SMTP port on
+all the host's running interfaces. However, it is possible to listen on other
+ports, on multiple ports, and only on specific interfaces. Chapter
+~~CHAPinterfaces contains a description of the options that control this.
+
+.index daemon||process id (pid)
+.index pid (process id)||of daemon
+When a listening daemon is started without the use of \-oX-\ (that is, without
+overriding the normal configuration), it writes its process id to a file called
+\(exim-daemon.pid)\ in Exim's spool directory. This location can be overridden
+by setting \\PID@_FILE@_PATH\\ in \(Local/Makefile)\. The file is written while
+Exim is still running as root.
+
+When \-oX-\ is used on the command line to start a listening daemon, the
+process id is not written to the normal pid file path. However, \-oP-\ can be
+used to specify a path on the command line if a pid file is required.
+
+.index \\SIGHUP\\
+The \\SIGHUP\\ signal can be used to cause the daemon to re-exec itself. This
+should be done whenever Exim's configuration file, or any file that is
+incorporated into it by means of the \.include\ facility, is changed, and also
+whenever a new version of Exim is installed. It is not necessary to do this
+when other files that are referenced from the configuration (for example, alias
+files) are changed, because these are reread each time they are used.
+
+.option bdf
+This option has the same effect as \-bd-\ except that it never disconnects from
+the controlling terminal, even when no debugging is specified.
+
+.option be
+.index testing||string expansion
+.index expansion||testing
+Run Exim in expansion testing mode. Exim discards its root privilege, to
+prevent ordinary users from using this mode to read otherwise inaccessible
+files. If no arguments are given, Exim runs interactively, prompting for lines
+of data. Long expressions can be split over several lines by using backslash
+continuations.
+As in Exim's run time configuration, whitespace at the start of continuation
+lines is ignored.
+
+Each argument or data line is passed through the string expansion mechanism,
+and the result is output. Variable values from the configuration file (for
+example, \$qualify@_domain$\) are available, but no message-specific values
+(such as \$domain$\) are set, because no message is being processed.
+
+.option bF #<<filename>>
+.index system filter||testing
+.index testing||system filter
+This option is the same as \-bf-\ except that it assumes that the filter being
+tested is a system filter. The additional commands that are available only in
+system filters are recognized.
+
+.option bf #<<filename>>
+.index filter||testing
+.index testing||filter file
+.index forward file||testing
+.index testing||forward file
+.index Sieve filter||testing
+This option runs Exim in filter testing mode; the file is the filter file to be
+tested, and a test message must be supplied on the standard input. If there are
+no message-dependent tests in the filter, an empty file can be supplied. If a
+system filter file is being tested, \-bF-\ should be used instead of \-bf-\. If
+the test file does not begin with
+one of the special lines
+.display asis
+# Exim filter
+# Sieve filter
+.endd
+it is taken to be a normal \(.forward)\ file, and is tested for validity under
+that interpretation. See sections ~~SECTitenonfilred to ~~SECTspecitredli for a
+description of the possible contents of non-filter redirection lists.
+
+The result of an Exim command that uses \-bf-\, provided no errors are
+detected, is a list of the actions that Exim would try to take if presented
+with the message for real. More details of filter testing are given in the
+separate document entitled \*Exim's interfaces to mail filtering*\.
+
+.index `From' line
+.index envelope sender
+.index \-f-\ option||for filter testing
+When testing a filter file, the envelope sender can be set by the \-f-\ option,
+or by a `From ' line at the start of the test message. Various parameters that
+would normally be taken from the envelope recipient address of the message can
+be set by means of additional command line options. These are:
+.display rm
+.if ~~sys.fancy
+.tabset 12em 16em
+.else
+.tabset 15em 20em
+.fi
+. The odd alignment here gets it lined up in the man page.
+\-bfd-\ $t <<domain>> $t $rm{default is the qualify domain}
+\-bfl-\ $t <<local@_part>> $t $rm{default is the logged in user}
+\-bfp-\ $t <<local@_part@_prefix>> $t $rm{default is null}
+\-bfs-\ $t <<local@_part@_suffix>> $t $rm{default is null}
+.endd
+The local part should always be set to the incoming address with any prefix or
+suffix stripped, because that is how it appears to the filter when a message is
+actually being delivered.
+
+.option bh #<<IP address>>
+.index testing||incoming SMTP
+.index SMTP||testing incoming
+.index testing||relay control
+.index relaying||testing configuration
+.index policy control||testing
+.index debugging||\-bh-\ option
+This option runs a fake SMTP session as if from the given IP address, using the
+standard input and output. The IP address may include a port number at the end,
+after a full stop. For example:
+.display asis
+exim -bh 10.9.8.7.1234
+exim -bh fe80::a00:20ff:fe86:a061.5678
+.endd
+Comments as to what is going on are written to the standard error file. These
+include lines beginning with `LOG' for anything that would have been logged.
+This facility is provided for testing configuration options for incoming
+messages, to make sure they implement the required policy. For example, you can
+test your relay controls using \-bh-\.
+
+.index RFC 1413
+\**Warning 1**\: You cannot test features of the configuration that rely on
+ident (RFC 1413) callouts. These cannot be done when testing using
+\-bh-\ because there is no incoming SMTP connection.
+
+\**Warning 2**\: Address verification callouts (see section ~~SECTcallver) are
+also skipped when testing using \-bh-\. If you want these callouts to occur,
+use \-bhc-\ instead.
+
+Messages supplied during the testing session are discarded, and nothing is
+written to any of the real log files. There may be pauses when DNS (and other)
+lookups are taking place, and of course these may time out. The \-oMi-\ option
+can be used to specify a specific IP interface and port if this is important.
+
+The \*exim@_checkaccess*\ utility is a `packaged' version of \-bh-\ whose
+output just states whether a given recipient address from a given host is
+acceptable or not. See section ~~SECTcheckaccess.
+
+.option bhc #<<IP address>>
+This option operates in the same way as \-bh-\, except that address
+verification callouts are performed if required. This includes consulting and
+updating the callout cache database.
+
+.option bi
+.index alias file||building
+.index building alias file
+.index Sendmail compatibility||\-bi-\ option
+Sendmail interprets the \-bi-\ option as a request to rebuild its alias file.
+Exim does not have the concept of a single alias file, and so it cannot mimic
+this behaviour. However, calls to \(/usr/lib/sendmail)\ with the \-bi-\ option
+tend to appear in various scripts such as NIS make files, so the option must be
+recognized.
+
+If \-bi-\ is encountered, the command specified by the \bi@_command\
+configuration option is run, under the uid and gid of the caller of Exim. If
+the \-oA-\ option is used, its value is passed to the command as an argument.
+The command set by \bi@_command\ may not contain arguments. The command can use
+the \*exim@_dbmbuild*\ utility, or some other means, to rebuild alias files if
+this is required. If the \bi@_command\ option is not set, calling Exim with
+\-bi-\ is a no-op.
+
+.option bm
+.index local message reception
+This option runs an Exim receiving process that accepts an incoming,
+locally-generated message on the current input. The recipients are given as the
+command arguments (except when \-t-\ is also present -- see below). Each
+argument can be a comma-separated list of RFC 2822 addresses. This is the
+default option for selecting the overall action of an Exim call; it is assumed
+if no other conflicting option is present.
+
+If any addresses in the message are unqualified (have no domain), they are
+qualified by the values of the \qualify@_domain\ or \qualify@_recipient\
+options, as appropriate. The \-bnq-\ option (see below) provides a way of
+suppressing this for special cases.
+
+Policy checks on the contents of local messages can be enforced by means of the
+non-SMTP ACL. See chapter ~~CHAPACL for details.
+.index return code||for \-bm-\
+The return code is zero if the message is successfully accepted. Otherwise, the
+action is controlled by the \-oe$it{x}-\ option setting -- see below.
+
+.index message||format
+.index format||message
+.index `From' line
+.index UUCP||`From' line
+.index Sendmail compatibility||`From' line
+The format of the message must be as defined in RFC 2822, except that, for
+compatibility with Sendmail and Smail, a line in one of the forms
+.display
+From sender Fri Jan 5 12:55 GMT 1997
+From sender Fri, 5 Jan 97 12:55:01
+.endd
+(with the weekday optional, and possibly with additional text after the date)
+is permitted to appear at the start of the message. There appears to be no
+authoritative specification of the format of this line. Exim recognizes it by
+matching against the regular expression defined by the \uucp@_from@_pattern\
+option, which can be changed if necessary.
+.index \-f-\ option||overriding `From' line
+The specified sender is treated as if it were given as the argument to the
+\-f-\ option, but if a \-f-\ option is also present, its argument is used in
+preference to the address taken from the message. The caller of Exim must be a
+trusted user for the sender of a message to be set in this way.
+
+.option bnq
+.index address||qualification, suppressing
+By default, Exim automatically qualifies unqualified addresses (those
+without domains) that appear in messages that are submitted locally (that
+is, not over TCP/IP). This qualification applies both to addresses in
+envelopes, and addresses in header lines. Sender addresses are qualified using
+\qualify@_domain\, and recipient addresses using \qualify@_recipient\ (which
+defaults to the value of \qualify@_domain\).
+
+Sometimes, qualification is not wanted. For example, if \-bS-\ (batch SMTP) is
+being used to re-submit messages that originally came from remote hosts after
+content scanning, you probably do not want to qualify unqualified addresses in
+header lines. (Such lines will be present only if you have not enabled a header
+syntax check in the appropriate ACL.)
+
+The \-bnq-\ option suppresses all qualification of unqualified addresses in
+messages that originate on the local host. When this is used, unqualified
+addresses in the envelope provoke errors (causing message rejection) and
+unqualified addresses in header lines are left alone.
+
+
+.option bP
+.index configuration options, extracting
+.index options||configuration, extracting
+If this option is given with no arguments, it causes the values of all Exim's
+main configuration options to be written to the standard output. The values
+of one or more specific options can be requested by giving their names as
+arguments, for example:
+.display
+exim -bP qualify@_domain hold@_domains
+.endd
+However, any option setting that is preceded by the word `hide' in the
+configuration file is not shown in full, except to an admin user. For other
+users, the output is as in this example:
+.display asis
+mysql_servers = <value not displayable>
+.endd
+If \configure@_file\ is given as an argument, the name of the run time
+configuration file is output.
+If a list of configuration files was supplied, the value that is output here
+is the name of the file that was actually used.
+
+.index daemon||process id (pid)
+.index pid (process id)||of daemon
+If \log__file__path\ or \pid@_file@_path\ are given, the names of the
+directories where log files and daemon pid files are written are output,
+respectively. If these values are unset, log files are written in a
+sub-directory of the spool directory called \log\, and the pid file is written
+directly into the spool directory.
+
+If \-bP-\ is followed by a name preceded by \"+"\, for example,
+.display asis
+exim -bP +local_domains
+.endd
+it searches for a matching named list of any type (domain, host, address, or
+local part) and outputs what it finds.
+
+.index options||router, extracting
+.index options||transport, extracting
+If one of the words \router\, \transport\, or \authenticator\ is given,
+followed by the name of an appropriate driver instance, the option settings for
+that driver are output. For example:
+.display
+exim -bP transport local@_delivery
+.endd
+The generic driver options are output first, followed by the driver's private
+options. A list of the names of drivers of a particular type can be obtained by
+using one of the words \router@_list\, \transport@_list\, or
+\authenticator@_list\, and a complete list of all drivers with their option
+settings can be obtained by using \routers\, \transports\, or \authenticators\.
+
+
+.option bp
+.index queue||listing messages on
+.index listing||messages on the queue
+This option requests a listing of the contents of the mail queue on the
+standard output. If the \-bp-\ option is followed by a list of message ids,
+just those messages are listed. By default, this option can be used only by an
+admin user. However, the \queue__list__requires__admin\ option can be set false
+to allow any user to see the queue.
+
+Each message on the queue is displayed as in the following example:
+.display
+25m 2.9K 0t5C6f-0000c8-00 <alice@@wonderland.fict.example>
+ red.king@@looking-glass.fict.example
+ <<other addresses>>
+.endd
+.index message||size in queue listing
+.index size||of message
+The first line contains the length of time the message has been on the queue
+(in this case 25 minutes), the size of the message (2.9K), the unique local
+identifier for the message, and the message sender, as contained in the
+envelope. For bounce messages, the sender address is empty, and appears as
+`<>'. If the message was submitted locally by an untrusted user who overrode
+the default sender address, the user's login name is shown in parentheses
+before the sender address.
+.index frozen messages||in queue listing
+If the message is frozen (attempts to deliver it are suspended) then the text
+`$*$$*$$*$ frozen $*$$*$$*$' is displayed at the end of this line.
+
+The recipients of the message (taken from the envelope, not the headers) are
+displayed on subsequent lines. Those addresses to which the message has already
+been delivered are marked with the letter D. If an original address gets
+expanded into several addresses via an alias or forward file, the original is
+displayed with a D only when deliveries for all of its child addresses are
+complete.
+
+
+.option bpa
+This option operates like \-bp-\, but in addition it shows delivered addresses
+that were generated from the original top level address(es) in each message by
+alias or forwarding operations. These addresses are flagged with `+D' instead
+of just `D'.
+
+
+.option bpc
+.index queue||count of messages on
+This option counts the number of messages on the queue, and writes the total
+to the standard output. It is restricted to admin users, unless
+\queue__list__requires__admin\ is set false.
+
+
+.option bpr
+This option operates like \-bp-\, but the output is not sorted into
+chronological order of message arrival. This can speed it up when there are
+lots of messages on the queue, and is particularly useful if the output is
+going to be post-processed in a way that doesn't need the sorting.
+
+.option bpra
+This option is a combination of \-bpr-\ and \-bpa-\.
+
+.option bpru
+This option is a combination of \-bpr-\ and \-bpu-\.
+
+
+.option bpu
+This option operates like \-bp-\ but shows only undelivered top-level addresses
+for each message displayed. Addresses generated by aliasing or forwarding are
+not shown, unless the message was deferred after processing by a router with
+the \one@_time\ option set.
+
+
+.option brt
+.index testing||retry configuration
+.index retry||configuration testing
+This option is for testing retry rules, and it must be followed by up to three
+arguments. It causes Exim to look for a retry rule that matches the values
+and to write it to the standard output. For example:
+.display asis
+exim -brt bach.comp.mus.example
+Retry rule: *.comp.mus.example F,2h,15m; F,4d,30m;
+.endd
+See chapter ~~CHAPretry for a description of Exim's retry rules. The first
+argument, which is required, can be a complete address in the form
+\*local@_part@@domain*\, or it can be just a domain name. The second argument is
+an optional second domain name; if no retry rule is found for the first
+argument, the second is tried. This ties in with Exim's behaviour when looking
+for retry rules for remote hosts -- if no rule is found that matches the host,
+one that matches the mail domain is sought. The final argument is the name of a
+specific delivery error, as used in setting up retry rules, for example
+`quota@_3d'.
+
+.option brw
+.index testing||rewriting
+.index rewriting||testing
+This option is for testing address rewriting rules, and it must be followed by
+a single argument, consisting of either a local part without a domain, or a
+complete address with a fully qualified domain. Exim outputs how this address
+would be rewritten for each possible place it might appear. See chapter
+~~CHAPrewrite for further details.
+
+.option bS
+.index SMTP||batched incoming
+.index batched SMTP input
+This option is used for batched SMTP input, which is an alternative interface
+for non-interactive local message submission. A number of messages can be
+submitted in a single run. However, despite its name, this is not really SMTP
+input. Exim reads each message's envelope from SMTP commands on the standard
+input, but generates no responses. If the caller is trusted, or
+\untrusted@_set@_sender\ is set, the senders in the SMTP \\MAIL\\ commands are
+believed; otherwise the sender is always the caller of Exim.
+
+The message itself is read from the standard input, in SMTP format (leading
+dots doubled), terminated by a line containing just a single dot. An error is
+provoked if the terminating dot is missing. A further message may then follow.
+
+As for other local message submissions, the contents of incoming batch SMTP
+messages can be checked using the non-SMTP ACL (see chapter ~~CHAPACL).
+Unqualified addresses are automatically qualified using \qualify@_domain\ and
+\qualify@_recipient\, as appropriate, unless the \-bnq-\ option is used.
+
+Some other SMTP commands are recognized in the input. \\HELO\\ and \\EHLO\\ act
+as \\RSET\\; \\VRFY\\, \\EXPN\\, \\ETRN\\, and \\HELP\\ act as \\NOOP\\;
+\\QUIT\\ quits, ignoring the rest of the standard input.
+
+If any error is encountered, reports are written to the standard output and
+error streams, and Exim gives up immediately.
+.index return code||for \-bS-\
+The return code is 0 if no error was detected; it is 1 if one or more messages
+were accepted before the error was detected; otherwise it is 2.
+
+More details of input using batched SMTP are given in section
+~~SECTincomingbatchedSMTP.
+
+.option bs
+.index SMTP||local input
+.index local SMTP input
+This option causes Exim to accept one or more messages by reading SMTP commands
+on the standard input, and producing SMTP replies on the standard output. SMTP
+policy controls, as defined in ACLs (see chapter ~~CHAPACL) are applied.
+
+Some user agents use this interface as a way of passing locally-generated
+messages to the MTA.
+.index sender||source of
+In this usage, if the caller of Exim is trusted, or \untrusted@_set@_sender\ is
+set, the senders of messages are taken from the SMTP \\MAIL\\ commands.
+Otherwise the content of these commands is ignored and the sender is set up as
+the calling user. Unqualified addresses are automatically qualified using
+\qualify@_domain\ and \qualify@_recipient\, as appropriate, unless the \-bnq-\
+option is used.
+
+.index inetd
+The \-bs-\ option is also used to run Exim from \*inetd*\, as an alternative to
+using a listening daemon. Exim can distinguish the two cases by checking
+whether the standard input is a TCP/IP socket. When Exim is called from
+\*inetd*\, the source of the mail is assumed to be remote, and the comments
+above concerning senders and qualification do not apply. In this situation,
+Exim behaves in exactly the same way as it does when receiving a message via
+the listening daemon.
+
+.option bt
+.index testing||addresses
+.index address||testing
+This option runs Exim in address testing mode, in which each argument is taken
+as an address to be tested for deliverability. The results are written to the
+standard output.
+If a test fails, and the caller is not an admin user, no details of the
+failure are output, because these might contain sensitive information such as
+usernames and passwords for database lookups.
+
+If no arguments are given, Exim runs in an interactive manner, prompting with a
+right angle bracket for addresses to be tested. Each address is handled as if
+it were the recipient address of a message (compare the \-bv-\ option). It is
+passed to the routers and the result is written to the standard output.
+However, any router that has \no@_address@_test\ set is bypassed. This can
+make \-bt-\ easier to use for genuine routing tests if your first router passes
+everything to a scanner program.
+
+.index return code||for \-bt-\
+The return code is 2 if any address failed outright; it is 1 if no address
+failed outright but at least one could not be resolved for some reason. Return
+code 0 is given only when all addresses succeed.
+
+\**Warning**\: \-bt-\ can only do relatively simple testing. If any of the
+routers in the configuration makes any tests on the sender address of a
+message,
+.index \-f-\ option||for address testing
+you can use the \-f-\ option to set an appropriate sender when running
+\-bt-\ tests. Without it, the sender is assumed to be the calling user at the
+default qualifying domain. However, if you have set up (for example) routers
+whose behaviour depends on the contents of an incoming message, you cannot test
+those conditions using \-bt-\. The \-N-\ option provides a possible way of
+doing such tests.
+
+.option bV
+.index version number of Exim, verifying
+This option causes Exim to write the current version number, compilation
+number, and compilation date of the \*exim*\ binary to the standard output.
+It also lists the DBM library this is being used, the optional modules (such as
+specific lookup types), the drivers that are included in the binary, and the
+name of the run time configuration file that is in use.
+
+.option bv
+.index verifying||address, using \-bv-\
+.index address||verification
+This option runs Exim in address verification mode, in which each argument is
+taken as an address to be verified. During normal operation, verification
+happens mostly as a consequence processing a \verify\ condition in an ACL (see
+chapter ~~CHAPACL). If you want to test an entire ACL, see the \-bh-\ option.
+
+If verification fails, and the caller is not an admin user, no details of the
+failure are output, because these might contain sensitive information such as
+usernames and passwords for database lookups.
+
+If no arguments are given, Exim runs in an interactive manner, prompting with a
+right angle bracket for addresses to be verified. Verification differs from
+address testing (the \-bt-\ option) in that routers that have \no@_verify\ set
+are skipped, and if the address is accepted by a router that has \fail@_verify\
+set, verification fails. The address is verified as a recipient if \-bv-\ is
+used; to test verification for a sender address, \-bvs-\ should be used.
+
+If the \-v-\ option is not set, the output consists of a single line for each
+address, stating whether it was verified or not, and giving a reason in the
+latter case. Otherwise, more details are given of how the address has been
+handled, and in the case of address redirection, all the generated addresses
+are also considered. Without \-v-\, generating more than one address by
+redirection causes verification to end sucessfully.
+
+.index return code||for \-bv-\
+The return code is 2 if any address failed outright; it is 1 if no address
+failed outright but at least one could not be resolved for some reason. Return
+code 0 is given only when all addresses succeed.
+
+If any of the routers in the configuration makes any tests on the sender
+address of a message, you should use the \-f-\ option to set an appropriate
+sender when running \-bv-\ tests. Without it, the sender is assumed to be the
+calling user at the default qualifying domain.
+
+.option bvs
+This option acts like \-bv-\, but verifies the address as a sender rather
+than a recipient address. This affects any rewriting and qualification that
+might happen.
+
+.option C #<<filelist>>
+.index configuration file||alternate
+.index \\CONFIGURE@_FILE\\
+.index alternate configuration file
+This option causes Exim to find the run time configuration file from the given
+list instead of from the list specified by the \\CONFIGURE@_FILE\\
+compile-time setting. Usually, the list will consist of just a single file
+name, but it can be a colon-separated list of names. In this case, the first
+file that exists is used. Failure to open an existing file stops Exim from
+proceeding any further along the list, and an error is generated.
+
+When this option is used by a caller other than root or the Exim user,
+and the list is different from the compiled-in list, Exim gives up
+its root privilege immediately, and runs with the real and effective uid and
+gid set to those of the caller.
+However, if \\ALT@_CONFIG@_ROOT@_ONLY\\ is defined in \(Local/Makefile)\, root
+privilege is retained for \-C-\ only if the caller of Exim is root.
+This option is not set by default.
+
+Setting \\ALT@_CONFIG@_ROOT@_ONLY\\ locks out the possibility of testing a
+configuration using \-C-\ right through message reception and delivery, even if
+the caller is root. The reception works, but by that time, Exim is running as
+the Exim user, so when it re-execs to regain privilege for the delivery, the
+use of \-C-\ causes privilege to be lost. However, root can test reception and
+delivery using two separate commands (one to put a message on the queue, using
+\-odq-\, and another to do the delivery, using \-M-\).
+
+If \\ALT@_CONFIG@_PREFIX\\ is defined \(in Local/Makefile)\, it specifies a
+prefix string with which any file named in a \-C-\ command line option
+must start. In addition, the file name must not contain the sequence \"/../"\.
+However, if the value of the \-C-\ option is identical to the value of
+\\CONFIGURE@_FILE\\ in \(Local/Makefile)\, Exim ignores \-C-\ and proceeds as
+usual. There is no default setting for \\ALT@_CONFIG@_PREFIX\\; when it is
+unset, any file name can be used with \-C-\.
+
+\\ALT@_CONFIG@_PREFIX\\ can be used to confine alternative configuration files
+to a directory to which only root has access. This prevents someone who has
+broken into the Exim account from running a privileged Exim with an arbitrary
+configuration file.
+
+The \-C-\ facility is useful for ensuring that configuration files are
+syntactically correct, but cannot be used for test deliveries, unless the
+caller is privileged, or unless it is an exotic configuration that does not
+require privilege. No check is made on the owner or group of the files
+specified by this option.
+
+.option D <<macro>>=<<value>>
+.index macro||setting on command line
+This option can be used to override macro definitions in the configuration file
+(see section ~~SECTmacrodefs). However, like \-C-\, if it is used by an
+unprivileged caller, it causes Exim to give up its root privilege.
+If \\DISABLE@_D@_OPTION\\ is defined in \(Local/Makefile)\, the use of \-D-\ is
+completely disabled, and its use causes an immediate error exit.
+
+The entire option (including equals sign if present) must all be within one
+command line item. \-D-\ can be used to set the value of a macro to the empty
+string, in which case the equals sign is optional. These two commands are
+synonymous:
+.display asis
+exim -DABC ...
+exim -DABC= ...
+.endd
+To include spaces in a macro definition item, quotes must be used. If you use
+quotes, spaces are permitted around the macro name and the equals sign. For
+example:
+.display asis
+exim '-D ABC = something' ...
+.endd
+\-D-\ may be repeated up to 10 times on a command line.
+
+.option d <<debug options>>
+.index debugging||list of selectors
+.index debugging||\-d-\ option
+This option causes debugging information to be written to the standard
+error stream. It is restricted to admin users because debugging output may show
+database queries that contain password information. Also, the details of users'
+filter files should be protected. When \-d-\ is used, \-v-\ is assumed. If
+\-d-\ is given on its own, a lot of standard debugging data is output. This can
+be reduced, or increased to include some more rarely needed information, by
+following \-d-\ with a string made up of names preceded by plus or minus
+characters. These add or remove sets of debugging data, respectively. For
+example, \-d+filter-\ adds filter debugging, whereas \-d-all+filter-\ selects
+only filter debugging. The available debugging categories are:
+.display flow
+.tabs 21
+.
+. The odd formatting of the lines below is deliberate. It does not affect the
+. SGCAL output, but by putting in the space it keeps things aligned in the man
+. page that is automatically generated from this text.
+.
+acl $t $rm{ACL interpretation}
+auth $t $rm{authenticators}
+deliver $t $rm{general delivery logic}
+dns $t $rm{DNS lookups (see also resolver)}
+dnsbl $t $rm{DNS black list (aka RBL) code}
+exec $t $rm{arguments for \execv@(@)\ calls}
+expand $t $rm{detailed debugging for string expansions}
+filter $t $rm{filter handling}
+hints@_lookup $t $rm{hints data lookups}
+host@_lookup $t $rm{all types of name-to-IP address handling}
+ident $t $rm{ident lookup}
+interface $t $rm{lists of local interfaces}
+lists $t $rm{matching things in lists}
+load $t $rm{system load checks}
+local@_scan $t $rm{can be used by \*local@_scan()*\ (see chapter ~~CHAPlocalscan)}
+lookup $t $rm{general lookup code and all lookups}
+memory $t $rm{memory handling}
+pid $t $rm{add pid to debug output lines}
+process@_info $t $rm{setting info for the process log}
+queue@_run $t $rm{queue runs}
+receive $t $rm{general message reception logic}
+resolver $t $rm{turn on the DNS resolver's debugging output}
+retry $t $rm{retry handling}
+rewrite $t $rm{address rewriting}
+route $t $rm{address routing}
+timestamp $t $rm{add timestamp to debug output lines}
+tls $t $rm{TLS logic}
+transport $t $rm{transports}
+uid $t $rm{changes of uid/gid and looking up uid/gid}
+verify $t $rm{address verification logic}
+
+all $t $rm{all of the above, and also \-v-\}
+.endd
+.em
+.index resolver, debugging output
+.index DNS||resolver, debugging output
+The \"resolver"\ option produces output only if the DNS resolver was compiled
+with \\DEBUG\\ enabled. This is not the case in some operating systems. Also,
+unfortunately, debugging output from the DNS resolver is written to stdout
+rather than stderr.
+.nem
+
+The default (\-d-\ with no argument) omits \"expand"\, \"filter"\,
+\"interface"\, \"load"\, \"memory"\, \"pid"\, \"resolver"\, and \"timestamp"\.
+However, the \"pid"\ selector is forced when debugging is turned on for a
+daemon, which then passes it on to any re-executed Exims. Exim also
+automatically adds the pid to debug lines when several remote deliveries are
+run in parallel.
+
+The \"timestamp"\ selector causes the current time to be inserted at the start
+of all debug output lines. This can be useful when trying to track down delays
+in processing.
+
+If the \debug@_print\ option is set in any driver, it produces output whenever
+any debugging is selected, or if \-v-\ is used.
+
+.option dropcr
+This is an obsolete option that is now a no-op. It used to affect the way Exim
+handled CR and LF characters in incoming messages. What happens now is
+described in section ~~SECTlineendings.
+
+
+.option E
+.index bounce message||generating
+This option specifies that an incoming message is a locally-generated delivery
+failure report. It is used internally by Exim when handling delivery failures
+and is not intended for external use. Its only effect is to stop Exim
+generating certain messages to the postmaster, as otherwise message cascades
+could occur in some situations. As part of the same option, a message id may
+follow the characters \-E-\. If it does, the log entry for the receipt of the
+new message contains the id, following `R=', as a cross-reference.
+
+.option e$it{x}
+There are a number of Sendmail options starting with \-oe-\ which seem to be
+called by various programs without the leading \o\ in the option. For example,
+the \vacation\ program uses \-eq-\. Exim treats all options of the form
+\-e$it{x}-\ as synonymous with the corresponding \-oe$it{x}-\ options.
+
+.option F #<<string>>
+.index sender||name
+.index name||of sender
+This option sets the sender's full name for use when a locally-generated
+message is being accepted. In the absence of this option, the user's \*gecos*\
+entry from the password data is used. As users are generally permitted to alter
+their \*gecos*\ entries, no security considerations are involved. White space
+between \-F-\ and the <<string>> is optional.
+
+.option f #<<address>>
+.index sender||address
+.index address||sender
+.index trusted user
+.index envelope sender
+.index user||trusted
+This option sets the address of the envelope sender of a locally-generated
+message (also known as the return path). The option can normally be used only
+by a trusted user, but \untrusted@_set@_sender\ can be set to allow untrusted
+users to use it. In the absence of \-f-\, or if the caller is not allowed to
+use it, the sender of a local message is set to the caller's login name at the
+default qualify domain.
+
+There is one exception to the restriction on the use of \-f-\: an empty sender
+can be specified by any user, to create a message that can never provoke a
+bounce. An empty sender can be specified either as an empty string, or as a
+pair of angle brackets with nothing between them, as in these examples of shell
+commands:
+.display asis
+exim -f '<>' user@domain
+exim -f "" user@domain
+.endd
+In addition, the use of \-f-\ is not restricted when testing a filter file with
+\-bf-\ or when testing or verifying addresses using the \-bt-\ or \-bv-\
+options.
+
+Allowing untrusted users to change the sender address does not of itself make
+it possible to send anonymous mail. Exim still checks that the ::From:: header
+refers to the local user, and if it does not, it adds a ::Sender:: header,
+though this can be overridden by setting \no@_local@_from@_check\.
+
+.index `From' line
+White space between \-f-\ and the <<address>> is optional
+(that is, they can be given as two arguments or one combined argument).
+The sender of a locally-generated message can also be set (when permitted) by
+an initial `From ' line in the message -- see the description of \-bm-\ above
+-- but if \-f-\ is also present, it overrides `From'.
+
+.option G
+.index Sendmail compatibility||\-G-\ option ignored
+This is a Sendmail option which is ignored by Exim.
+
+.option h #<<number>>
+.index Sendmail compatibility||\-h-\ option ignored
+This option is accepted for compatibility with Sendmail, but has no effect. (In
+Sendmail it overrides the `hop count' obtained by counting ::Received::
+headers.)
+
+.option i
+.index Solaris||\*mail*\ command
+.index dot||in incoming, non-SMTP message
+This option, which has the same effect as \-oi-\, specifies that a dot on a
+line by itself should not terminate an incoming, non-SMTP message. I can find
+no documentation for this option in Solaris 2.4 Sendmail, but the \*mailx*\
+command in Solaris 2.4 uses it. See also \-ti-\.
+
+.option M #<<message id>>#<<message id>> ...
+.index forcing delivery
+.index delivery||forcing attempt
+.index frozen messages||forcing delivery
+This option requests Exim to run a delivery attempt on each message in turn. If
+any of the messages are frozen, they are automatically thawed before the
+delivery attempt. The settings of \queue@_domains\, \queue@_smtp@_domains\, and
+\hold@_domains\ are ignored.
+.index hints database||overriding retry hints
+Retry hints for any of the addresses are
+overridden -- Exim tries to deliver even if the normal retry time has not yet
+been reached. This option requires the caller to be an admin user. However,
+there is an option called \prod@_requires@_admin\ which can be set false to
+relax this restriction (and also the same requirement for the \-q-\, \-R-\, and
+\-S-\ options).
+
+
+.option Mar #<<message id>>#<<address>>#<<address>> ...
+.index message||adding recipients
+.index recipient||adding
+This option requests Exim to add the addresses to the list of recipients of the
+message (`ar' for `add recipients'). The first argument must be a message id,
+and the remaining ones must be email addresses. However, if the message is
+active (in the middle of a delivery attempt), it is not altered. This option
+can be used only by an admin user.
+
+.index SMTP||passed connection
+.index SMTP||multiple deliveries
+.index multiple SMTP deliveries
+.option MC #<<transport>>#<<hostname>>#<<sequence number>>#<<message id>>
+This option is not intended for use by external callers. It is used internally
+by Exim to invoke another instance of itself to deliver a waiting message using
+an existing SMTP connection, which is passed as the standard input. Details are
+given in chapter ~~CHAPSMTP. This must be the final option, and the caller must
+be root or the Exim user in order to use it.
+
+.option MCA
+This option is not intended for use by external callers. It is used internally
+by Exim in conjunction with the \-MC-\ option. It signifies that the connection
+to the remote host has been authenticated.
+
+.option MCP
+This option is not intended for use by external callers. It is used internally
+by Exim in conjunction with the \-MC-\ option. It signifies that the server to
+which Exim is connected supports pipelining.
+
+.option MCQ #<<process id>> <<pipe fd>>
+This option is not intended for use by external callers. It is used internally
+by Exim in conjunction with the \-MC-\ option when the original delivery was
+started by a queue runner. It passes on the process id of the queue runner,
+together with the file descriptor number of an open pipe. Closure of the pipe
+signals the final completion of the sequence of processes that are passing
+messages through the same SMTP connection.
+
+.option MCS
+This option is not intended for use by external callers. It is used internally
+by Exim in conjunction with the \-MC-\ option, and passes on the fact that the
+SMTP \\SIZE\\ option should be used on messages delivered down the existing
+connection.
+
+.option MCT
+This option is not intended for use by external callers. It is used internally
+by Exim in conjunction with the \-MC-\ option, and passes on the fact that the
+host to which Exim is connected supports TLS encryption.
+
+.option Mc #<<message id>>#<<message id>> ...
+.index hints database||not overridden by \-Mc-\
+.index delivery||manually started, not forced
+This option requests Exim to run a delivery attempt on each message in turn,
+but unlike the \-M-\ option, it does check for retry hints, and respects any
+that are found. This option is not very useful to external callers. It is
+provided mainly for internal use by Exim when it needs to re-invoke itself in
+order to regain root privilege for a delivery (see chapter ~~CHAPsecurity).
+However, \-Mc-\ can be useful when testing, in order to run a delivery that
+respects retry times and other options such as \hold@_domains\ that are
+overridden when \-M-\ is used. Such a delivery does not count as a queue run.
+If you want to run a specific delivery as if in a queue run, you should use
+\-q-\ with a message id argument. A distinction between queue run deliveries
+and other deliveries is made in one or two places.
+
+.option Mes #<<message id>>#<<address>>
+.index message||changing sender
+.index sender||changing
+This option requests Exim to change the sender address in the message to the
+given address, which must be a fully qualified address or `<>' (`es' for `edit
+sender'). There must be exactly two arguments. The first argument must be a
+message id, and the second one an email address. However, if the message is
+active (in the middle of a delivery attempt), its status is not altered. This
+option can be used only by an admin user.
+
+.option Mf #<<message id>>#<<message id>> ...
+.index freezing messages
+.index message||manually freezing
+This option requests Exim to mark each listed message as `frozen'. This
+prevents any delivery attempts taking place until the message is `thawed',
+either manually or as a result of the \auto@_thaw\ configuration option.
+However, if any of the messages are active (in the middle of a delivery
+attempt), their status is not altered. This option can be used only by an admin
+user.
+
+.option Mg #<<message id>>#<<message id>> ...
+.index giving up on messages
+.index message||abandoning delivery attempts
+.index delivery||abandoning further attempts
+This option requests Exim to give up trying to deliver the listed messages,
+including any that are frozen. However, if any of the messages are active,
+their status is not altered.
+For non-bounce messages, a delivery error message is sent to the sender,
+containing the text `cancelled by administrator'. Bounce messages are just
+discarded.
+This option can be used only by an admin user.
+
+.option Mmad #<<message id>>#<<message id>> ...
+.index delivery||cancelling all
+This option requests Exim to mark all the recipient addresses in the messages
+as already delivered (`mad' for `mark all delivered'). However, if any message
+is active (in the middle of a delivery attempt), its status is not altered.
+This option can be used only by an admin user.
+
+.option Mmd #<<message id>>#<<address>>#<<address>> ...
+.index delivery||cancelling by address
+.index recipient||removing
+.index removing recipients
+This option requests Exim to mark the given addresses as already delivered
+(`md' for `mark delivered'). The first argument must be a message id, and the
+remaining ones must be email addresses. These are matched to recipient
+addresses in the message in a case-sensitive manner. If the message is active
+(in the middle of a delivery attempt), its status is not altered. This option
+can be used only by an admin user.
+
+.option Mrm #<<message id>>#<<message id>> ...
+.index removing messages
+.index abandoning mail
+.index message||manually discarding
+This option requests Exim to remove the given messages from the queue. No
+bounce messages are sent; each message is simply forgotten. However, if any of
+the messages are active, their status is not altered. This option can be used
+only by an admin user or by the user who originally caused the message to be
+placed on the queue.
+
+.option Mt #<<message id>>#<<message id>> ...
+.index thawing messages
+.index unfreezing messages
+.index frozen messages||thawing
+.index message||thawing frozen
+This option requests Exim to `thaw' any of the listed messages that are
+`frozen', so that delivery attempts can resume. However, if any of the messages
+are active, their status is not altered. This option can be used only by an
+admin user.
+
+.option Mvb #<<message id>>
+.index listing||message body
+.index message||listing body of
+This option causes the contents of the message body (-D) spool file to be
+written to the standard output. This option can be used only by an admin user.
+
+.option Mvh #<<message id>>
+.index listing||message headers
+.index header lines||listing
+.index message||listing header lines
+This option causes the contents of the message headers (-H) spool file to be
+written to the standard output. This option can be used only by an admin user.
+
+.option Mvl #<<message id>>
+.index listing||message log
+.index message||listing message log
+This option causes the contents of the message log spool file to be written to
+the standard output. This option can be used only by an admin user.
+
+.option m
+This is apparently a synonym for \-om-\ that is accepted by Sendmail, so Exim
+treats it that way too.
+
+.option N
+.index debugging||\-N-\ option
+.index debugging||suppressing delivery
+This is a debugging option that inhibits delivery of a message at the transport
+level. It implies \-v-\. Exim goes through many of the motions of delivery --
+it just doesn't actually transport the message, but instead behaves as if it
+had successfully done so. However, it does not make any updates to the retry
+database, and the log entries for deliveries are flagged with `$*$>' rather
+than `=>'.
+
+Because \-N-\ discards any message to which it applies, only root or the Exim
+user are allowed to use it with \-bd-\, \-q-\, \-R-\ or \-M-\. In other words,
+an ordinary user can use it only when supplying an incoming message to which it
+will apply. Although transportation never fails when \-N-\ is set, an address
+may be deferred because of a configuration problem on a transport, or a routing
+problem. Once \-N-\ has been used for a delivery attempt, it sticks to the
+message, and applies to any subsequent delivery attempts that may happen for
+that message.
+
+.option n
+.index Sendmail compatibility||\-n-\ option ignored
+This option is interpreted by Sendmail to mean `no aliasing'. It is ignored by
+Exim.
+
+.option O #<<data>>
+This option is interpreted by Sendmail to mean `set option`. It is ignored by
+Exim.
+
+.option oA #<<file name>>
+.index Sendmail compatibility||\-oA-\ option
+This option is used by Sendmail in conjunction with \-bi-\ to specify an
+alternative alias file name. Exim handles \-bi-\ differently; see the
+description above.
+
+.index SMTP||passed connection
+.option oB #<<n>>
+.index SMTP||multiple deliveries
+.index multiple SMTP deliveries
+This is a debugging option which limits the maximum number of messages that can
+be delivered down one SMTP connection, overriding the value set in any \%smtp%\
+transport. If <<n>> is omitted, the limit is set to 1.
+
+.option odb
+.index background delivery
+.index delivery||in the background
+This option applies to all modes in which Exim accepts incoming messages,
+including the listening daemon. It requests `background' delivery of such
+messages, which means that the accepting process automatically starts delivery
+process for each message received, but does not wait for the delivery process
+to complete. This is the default action if none of the \-od-\ options are
+present.
+
+If one of the queueing options in the configuration file
+(\queue@_only\ or \queue@_only@_file\, for example) is in effect, \-odb-\
+overrides it if \queue@_only@_override\ is set true, which is the default
+setting. If \queue@_only@_override\ is set false, \-odb-\ has no effect.
+
+.option odf
+.index foreground delivery
+.index delivery||in the foreground
+This option requests `foreground' (synchronous) delivery when Exim has accepted
+a locally-generated message. (For the daemon it is exactly the same as
+\-odb-\.) A delivery process is automatically started to deliver the
+message, and Exim waits for it to complete before proceeding.
+However, like \-odb-\, this option has no effect if \queue@_only@_override\ is
+false and one of the queueing options in the configuration file is in effect.
+
+.option odi
+This option is synonymous with \-odf-\. It is provided for compatibility with
+Sendmail.
+
+.option odq
+.index non-immediate delivery
+.index delivery||suppressing immediate
+.index queueing incoming messages
+This option applies to all modes in which Exim accepts incoming messages,
+including the listening daemon. It specifies that the accepting process should
+not automatically start a delivery process for each message received. Messages
+are placed on the queue, and remain there until a subsequent queue runner
+process encounters them.
+There are several configuration options (such as \queue@_only\) that can be
+used to queue incoming messages under certain conditions. This option overrides
+all of them and also \-odqs-\. It always forces queueing.
+
+.option odqs
+.index SMTP||delaying delivery
+This option is a hybrid between \-odb-\/\-odi-\ and \-odq-\.
+However, like \-odb-\ and \-odi-\, this option has no effect if
+\queue@_only@_override\ is false and one of the queueing options in the
+configuration file is in effect.
+
+When \-odqs-\ does operate, a delivery process is started for each incoming
+message, in the background by default, but in the foreground if \-odi-\ is also
+present.
+The recipient addresses are routed, and local deliveries are done in the normal
+way. However, if any SMTP deliveries are required, they are not done at this
+time, so the message remains on the queue until a subsequent queue runner
+process encounters it. Because routing was done, Exim knows which messages are
+waiting for which hosts, and so a number of messages for the same host can be
+sent in a single SMTP connection. The \queue@_smtp@_domains\ configuration
+option has the same effect for specific domains. See also the \-qq-\ option.
+
+.option oee
+.index error||reporting
+If an error is detected while a non-SMTP message is being received (for
+example, a malformed address), the error is reported to the sender in a mail
+message.
+.index return code||for \-oee-\
+Provided this error message is successfully sent, the Exim receiving process
+exits with a return code of zero. If not, the return code is 2 if the problem
+is that the original message has no recipients, or 1 any other error. This is
+the default \-oe$it{x}-\ option if Exim is called as \*rmail*\.
+
+.option oem
+.index error||reporting
+.index return code||for \-oem-\
+This is the same as \-oee-\, except that Exim always exits with a non-zero
+return code, whether or not the error message was successfully sent.
+This is the default \-oe$it{x}-\ option, unless Exim is called as \*rmail*\.
+
+.option oep
+.index error||reporting
+If an error is detected while a non-SMTP message is being received, the
+error is reported by writing a message to the standard error file (stderr).
+.index return code||for \-oep-\
+The return code is 1 for all errors.
+
+.option oeq
+.index error||reporting
+This option is supported for compatibility with Sendmail, but has the same
+effect as \-oep-\.
+
+.option oew
+.index error||reporting
+This option is supported for compatibility with Sendmail, but has the same
+effect as \-oem-\.
+
+.option oi
+.index dot||in incoming, non-SMTP message
+This option, which has the same effect as \-i-\, specifies that a dot on a line
+by itself should not terminate an incoming, non-SMTP message.
+.em
+Otherwise, a single dot does terminate, though Exim does no special processing
+for other lines that start with a dot.
+.nem
+This option is set by default if Exim is called as \*rmail*\. See also \-ti-\.
+
+.option oitrue
+This option is treated as synonymous with \-oi-\.
+
+.option oMa #<<host address>>
+.index sender||host address, specifying for local message
+A number of options starting with \-oM-\ can be used to set values associated
+with remote hosts on locally-submitted messages (that is, messages not received
+over TCP/IP). These options can be used by any caller in conjunction with the
+\-bh-\,
+\-be-\,
+\-bf-\, \-bF-\, \-bt-\, or \-bv-\ testing options. In other circumstances, they
+are ignored unless the caller is trusted.
+
+The \-oMa-\ option sets the sender host address. This may include a port number
+at the end, after a full stop (period). For example:
+.display asis
+exim -bs -oMa 10.9.8.7.1234
+.endd
+An alternative syntax is to enclose the IP address in square brackets, followed
+by a colon and the port number:
+.display asis
+exim -bs -oMa [10.9.8.7]:1234
+.endd
+The IP address is placed in the \$sender@_host@_address$\ variable, and the
+port, if present, in \$sender@_host@_port$\.
+
+.option oMaa #<<name>>
+.index authentication||name, specifying for local message
+See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMaa-\
+option sets the value of \$sender@_host@_authenticated$\ (the authenticator
+name). See chapter ~~CHAPSMTPAUTH for a discussion of SMTP authentication.
+
+.option oMai #<<string>>
+.index authentication||id, specifying for local message
+See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMai-\
+option sets the
+value of \$authenticated@_id$\ (the id that was authenticated).
+This overrides the default value (the caller's login id) for messages from
+local sources. See chapter ~~CHAPSMTPAUTH for a discussion of authenticated
+ids.
+
+.option oMas #<<address>>
+.index authentication||sender, specifying for local message
+See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMas-\
+option sets the authenticated sender value
+in \$authenticated@_sender$\.
+It overrides the sender address that is created from the caller's login id for
+messages from local sources. See chapter ~~CHAPSMTPAUTH for a discussion of
+authenticated senders.
+
+.option oMi #<<interface address>>
+.index interface||address, specifying for local message
+See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMi-\
+option sets the IP interface address value. A port number may be included,
+using the same syntax as for \-oMa-\.
+The interface address is placed in \$interface@_address$\ and the port number,
+if present, in \$interface@_port$\.
+
+.option oMr #<<protocol name>>
+.index protocol||incoming, specifying for local message
+See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMr-\
+option sets the received protocol value
+in \$received@_protocol$\.
+However, this applies only when \-bs-\ is not used. For interactive SMTP input,
+the protocol is determined by whether \\EHLO\\ or \\HELO\\ is used, and is
+always either `local-esmtp' or `local-smtp'. For \-bS-\ (batch SMTP) however,
+the protocol can be set by \-oMr-\.
+
+.option oMs #<<host name>>
+.index sender||host name, specifying for local message
+See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMs-\
+option sets the sender host name
+in \$sender@_host@_name$\. When this option is present, Exim does not attempt
+to look up a host name from an IP address; it uses the name it is given.
+
+.option oMt #<<ident string>>
+.index sender||ident string, specifying for local message
+See \-oMa-\ above for general remarks about the \-oM-\ options. The \-oMt-\
+option sets the sender ident value
+in \$sender@_ident$\.
+The default setting for local callers is the login id of the calling process.
+
+.option om
+.index Sendmail compatibility||\-om-\ option ignored
+In Sendmail, this option means `me too', indicating that the sender of a
+message should receive a copy of the message if the sender appears in an alias
+expansion. Exim always does this, so the option does nothing.
+
+.option oo
+.index Sendmail compatibility||\-oo-\ option ignored
+This option is ignored. In Sendmail it specifies `old style headers', whatever
+that means.
+
+.option oP #<<path>>
+.index pid (process id)||of daemon
+.index daemon||process id (pid)
+This option is useful only in conjunction with \-bd-\ or \-q-\ with a time
+value. The option specifies the file to which the process id of the daemon is
+written. When \-oX-\ is used with \-bd-\, or when \-q-\ with a time is used
+without \-bd-\, this is the only way of causing Exim to write a pid file,
+because in those cases, the normal pid file is not used.
+
+.option or #<<time>>
+.index timeout||for non-SMTP input
+This option sets a timeout value for incoming non-SMTP messages. If it is not
+set, Exim will wait forever for the standard input. The value can also be set
+by the \receive@_timeout\ option. The format used for specifying times is
+described in section ~~SECTtimeformat.
+
+.option os #<<time>>
+.index timeout||for SMTP input
+.index SMTP||timeout, input
+This option sets a timeout value for incoming SMTP messages. The timeout
+applies to each SMTP command and block of data. The value can also be set by
+the \smtp@_receive@_timeout\ option; it defaults to 5 minutes. The format used
+for specifying times is described in section ~~SECTtimeformat.
+
+.option ov
+This option has exactly the same effect as \-v-\.
+
+.option oX #<<number or string>>
+.index TCP/IP||setting listening ports
+.index TCP/IP||setting listening interfaces
+.index port||receiving TCP/IP
+This option is relevant only when the \-bd-\ (start listening daemon) option is
+also given. It controls which ports and interfaces the daemon uses. Details of
+the syntax, and how it interacts with configuration file options, are given in
+chapter ~~CHAPinterfaces. When \-oX-\ is used to start a daemon, no pid file is
+written unless \-oP-\ is also present to specify a pid file name.
+
+.option pd
+.index Perl||starting the interpreter
+This option applies when an embedded Perl interpreter is linked with Exim (see
+chapter ~~CHAPperl). It overrides the setting of the \perl@_at@_start\ option,
+forcing the starting of the interpreter to be delayed until it is needed.
+
+.option ps
+.index Perl||starting the interpreter
+This option applies when an embedded Perl interpreter is linked with Exim (see
+chapter ~~CHAPperl). It overrides the setting of the \perl@_at@_start\ option,
+forcing the starting of the interpreter to occur as soon as Exim is started.
+
+.em
+.option p<<rval>>:<<sval>>
+For compatibility with Sendmail, this option
+is equivalent to
+.display
+-oMr <<rval>> -oMs <<sval>>
+.endd
+It sets the incoming protocol and host name (for trusted callers). The
+host name and its colon can be omitted when only the protocol is to be set.
+Note the Exim already has two private options, \-pd-\ and \-ps-\, that refer to
+embedded Perl. It is therefore impossible to set a protocol value of \"p"\ or
+\"s"\ using this option (but that does not seem a real limitation).
+.nem
+
+.option q
+.index queue runner||starting manually
+This option is normally restricted to admin users. However, there is a
+configuration option called \prod@_requires@_admin\ which can be set false to
+relax this restriction (and also the same requirement for the \-M-\, \-R-\, and
+\-S-\ options).
+
+.index queue runner||description of operation
+The \-q-\ option starts one queue runner process. This scans the queue of
+waiting messages, and runs a delivery process for each one in turn. It waits
+for each delivery process to finish before starting the next one. A delivery
+process may not actually do any deliveries if the retry times for the addresses
+have not been reached. Use \-qf-\ (see below) if you want to override this.
+.index SMTP||passed connection
+.index SMTP||multiple deliveries
+.index multiple SMTP deliveries
+If the delivery process spawns other processes to deliver other messages down
+passed SMTP connections, the queue runner waits for these to finish before
+proceeding.
+
+When all the queued messages have been considered, the original queue runner
+process terminates. In other words, a single pass is made over the waiting
+mail, one message at a time. Use \-q-\ with a time (see below) if you want this
+to be repeated periodically.
+
+Exim processes the waiting messages in an unpredictable order. It isn't very
+random, but it is likely to be different each time, which is all that matters.
+If one particular message screws up a remote MTA, other messages to the same
+MTA have a chance of getting through if they get tried first.
+
+It is possible to cause the messages to be processed in lexical message id
+order, which is essentially the order in which they arrived, by setting the
+\queue@_run@_in@_order\ option, but this is not recommended for normal use.
+
+.option q <<qflags>>
+The \-q-\ option may be followed by one or more flag letters that change its
+behaviour. They are all optional, but if more than one is present, they must
+appear in the correct order. Each flag is described in a separate item below.
+
+.option qq...
+.index queue||double scanning
+.index queue||routing
+.index routing||whole queue before delivery
+An option starting with \-qq-\ requests a two-stage queue run. In the first
+stage, the queue is scanned as if the \queue@_smtp@_domains\ option matched
+every domain. Addresses are routed, local deliveries happen, but no remote
+transports are run.
+.index hints database||remembering routing
+The hints database that remembers which messages are
+waiting for specific hosts is updated, as if delivery to those hosts had been
+deferred. After this is complete, a second, normal queue scan happens, with
+routing and delivery taking place as normal. Messages that are routed to the
+same host should mostly be delivered down a single SMTP
+.index SMTP||passed connection
+.index SMTP||multiple deliveries
+.index multiple SMTP deliveries
+connection because of the hints that were set up during the first queue scan.
+This option may be useful for hosts that are connected to the Internet
+intermittently.
+
+.option q[q]i...
+.index queue||initial delivery
+If the \*i*\ flag is present, the queue runner runs delivery processes only for
+those messages that haven't previously been tried. (\*i*\ stands for `initial
+delivery'.) This can be helpful if you are putting messages on the queue using
+\-odq-\ and want a queue runner just to process the new messages.
+
+.option q[q][i]f...
+.index queue||forcing delivery
+.index delivery||forcing in queue run
+If one \*f*\ flag is present, a delivery attempt is forced for each non-frozen
+message, whereas without \f\ only those non-frozen addresses that have passed
+their retry times are tried.
+
+.option q[q][i]ff...
+.index frozen messages||forcing delivery
+If \*ff*\ is present, a delivery attempt is forced for every message, whether
+frozen or not.
+
+.option q[q][i][f[f]]l
+.index queue||local deliveries only
+The \*l*\ (the letter `ell') flag specifies that only local deliveries are to be
+done. If a message requires any remote deliveries, it remains on the queue for
+later delivery.
+
+.option q <<qflags>>#<<start id>>#<<end id>>
+.index queue||delivering specific messages
+When scanning the queue, Exim can be made to skip over messages whose ids are
+lexically less than a given value by following the \-q-\ option with a starting
+message id. For example:
+.display
+exim -q 0t5C6f-0000c8-00
+.endd
+Messages that arrived earlier than \"0t5C6f-0000c8-00"\ are not inspected. If a
+second message id is given, messages whose ids are lexically greater than it
+are also skipped. If the same id is given twice, for example,
+.display
+exim -q 0t5C6f-0000c8-00 0t5C6f-0000c8-00
+.endd
+just one delivery process is started, for that message. This differs from \-M-\
+in that retry data is respected, and it also differs from \-Mc-\ in that it
+counts as a delivery from a queue run. Note that the selection mechanism does
+not affect the order in which the messages are scanned. There are also other
+ways of selecting specific sets of messages for delivery in a queue run -- see
+\-R-\ and \-S-\.
+
+.option q <<qflags>><<time>>
+.index queue runner||starting periodically
+.index periodic queue running
+When a time value is present, the \-q-\ option causes Exim to run as a daemon,
+starting a queue runner process at intervals specified by the given time value
+(whose format is described in section ~~SECTtimeformat). This form of the \-q-\
+option is commonly combined with the \-bd-\ option, in which case a single
+daemon process handles both functions. A common way of starting up a combined
+daemon at system boot time is to use a command such as
+.display
+/usr/exim/bin/exim -bd -q30m
+.endd
+Such a daemon listens for incoming SMTP calls, and also starts a queue runner
+process every 30 minutes.
+
+When a daemon is started by \-q-\ with a time value, but without \-bd-\, no pid
+file is written unless one is explicitly requested by the \-oP-\ option.
+
+.option qR <<rsflags>>#<<string>>
+This option is synonymous with \-R-\. It is provided for Sendmail
+compatibility.
+
+.option qS <<rsflags>>#<<string>>
+This option is synonymous with \-S-\.
+
+.option R <<rsflags>>#<<string>>
+.index queue runner||for specific recipients
+.index delivery||to given domain
+.index domain||delivery to
+The <<rsflags>> may be empty, in which case the white space before the string
+is optional, unless the string is \*f*\, \*ff*\, \*r*\, \*rf*\, or \*rff*\,
+which are the possible values for <<rsflags>>. White space is required if
+<<rsflags>> is not empty.
+
+This option is similar to \-q-\ with no time value, that is, it causes Exim to
+perform a single queue run, except that, when scanning the messages on the
+queue, Exim processes only those that have at least one undelivered recipient
+address containing the given string, which is checked in a case-independent
+way. If the <<rsflags>> start with \*r*\, <<string>> is interpreted as a regular
+expression; otherwise it is a literal string.
+
+Once a message is selected, all its addresses are processed. For the first
+selected message, Exim overrides any retry information and forces a delivery
+attempt for each undelivered address. This means that if delivery of any
+address in the first message is successful, any existing retry information is
+deleted, and so delivery attempts for that address in subsequently selected
+messages (which are processed without forcing) will run. However, if delivery
+of any address does not succeed, the retry information is updated, and in
+subsequently selected messages, the failing address will be skipped.
+
+If the <<rsflags>> contain \*f*\ or \*ff*\, the delivery forcing applies to all
+selected messages, not just the first;
+.index frozen messages||forcing delivery
+frozen messages are included when \*ff*\ is present.
+
+The \-R-\ option makes it straightforward to initiate delivery of all messages
+to a given domain after a host has been down for some time. When the SMTP
+command \\ETRN\\ is accepted by its ACL (see chapter ~~CHAPACL), its default
+effect is to run Exim with the \-R-\ option, but it can be configured to run an
+arbitrary command instead.
+
+.option r
+This is a documented (for Sendmail) obsolete alternative name for \-f-\.
+
+.index delivery||from given sender
+.option S <<rsflags>>#<<string>>
+.index queue runner||for specific senders
+This option acts like \-R-\ except that it checks the string against each
+message's sender instead of against the recipients. If \-R-\ is also set, both
+conditions must be met for a message to be selected. If either of the options
+has \*f*\ or \*ff*\ in its flags, the associated action is taken.
+
+.em
+.option Tqt#<<times>>
+This an option that is exclusively for use by the Exim testing suite.
+It is not recognized when Exim is run normally. It allows for the setting up
+of explicit `queue times' so that various warning/retry features can be
+tested.
+.nem
+
+.option t
+.index recipient||extracting from header lines
+.index ::Bcc:: header line
+.index ::Cc:: header line
+.index ::To:: header line
+When Exim is receiving a locally-generated, non-SMTP message on its standard
+input, the \-t-\ option causes the recipients of the message to be obtained
+from the ::To::, ::Cc::, and ::Bcc:: header lines in the message instead of from
+the command arguments. The addresses are extracted before any rewriting takes
+place.
+
+.index Sendmail compatibility||\-t-\ option
+If the command has any arguments, they specify addresses to which the message
+is $it{not} to be delivered. That is, the argument addresses are removed from
+the recipients list obtained from the headers. This is compatible with Smail 3
+and in accordance with the documented behaviour of several versions of
+Sendmail, as described in man pages on a number of operating systems (e.g.
+Solaris 8, IRIX 6.5, HP-UX 11). However, some versions of Sendmail $it{add}
+argument addresses to those obtained from the headers, and the O'Reilly
+Sendmail book documents it that way. Exim can be made to add argument addresses
+instead of subtracting them by setting the option
+\extract__addresses__remove__arguments\ false.
+
+If a ::Bcc:: header line is present, it is removed from the message unless
+there is no ::To:: or ::Cc::, in which case a ::Bcc:: line with no data is
+created. This is necessary for conformity with the original RFC 822 standard;
+the requirement has been removed in RFC 2822, but that is still very new.
+
+.index \Resent@-\ header lines||with \-t-\
+If there are any \Resent@-\ header lines in the message, Exim extracts
+recipients from all ::Resent-To::, ::Resent-Cc::, and ::Resent-Bcc:: header
+lines instead of from ::To::, ::Cc::, and ::Bcc::. This is for compatibility
+with Sendmail and other MTAs. (Prior to release 4.20, Exim gave an error if
+\-t-\ was used in conjunction with \Resent@-\ header lines.)
+
+RFC 2822 talks about different sets of \Resent@-\ header lines (for when a
+message is resent several times). The RFC also specifies that they should be
+added at the front of the message, and separated by ::Received:: lines. It is
+not at all clear how \-t-\ should operate in the present of multiple sets,
+nor indeed exactly what constitutes a `set'.
+In practice, it seems that MUAs do not follow the RFC. The \Resent@-\ lines are
+often added at the end of the header, and if a message is resent more than
+once, it is common for the original set of \Resent@-\ headers to be renamed as
+\X-Resent@-\ when a new set is added. This removes any possible ambiguity.
+
+.option ti
+This option is exactly equivalent to \-t-\ \-i-\. It is provided for
+compatibility with Sendmail.
+
+.option tls-on-connect
+.index TLS||use without STARTTLS
+.index TLS||automatic start
+This option is available when Exim is compiled with TLS support. It makes it
+possible to support legacy clients that do not support the \\STARTTLS\\
+command, but instead expect to start up a TLS session as soon as a connection
+to the server is established. These clients use a special port (usually called
+the `ssmtp' port) instead of the normal SMTP port 25. The \-tls-on-connect-\
+option can be used to run Exim in this way from \*inetd*\, and it can also be
+used to run a special daemon that operates in this manner (use \-oX-\ to
+specify the port). However, although it is possible to run one daemon that
+listens on several ports, it is not possible to have some of them operate one
+way and some the other. With only a few clients that need the legacy support, a
+convenient approach is to use a daemon for normal SMTP (with or without
+\\STARTTLS\\) and \*inetd*\ with \-tls-on-connect-\ for the legacy clients.
+
+.option U
+.index Sendmail compatibility||\-U-\ option ignored
+Sendmail uses this option for `initial message submission', and its
+documentation states that in future releases, it may complain about
+syntactically invalid messages rather than fixing them when this flag is not
+set. Exim ignores this option.
+
+.option v
+This option causes Exim to write information to the standard error stream,
+describing what it is doing. In particular, it shows the log lines for
+receiving and delivering a message, and if an SMTP connection is made, the SMTP
+dialogue is shown. Some of the log lines shown may not actually be written to
+the log if the setting of \log@_selector\ discards them. Any relevant selectors
+are shown with each log line. If none are shown, the logging is unconditional.
+
+.option x
+AIX uses \-x-\ for a private purpose (`mail from a local mail program has
+National Language Support extended characters in the body of the mail item').
+It sets \-x-\ when calling the MTA from its \mail\ command. Exim ignores this
+option.
+
+.endoptions
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The Exim run time configuration file
+.set runningfoot "configuration file"
+.rset CHAPconf ~~chapter
+
+.index run time configuration
+.index configuration file||general description
+.index \\CONFIGURE@_FILE\\
+Exim uses a single run time configuration file that is read whenever an Exim
+binary is executed. Note that in normal operation, this happens frequently,
+because Exim is designed to operate in a distributed manner, without central
+control.
+
+The name of the configuration file is compiled into the binary for security
+reasons, and is specified by the \\CONFIGURE@_FILE\\ compilation option. In
+most configurations, this specifies a single file. However, it is permitted to
+give a colon-separated list of file names, in which case Exim uses the first
+existing file in the list.
+
+.index \\EXIM@_USER\\
+.index \\EXIM@_GROUP\\
+.index configuration file||ownership
+.index ownership||configuration file
+The run time configuration file must be owned by root or by the user that
+is specified at compile time by the \\EXIM@_USER\\ option,
+.em
+or by the user that is specified at compile time by the \\CONFIGURE@_OWNER\\
+option (if set).
+.nem
+The configuration file must not be world-writeable or group-writeable, unless
+its group is the one specified at compile time by the \\EXIM@_GROUP\\ option.
+
+\**Warning**\: In a conventional configuration, where the Exim binary is setuid
+to root, anybody who is able to edit the run time configuration file has an
+easy way to run commands as root. If you make your mail administrators members
+of the Exim group, but do not trust them with root, make sure that the run time
+configuration is not group writeable.
+
+
+A default configuration file, which will work correctly in simple situations,
+is provided in the file \(src/configure.default)\.
+If \\CONFIGURE@_FILE\\ defines just one file name, the installation process
+copies the default configuration to a new file of that name if it did not
+previously exist. If \\CONFIGURE@_FILE\\ is a list, no default is automatically
+installed. Chapter ~~CHAPdefconfil is a `walk-through' discussion of the
+default configuration.
+
+.index configuration file||errors in
+.index error||in configuration file
+.index return code||for bad configuration
+If a syntax error is detected while reading the configuration file, Exim
+writes a message on the standard error, and exits with a non-zero return code.
+The message is also written to the panic log.
+
+
+.section Using a different configuration file
+.index configuration file||alternate
+A one-off alternate configuration can be specified by the \-C-\ command line
+option, which may specify a single file or a list of files. However, when \-C-\
+is used, Exim gives up its root privilege, unless called by root or the Exim
+user (or unless the argument for \-C-\ is identical to the built-in value from
+\\CONFIGURE@_FILE\\). \-C-\ is useful mainly for checking the syntax of
+configuration files before installing them. No owner or group checks are done
+on a configuration file specified by \-C-\.
+
+The privileged use of \-C-\ by the Exim user can be locked out by setting
+\\ALT@_CONFIG@_ROOT@_ONLY\\ in \(Local/Makefile)\ when building Exim. However,
+if you do this, you also lock out the possibility of testing a
+configuration using \-C-\ right through message reception and delivery, even if
+the caller is root. The reception works, but by that time, Exim is running as
+the Exim user, so when it re-execs to regain privilege for the delivery, the
+use of \-C-\ causes privilege to be lost. However, root can test reception and
+delivery using two separate commands (one to put a message on the queue, using
+\-odq-\, and another to do the delivery, using \-M-\).
+
+If \\ALT@_CONFIG@_PREFIX\\ is defined \(in Local/Makefile)\, it specifies a
+prefix string with which any file named in a \-C-\ command line option must
+start. In addition, the file name must not contain the sequence \"/../"\. There
+is no default setting for \\ALT@_CONFIG@_PREFIX\\; when it is unset, any file
+name can be used with \-C-\.
+
+One-off changes to a configuration can be specified by the \-D-\ command line
+option, which defines and overrides values for macros used inside the
+configuration file. However, like \-C-\, the use of this option by a
+non-privileged user causes Exim to discard its root privilege.
+If \\DISABLE@_D@_OPTION\\ is defined in \(Local/Makefile)\, the use of \-D-\ is
+completely disabled, and its use causes an immediate error exit.
+
+Some sites may wish to use the same Exim binary on different machines that
+share a file system, but to use different configuration files on each machine.
+If \\CONFIGURE@_FILE@_USE@_NODE\\ is defined in \(Local/Makefile)\, Exim first
+looks for a file whose name is the configuration file name followed by a dot
+and the machine's node name, as obtained from the \*uname()*\ function. If this
+file does not exist, the standard name is tried. This processing occurs for
+each file name in the list given by \\CONFIGURE@_FILE\\ or \-C-\.
+
+In some esoteric situations different versions of Exim may be run under
+different effective uids and the \\CONFIGURE@_FILE@_USE@_EUID\\ is defined to
+help with this. See the comments in \(src/EDITME)\ for details.
+
+
+.section Configuration file format
+.rset SECTconffilfor "~~chapter.~~section"
+.index configuration file||format of
+.index format||configuration file
+Exim's configuration file is divided into a number of different parts. General
+option settings must always appear at the start of the file. The other parts
+are all optional, and may appear in any order. Each part other than the first
+is introduced by the word `begin' followed by the name of the part. The
+optional parts are:
+
+.numberpars $.
+\*ACL*\: Access control lists for controlling incoming SMTP mail.
+.nextp
+.index \\AUTH\\||configuration
+\*authenticators*\: Configuration settings for the authenticator drivers. These
+are concerned with the SMTP \\AUTH\\ command (see chapter ~~CHAPSMTPAUTH).
+.nextp
+\*routers*\: Configuration settings for the router drivers. Routers process
+addresses and determine how the message is to be delivered.
+.nextp
+\*transports*\: Configuration settings for the transport drivers. Transports
+define mechanisms for copying messages to destinations.
+.nextp
+\*retry*\: Retry rules, for use when a message cannot be immediately delivered.
+.nextp
+\*rewrite*\: Global address rewriting rules, for use when a message arrives and
+when new addresses are generated during delivery.
+.nextp
+\*local@_scan*\: Private options for the \*local@_scan()*\ function. If you
+want to use this feature, you must set
+.display asis
+LOCAL_SCAN_HAS_OPTIONS=yes
+.endd
+in \(Local/Makefile)\ before building Exim. Full details of the
+\*local@_scan()*\ facility are given in chapter ~~CHAPlocalscan.
+.endp
+Blank lines in the file, and lines starting with a @# character (ignoring
+leading white space) are treated as comments and are ignored. \**Note**\: a
+@# character other than at the beginning of a line is not treated specially,
+and does not introduce a comment.
+
+Any non-comment line can be continued by ending it with a backslash. Trailing
+white space after the backslash is ignored, and leading white space at the
+start of continuation lines is also ignored.
+Comment lines beginning with @# (but not empty lines) may appear in the middle
+of a sequence of continuation lines.
+
+A convenient way to create a configuration file is to start from the
+default, which is supplied in \(src/configure.default)\, and add, delete, or
+change settings as required.
+
+The ACLs, retry rules, and rewriting rules have their own syntax which is
+described in chapters ~~CHAPACL, ~~CHAPretry, and ~~CHAPrewrite, respectively.
+The other parts of the configuration file have some syntactic items in common,
+and these are described below, from section ~~SECTcos onwards. Before that, the
+inclusion, macro, and conditional facilities are described.
+
+
+.section File inclusions in the configuration file
+.index inclusions in configuration file
+.index configuration file||including other files
+.index .include in configuration file
+.index .include@_if@_exists in configuration file
+You can include other files inside Exim's run time configuration file by
+using this syntax:
+.display
+@.include <<file name>>
+.endd
+or
+.display
+@.include@_if@_exists <<file name>>
+.endd
+on a line by itself. Double quotes round the file name are optional. If you use
+the first form, a configuration error occurs if the file does not exist; the
+second form does nothing for non-existent files.
+
+Includes may be nested to any depth, but remember that Exim reads its
+configuration file often, so it is a good idea to keep them to a minimum.
+If you change the contents of an included file, you must HUP the daemon,
+because an included file is read only when the configuration itself is read.
+
+The processing of inclusions happens early, at a physical line level, so, like
+comment lines, an inclusion can be used in the middle of an option setting,
+for example:
+.display asis
+hosts_lookup = a.b.c \
+ .include /some/file
+.endd
+Include processing happens
+after
+macro processing (see below). Its effect is to process the lines of the file as
+if they occurred inline where the inclusion appears.
+
+
+.section Macros in the configuration file
+.rset SECTmacrodefs "~~chapter.~~section"
+.index macro||description of
+.index configuration file||macros
+If a line in the main part of the configuration (that is, before the first
+`begin' line) begins with an upper case letter, it is taken as a macro
+definition, and must be of the form
+.display
+<<name>> = <<rest of line>>
+.endd
+The name must consist of letters, digits, and underscores, and need not all be
+in upper case, though that is recommended. The rest of the line, including any
+continuations, is the replacement text, and has leading and trailing white
+space removed. Quotes are not removed. The replacement text can never end with
+a backslash character, but this doesn't seem to be a serious limitation.
+
+Once a macro is defined, all subsequent lines in the file (and any included
+files) are scanned for the macro name; if there are several macros, the line is
+scanned for each in turn, in the order in which they are defined. The
+replacement text is not re-scanned for the current macro, though it is scanned
+for subsequently defined macros. For this reason, a macro name may not contain
+the name of a previously defined macro as a substring. You could, for example,
+define
+.display asis
+ABCD_XYZ = <<something>>
+ABCD = <<something else>>
+.endd
+but putting the definitions in the opposite order would provoke a configuration
+error.
+
+Macro expansion is applied to individual lines from the file, before checking
+for line continuation or file inclusion (see below). If a line consists solely
+of a macro name, and the expansion of the macro is empty, the line is ignored.
+A macro at the start of a line may turn the line into a comment line or a
+\".include"\ line.
+
+As an example of macro usage, consider a configuration where aliases are looked
+up in a MySQL database. It helps to keep the file less cluttered if long
+strings such as SQL statements are defined separately as macros, for example:
+.display asis
+ALIAS_QUERY = select mailbox from user where \
+ login=${quote_mysql:$local_part};
+.endd
+This can then be used in a \%redirect%\ router setting like this:
+.display asis
+data = ${lookup mysql{ALIAS_QUERY}}
+.endd
+In earlier versions of Exim macros were sometimes used for domain, host, or
+address lists. In Exim 4 these are handled better by named lists -- see section
+~~SECTnamedlists.
+
+Macros in the configuration file can be overridden by the \-D-\ command line
+option, but Exim gives up its root privilege when \-D-\ is used, unless called
+by root or the Exim user.
+
+
+.section Conditional skips in the configuration file
+.index configuration file||conditional skips
+.index .ifdef
+You can use the directives \".ifdef"\, \".ifndef"\, \".elifdef"\,
+\".elifndef"\, \".else"\, and \".endif"\ to dynamically include or exclude
+portions of the configuration file. The processing happens whenever the file is
+read (that is, when an Exim binary starts to run).
+
+The implementation is very simple. Instances of the first four directives must
+be followed by text that includes the names of one or macros. The condition
+that is tested is whether or not any macro substitution has taken place in the
+line. Thus:
+.display
+@.ifdef AAA
+message@_size@_limit = 50M
+@.else
+message@_size@_limit = 100M
+@.endif
+.endd
+sets a message size limit of 50M if the macro \"AAA"\ is defined, and 100M
+otherwise. If there is more than one macro named on the line, the condition
+is true if any of them are defined. That is, it is an `or' condition. To
+obtain an `and' condition, you need to use nested \".ifdef"\s.
+
+Although you can use a macro expansion to generate one of these directives,
+it is not very useful, because the condition `there was a macro substitution
+in this line' will always be true.
+
+Text following \".else"\ and \".endif"\ is ignored, and can be used as comment
+to clarify complicated nestings.
+
+
+.section Common option syntax
+.rset SECTcos "~~chapter.~~section"
+.index common option syntax
+.index syntax of common options
+.index configuration file||common option syntax
+For the main set of options, driver options, and \*local@_scan()*\ options,
+each setting is on a line by itself, and starts with a name consisting of
+lower-case letters and underscores. Many options require a data value, and in
+these cases the name must be followed by an equals sign (with optional white
+space) and then the value. For example:
+.display asis
+qualify_domain = mydomain.example.com
+.endd
+Some option settings may contain sensitive data, for example, passwords for
+accessing databases. To stop non-admin users from using the \-bP-\ command line
+option to read these values, you can precede the option settings with the word
+`hide'. For example:
+.display asis
+hide mysql_servers = localhost/users/admin/secret-password
+.endd
+For non-admin users, such options are displayed like this:
+.display asis
+mysql_servers = <value not displayable>
+.endd
+If `hide' is used on a driver option, it hides the value of that option on all
+instances of the same driver.
+
+The following sections describe the syntax used for the different data types
+that are found in option settings.
+
+.section Boolean options
+.index format||boolean
+.index boolean configuration values
+Options whose type is given as boolean are on/off switches. There are two
+different ways of specifying such options: with and without a data value. If
+the option name is specified on its own without data, the switch is turned on;
+if it is preceded by `no@_' or `not@_' the switch is turned off. However,
+boolean options may optionally be followed by an equals sign and one of the
+words `true', `false', `yes', or `no', as an alternative syntax. For example,
+the following two settings have exactly the same effect:
+.display asis
+queue_only
+queue_only = true
+.endd
+The following two lines also have the same (opposite) effect:
+.display asis
+no_queue_only
+queue_only = false
+.endd
+You can use whichever syntax you prefer.
+
+
+
+.section Integer values
+.index integer configuration values
+.index format||integer
+If an integer data item starts with the characters `0x', the remainder of it
+is interpreted as a hexadecimal number. Otherwise, it is treated as octal if it
+starts with the digit 0, and decimal if not. If an integer value is followed by
+the letter K, it is multiplied by 1024; if it is followed by the letter M, it
+is multiplied by 1024x1024.
+
+When the values of integer option settings are output, values which are an
+exact multiple of 1024 or 1024x1024 are
+sometimes, but not always,
+printed using the letters K and M. The printing style is independent of the
+actual input format that was used.
+
+.section Octal integer values
+.index integer format
+.index format||octal integer
+The value of an option specified as an octal integer is always interpreted in
+octal, whether or not it starts with the digit zero. Such options are always
+output in octal.
+
+
+.section Fixed point number values
+.index fixed point configuration values
+.index format||fixed point
+A fixed point number consists of a decimal integer, optionally followed by a
+decimal point and up to three further digits.
+
+
+.section Time interval values
+.index time interval||specifying in configuration
+.index format||time interval
+.rset SECTtimeformat "~~chapter.~~section"
+A time interval is specified as a sequence of numbers, each followed by one of
+the following letters, with no intervening white space:
+.display rm
+.tabs 5
+\s\ $t seconds
+\m\ $t minutes
+\h\ $t hours
+\d\ $t days
+\w\ $t weeks
+.endd
+For example, `3h50m' specifies 3 hours and 50 minutes. The values of time
+intervals are output in the same format.
+Exim does not restrict the values; it is perfectly acceptable, for example, to
+specify `90m' instead of `1h30m'.
+
+
+.section String values
+.index string||format of configuration values
+.index format||string
+.rset SECTstrings "~~chapter.~~section"
+If a string data item does not start with a double-quote character, it is taken
+as consisting of the remainder of the line plus any continuation lines,
+starting at the first character after any leading white space, with trailing
+white space characters removed, and with no interpretation of the characters in
+the string. Because Exim removes comment lines (those beginning with @#) at an
+early stage, they can appear in the middle of a multi-line string. The
+following settings are therefore equivalent:
+.display asis
+trusted_users = uucp:mail
+
+trusted_users = uucp:\
+ # This comment line is ignored
+ mail
+.endd
+.index string||quoted
+.index escape characters in quoted strings
+If a string does start with a double-quote, it must end with a closing
+double-quote, and any backslash characters other than those used for line
+continuation are interpreted as escape characters, as follows:
+.display
+.tabs 15
+@\@\ $t $rm{single backslash}
+@\n $t $rm{newline}
+@\r $t $rm{carriage return}
+@\t $t $rm{tab}
+@\<<octal digits>> $t $rm{up to 3 octal digits specify one character}
+@\x<<hex digits>> $t $rm{up to 2 hexadecimal digits specify one character}
+.endd
+If a backslash is followed by some other character, including a double-quote
+character, that character replaces the pair.
+
+Quoting is necessary only if you want to make use of the backslash escapes to
+insert special characters, or if you need to specify a value with leading or
+trailing spaces. These cases are rare, so quoting is almost never needed in
+current versions of Exim. In versions of Exim before 3.14, quoting was required
+in order to continue lines, so you may come across older configuration files
+and examples that apparently quote unnecessarily.
+
+.section Expanded strings
+.index string||expansion, definition of
+.index expansion||definition of
+Some strings in the configuration file are subjected to \*string expansion*\,
+by which means various parts of the string may be changed according to the
+circumstances (see chapter ~~CHAPexpand). The input syntax for such strings is
+as just described; in particular, the handling of backslashes in quoted strings
+is done as part of the input process, before expansion takes place. However,
+backslash is also an escape character for the expander, so any backslashes that
+are required for that reason must be doubled if they are within a quoted
+configuration string.
+
+.section User and group names
+.index user name||format of
+.index format||user name
+.index group||name format
+.index format||group name
+User and group names are specified as strings, using the syntax described
+above, but the strings are interpreted specially. A user or group name must
+either consist entirely of digits, or be a name that can be looked up using the
+\*getpwnam()*\ or \*getgrnam()*\ function, as appropriate.
+
+.section List construction
+.index list||syntax of in configuration
+.index format||list item in configuration
+.index string list, definition
+.rset SECTlistconstruct "~~chapter.~~section"
+The data for some configuration options is a colon-separated list of items.
+Many of these options are shown with type `string list' in the descriptions
+later in this document. Others are listed as `domain list', `host list',
+`address list', or `local part list'. Syntactically, they are all the same;
+however, those other than `string list' are subject to particular kinds of
+interpretation, as described in chapter ~~CHAPdomhosaddlists.
+
+In all these cases, the entire list is treated as a single string as far as the
+input syntax is concerned. The \trusted@_users\ setting in section
+~~SECTstrings above is an example. If a colon is actually needed in an item in
+a list, it must be entered as two colons. Leading and trailing white space on
+each item in a list is ignored. This makes it possible to include items that
+start with a colon, and in particular, certain forms of IPv6 address. For
+example, the list
+.display asis
+local_interfaces = 127.0.0.1 : ::::1
+.endd
+contains two IP addresses, the IPv4 address 127.0.0.1 and the IPv6 address
+@:@:1. IPv6 addresses are going to become more and more common as the new
+protocol gets more widely deployed.
+.index list||separator, changing
+.index IPv6||addresses in lists
+Doubling their colons is an unwelcome chore, so a mechanism was introduced to
+allow the separator character to be changed. If a list begins with a left angle
+bracket, followed by any punctuation character, that character is used instead
+of colon as the list separator. For example, the list above can be rewritten to
+use a semicolon separator like this:
+.display asis
+local_interfaces = <; 127.0.0.1 ; ::1
+.endd
+This facility applies to all lists, with the exception of the list in
+\log@_file@_path\. It is recommended that the use of non-colon separators be
+confined to circumstances where they really are needed.
+
+
+.section Format of driver configurations
+.rset SECTfordricon "~~chapter.~~section"
+.index drivers||configuration format
+There are separate parts in the configuration for defining routers, transports,
+and authenticators. In each part, you are defining a number of driver
+instances, each with its own set of options. Each driver instance is defined by
+a sequence of lines like this:
+.display
+<<instance name>>:
+ <<option>>
+ ...
+ <<option>>
+.endd
+In the following example, the instance name is \%localuser%\, and it is
+followed by three options settings:
+.display asis
+localuser:
+ driver = accept
+ check_local_user
+ transport = local_delivery
+.endd
+For each driver instance, you specify which Exim code module it uses -- by the
+setting of the \driver\ option -- and (optionally) some configuration settings.
+For example, in the case of transports, if you want a transport to deliver with
+SMTP you would use the \%smtp%\ driver; if you want to deliver to a local file
+you would use the \%appendfile%\ driver. Each of the drivers is described in
+detail in its own separate chapter later in this manual.
+
+You can have several routers, transports, or authenticators that are based on
+the same underlying driver (each must have a different name).
+
+The order in which routers are defined is important, because addresses are
+passed to individual routers one by one, in order. The order in which
+transports are defined does not matter at all. The order in which
+authenticators are defined is used only when Exim, as a client, is searching
+them to find one that matches an authentication mechanism offered by the
+server.
+
+.index generic options
+.index options||generic, definition of
+Within a driver instance definition, there are two kinds of option:
+$it{generic} and $it{private}. The generic options are those that apply to all
+drivers of the same type (that is, all routers, all transports or all
+authenticators).
+The \driver\ option is a generic option that must appear in every definition.
+.index private options
+The private options are special for each driver, and none need appear, because
+they all have default values.
+
+The options may appear in any order, except that the \driver\ option must
+precede any private options, since these depend on the particular driver. For
+this reason, it is recommended that \driver\ always be the first option.
+
+Driver instance names, which are used for reference in log entries and
+elsewhere, can be any sequence of letters, digits, and underscores (starting
+with a letter) and must be unique among drivers of the same type. A router and
+a transport (for example) can each have the same name, but no two router
+instances can have the same name. The name of a driver instance should not be
+confused with the name of the underlying driver module. For example, the
+configuration lines:
+.display asis
+remote_smtp:
+ driver = smtp
+.endd
+create an instance of the \%smtp%\ transport driver whose name is
+\%remote@_smtp%\. The same driver code can be used more than once, with
+different instance names and different option settings each time. A second
+instance of the \%smtp%\ transport, with different options, might be defined
+thus:
+.display asis
+special_smtp:
+ driver = smtp
+ port = 1234
+ command_timeout = 10s
+.endd
+The names \%remote@_smtp%\ and \%special@_smtp%\ would be used to reference
+these transport instances from routers, and these names would appear in log
+lines.
+
+Comment lines may be present in the middle of driver specifications. The full
+list of option settings for any particular driver instance, including all the
+defaulted values, can be extracted by making use of the \-bP-\ command line
+option.
+
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The default configuration file
+.set runningfoot "default configuration"
+.rset CHAPdefconfil "~~chapter"
+.index configuration file||default, `walk through'
+.index default||configuration file `walk through'
+The default configuration file supplied with Exim as \(src/configure.default)\
+is sufficient for a host with simple mail requirements. As an introduction to
+the way Exim is configured, this chapter `walks through' the default
+configuration, giving brief explanations of the settings. Detailed descriptions
+of the options are given in subsequent chapters. The default configuration file
+itself contains extensive comments about ways you might want to modify the
+initial settings. However, note that there are many options that are not
+mentioned at all in the default configuration.
+
+
+.section Main configuration settings
+The main (global) configuration option settings must always come first in the
+file. The first thing you'll see in the file, after some initial comments, is
+the line
+.display asis
+# primary_hostname =
+.endd
+This is a commented-out setting of the \primary@_hostname\ option. Exim needs
+to know the official, fully qualified name of your host, and this is where you
+can specify it. However, in most cases you do not need to set this option. When
+it is unset, Exim uses the \*uname()*\ system function to obtain the host name.
+
+The first three non-comment configuration lines are as follows:
+.display asis
+domainlist local_domains = @
+domainlist relay_to_domains =
+hostlist relay_from_hosts = 127.0.0.1
+.endd
+These are not, in fact, option settings. They are definitions of two named
+domain lists and one named host list. Exim allows you to give names to lists of
+domains, hosts, and email addresses, in order to make it easier to manage the
+configuration file (see section ~~SECTnamedlists).
+
+The first line defines a domain list called \*local@_domains*\; this is used
+later in the configuration to identify domains that are to be delivered
+on the local host.
+.index @@ in a domain list
+There is just one item in this list, the string `@@'. This is a special form of
+entry which means `the name of the local host'. Thus, if the local host is
+called \*a.host.example*\, mail to \*any.user@@a.host.example*\ is expected to
+be delivered locally. Because the local host's name is referenced indirectly,
+the same configuration file can be used on different hosts.
+
+The second line defines a domain list called \*relay@_to@_domains*\, but the
+list itself is empty. Later in the configuration we will come to the part that
+controls mail relaying through the local host; it allows relaying to any
+domains in this list. By default, therefore, no relaying on the basis of a mail
+domain is permitted.
+
+The third line defines a host list called \*relay@_from@_hosts*\. This list is
+used later in the configuration to permit relaying from any host or IP address
+that matches the list. The default contains just the IP address of the IPv4
+loopback interface, which means that processes on the local host are able to
+submit mail for relaying by sending it over TCP/IP to that interface. No other
+hosts are permitted to submit messages for relaying.
+
+Just to be sure there's no misunderstanding: at this point in the configuration
+we aren't actually setting up any controls. We are just defining some domains
+and hosts that will be used in the controls that are specified later.
+
+The next configuration line is a genuine option setting:
+.display asis
+acl_smtp_rcpt = acl_check_rcpt
+.endd
+This option specifies an \*Access Control List*\ (ACL) which is to be used
+during an incoming SMTP session for every recipient of a message (every
+\\RCPT\\ command). The name of the list is \*acl@_check@_rcpt*\, and we will
+come to its definition below, in the ACL section of the configuration. ACLs
+control which recipients are accepted for an incoming message -- if a
+configuration does not provide an ACL to check recipients, no SMTP mail can be
+accepted.
+
+Two commented-out options settings are next:
+.display asis
+# qualify_domain =
+# qualify_recipient =
+.endd
+The first of these specifies a domain that Exim uses when it constructs a
+complete email address from a local login name. This is often needed when Exim
+receives a message from a local process. If you do not set \qualify@_domain\,
+the value of \primary@_hostname\ is used. If you set both of these options, you
+can have different qualification domains for sender and recipient addresses. If
+you set only the first one, its value is used in both cases.
+
+.index domain literal||recognizing format
+The following line must be uncommented if you want Exim to recognize
+addresses of the form \*user@@[10.11.12.13]*\ that is, with a `domain literal'
+(an IP address) instead of a named domain.
+.display asis
+# allow_domain_literals
+.endd
+.em
+The RFCs still require this form, but many people think that in the modern
+Internet it makes little sense to permit mail to be sent to specific hosts by
+quoting their IP addresses. This ancient format has been used by people who
+try to abuse hosts by using them for unwanted relaying. However, some
+people believe there are circumstances (for example, messages addressed to
+\*postmaster*\) where domain literals are still useful.
+.nem
+
+The next configuration line is a kind of trigger guard:
+.display asis
+never_users = root
+.endd
+It specifies that no delivery must ever be run as the root user. The normal
+convention is to set up \*root*\ as an alias for the system administrator. This
+setting is a guard against slips in the configuration.
+The list of users specified by \never@_users\ is not, however, the complete
+list; the build-time configuration in \(Local/Makefile)\ has an option called
+\\FIXED@_NEVER@_USERS\\ specifying a list that cannot be overridden. The
+contents of \never@_users\ are added to this list. By default
+\\FIXED@_NEVER@_USERS\\ also specifies root.
+
+When a remote host connects to Exim in order to send mail, the only information
+Exim has about the host's identity is its IP address. The next configuration
+line,
+.display asis
+host_lookup = *
+.endd
+specifies that Exim should do a reverse DNS lookup on all incoming connections,
+in order to get a host name. This improves the quality of the logging
+information, but if you feel it is too expensive, you can remove it entirely,
+or restrict the lookup to hosts on `nearby' networks.
+Note that it is not always possible to find a host name from an IP address,
+because not all DNS reverse zones are maintained, and sometimes DNS servers are
+unreachable.
+
+The next two lines are concerned with \*ident*\ callbacks, as defined by RFC
+1413 (hence their names):
+.display asis
+rfc1413_hosts = *
+rfc1413_query_timeout = 30s
+.endd
+These settings cause Exim to make ident callbacks for all incoming SMTP calls.
+You can limit the hosts to which these calls are made, or change the timeout
+that is used. If you set the timeout to zero, all ident calls are disabled.
+Although they are cheap and can provide useful information for tracing problem
+messages, some hosts and firewalls have problems with ident calls. This can
+result in a timeout instead of an immediate refused connection, leading to
+delays on starting up an incoming SMTP session.
+
+When Exim receives messages over SMTP connections, it expects all addresses to
+be fully qualified with a domain, as required by the SMTP definition. However,
+if you are running a server to which simple clients submit messages, you may
+find that they send unqualified addresses. The two commented-out options:
+.display asis
+# sender_unqualified_hosts =
+# recipient_unqualified_hosts =
+.endd
+show how you can specify hosts that are permitted to send unqualified sender
+and recipient addresses, respectively.
+
+The \percent@_hack@_domains\ option is also commented out:
+.display asis
+# percent_hack_domains =
+.endd
+It provides a list of domains for which the `percent hack' is to operate. This
+is an almost obsolete form of explicit email routing. If you do not know
+anything about it, you can safely ignore this topic.
+
+The last two settings in the main part of the default configuration are
+concerned with messages that have been `frozen' on Exim's queue. When a message
+is frozen, Exim no longer continues to try to deliver it. Freezing occurs when
+a bounce message encounters a permanent failure because the sender address of
+the original message that caused the bounce is invalid, so the bounce cannot be
+delivered. This is probably the most common case, but there are also other
+conditions that cause freezing, and frozen messages are not always bounce
+messages.
+.display asis
+ignore_bounce_errors_after = 2d
+timeout_frozen_after = 7d
+.endd
+The first of these options specifies that failing bounce messages are to be
+discarded after 2 days on the queue. The second specifies that any frozen
+message (whether a bounce message or not) is to be timed out (and discarded)
+after a week. In this configuration, the first setting ensures that no failing
+bounce message ever lasts a week.
+
+
+.section ACL configuration
+.index default||ACLs
+.index ~~ACL||default configuration
+In the default configuration, the ACL section follows the main configuration.
+It starts with the line
+.display asis
+begin acl
+.endd
+and it contains the definition of one ACL called \*acl@_check@_rcpt*\ that was
+referenced in the setting of \acl@_smtp@_rcpt\ above.
+.index \\RCPT\\||ACL for
+This ACL is used for every \\RCPT\\ command in an incoming SMTP message. Each
+\\RCPT\\ command specifies one of the message's recipients. The ACL statements
+are considered in order, until the recipient address is either accepted or
+rejected. The \\RCPT\\ command is then accepted or rejected, according to the
+result of the ACL processing.
+.display asis
+acl_check_rcpt:
+.endd
+This line, consisting of a name terminated by a colon, marks the start of the
+ACL, and names it.
+.display asis
+accept hosts = :
+.endd
+This ACL statement accepts the recipient if the sending host matches the list.
+But what does that strange list mean? It doesn't actually contain any host
+names or IP addresses. The presence of the colon puts an empty item in the
+list; Exim matches this only if the incoming message didn't come from a remote
+host. The colon is important. Without it, the list itself is empty, and can
+never match anything.
+
+What this statement is doing is to accept unconditionally all recipients in
+messages that are submitted by SMTP from local processes using the standard
+input and output (that is, not using TCP/IP). A number of MUAs operate in this
+manner.
+.display asis
+deny domains = +local_domains
+ local_parts = ^[.] : ^.*[@%!/|]
+
+deny domains = !+local_domains
+ local_parts = ^[./|] : ^.*[@%!] : ^.*/\\.\\./
+.endd
+These statements are concerned with local parts that contain any of the
+characters `@@', `%', `!', `/', `|', or dots in unusual places. Although these
+characters are entirely legal in local parts (in the case of `@@' and leading
+dots, only if correctly quoted), they do not commonly occur in Internet mail
+addresses.
+
+The first three have in the past been associated with explicitly routed
+addresses (percent is still sometimes used -- see the \percent@_hack@_domains\
+option). Addresses containing these characters are regularly tried by spammers
+in an attempt to bypass relaying restrictions, and also by open relay testing
+programs. Unless you really need them it is safest to reject these characters
+at this early stage. This configuration is heavy-handed in rejecting these
+characters for all messages it accepts from remote hosts. This is a deliberate
+policy of being as safe as possible.
+
+The first rule above is stricter, and is applied to messages that are addressed
+to one of the local domains handled by this host. This is implemented by the
+first condition, which restricts it to domains that are listed in the
+\*local@_domains*\ domain list. The `+' character is used to indicate a
+reference to a named list. In this configuration, there is just one domain in
+\*local@_domains*\, but in general there may be many.
+
+The second condition on the first statement uses two regular expressions to
+block local parts that begin with a dot or contain `@@', `%', `!', `/', or `|'.
+If you have local accounts that include these characters, you will have to
+modify this rule.
+
+Empty components (two dots in a row) are not valid in RFC 2822, but Exim
+allows them because they have been encountered in practice. (Consider local
+parts constructed as `first-initial.second-initial.family-name' when applied to
+someone like the author of Exim, who has no second initial.) However, a local
+part starting with a dot or containing `/../' can cause trouble if it is used
+as part of a file name (for example, for a mailing list). This is also true for
+local parts that contain slashes. A pipe symbol can also be troublesome if the
+local part is incorporated unthinkingly into a shell command line.
+
+The second rule above applies to all other domains, and is less strict. This
+allows your own users to send outgoing messages to sites that use slashes
+and vertical bars in their local parts. It blocks local parts that begin
+with a dot, slash, or vertical bar, but allows these characters within the
+local part. However, the sequence `/../' is barred. The use of `@@', `%', and
+`!' is blocked, as before. The motivation here is to prevent your users (or
+your users' viruses) from mounting certain kinds of attack on remote sites.
+
+.display asis
+accept local_parts = postmaster
+ domains = +local_domains
+.endd
+This statement, which has two conditions, accepts an incoming address if the
+local part is \*postmaster*\ and the domain is one of those listed in the
+\*local@_domains*\ domain list. The `+' character is used to indicate a
+reference to a named list. In this configuration, there is just one domain in
+\*local@_domains*\, but in general there may be many.
+
+The presence of this statement means that mail to postmaster is never blocked
+by any of the subsequent tests. This can be helpful while sorting out problems
+in cases where the subsequent tests are incorrectly denying access.
+.display asis
+require verify = sender
+.endd
+This statement requires the sender address to be verified before any subsequent
+ACL statement can be used. If verification fails, the incoming recipient
+address is refused. Verification consists of trying to route the address, to
+see if a
+bounce
+message could be delivered to it. In the case of remote addresses, basic
+verification checks only the domain, but \*callouts*\ can be used for more
+verification if required. Section ~~SECTaddressverification discusses the
+details of address verification.
+
+.display asis
+# deny message = rejected because $sender_host_address is \
+# in a black list at $dnslist_domain\n\
+# $dnslist_text
+# dnslists = black.list.example
+#
+# warn message = X-Warning: $sender_host_address is \
+# in a black list at $dnslist_domain
+# log_message = found in $dnslist_domain
+# dnslists = black.list.example
+.endd
+These commented-out lines are examples of how you could configure Exim to check
+sending hosts against a DNS black list. The first statement rejects messages
+from blacklisted hosts, whereas the second merely inserts a warning header
+line.
+
+.display asis
+accept domains = +local_domains
+ endpass
+ message = unknown user
+ verify = recipient
+.endd
+This statement accepts the incoming recipient address if its domain is one of
+the local domains, but only if the address can be verified. Verification of
+local addresses normally checks both the local part and the domain. The
+\endpass\ line needs some explanation: if the condition above \endpass\ fails,
+that is, if the address is not in a local domain, control is passed to the next
+ACL statement. However, if the condition below \endpass\ fails, that is, if a
+recipient in a local domain cannot be verified, access is denied and the
+recipient is rejected.
+.index customizing||ACL failure message
+The \message\ modifier provides a customized error message for the failure.
+.display asis
+accept domains = +relay_to_domains
+ endpass
+ message = unrouteable address
+ verify = recipient
+.endd
+This statement accepts the incoming recipient address if its domain is one of
+the domains for which this host is a relay, but again, only if the address can
+be verified.
+.display asis
+accept hosts = +relay_from_hosts
+.endd
+Control reaches this statement only if the recipient's domain is neither a
+local domain, nor a relay domain. The statement accepts the address if the
+message is coming from one of the hosts that are defined as being allowed to
+relay through this host. Recipient verification is omitted here, because in
+many cases the clients are dumb MUAs that do not cope well with SMTP error
+responses. If you are actually relaying out from MTAs, you should probably add
+recipient verification here.
+.display asis
+accept authenticated = *
+.endd
+Control reaches here for attempts to relay to arbitrary domains from arbitrary
+hosts. The statement accepts the address only if the client host has
+authenticated itself. The default configuration does not define any
+authenticators, which means that no client can in fact authenticate. You will
+need to add authenticator definitions if you want to make use of this ACL
+statement.
+.display asis
+deny message = relay not permitted
+.endd
+The final statement denies access, giving a specific error message. Reaching
+the end of the ACL also causes access to be denied, but with the generic
+message `administrative prohibition'.
+
+
+.section Router configuration
+.index default||routers
+.index routers||default
+The router configuration comes next in the default configuration, introduced
+by the line
+.display asis
+begin routers
+.endd
+Routers are the modules in Exim that make decisions about where to send
+messages. An address is passed to each router in turn, until it is either
+accepted, or failed. This means that the order in which you define the routers
+matters. Each router is fully described in its own chapter later in this
+manual. Here we give only brief overviews.
+
+.index domain literal||default router
+.display asis
+# domain_literal:
+# driver = ipliteral
+# domains = !+local_domains
+# transport = remote_smtp
+.endd
+This router is commented out because the majority of sites do not want to
+support domain literal addresses (those of the form \*user@@[10.9.8.7]*\). If
+you uncomment this router, you also need to uncomment the setting of
+\allow@_domain@_literals\ in the main part of the configuration.
+
+.display asis
+dnslookup:
+ driver = dnslookup
+ domains = ! +local_domains
+ transport = remote_smtp
+.newline
+ ignore_target_hosts = 0.0.0.0 : 127.0.0.0/8
+.newline
+ no_more
+.endd
+The first uncommented router handles addresses that do not involve any local
+domains. This is specified by the line
+.display asis
+domains = ! +local_domains
+.endd
+The \domains\ option lists the domains to which this router applies, but the
+exclamation mark is a negation sign, so the router is used only for domains
+that are not in the domain list called \*local@_domains*\ (which was defined at
+the start of the configuration). The plus sign before \*local@_domains*\
+indicates that it is referring to a named list. Addresses in other domains are
+passed on to the following routers.
+
+The name of the router driver is \%dnslookup%\,
+and is specified by the \driver\ option. Do not be confused by the fact that
+the name of this router instance is the same as the name of the driver. The
+instance name is arbitrary, but the name set in the \driver\ option must be one
+of the driver modules that is in the Exim binary.
+
+The \%dnslookup%\ router routes addresses by looking up their domains in the
+DNS in order to obtain a list of hosts to which the address is routed. If the
+router succeeds, the address is queued for the \%remote@_smtp%\ transport, as
+specified by the \transport\ option. If the router does not find the domain in
+the DNS, no further routers are tried because of the \no@_more\ setting, so the
+address fails and is bounced.
+
+The \ignore@_target@_hosts\ option specifies a list of IP addresses that are to
+be entirely ignored. This option is present because a number of cases have been
+encountered where MX records in the DNS point to host names
+whose IP addresses are 0.0.0.0 or are in the 127 subnet (typically 127.0.0.1).
+Completely ignoring these IP addresses causes Exim to fail to route the
+email address, so it bounces. Otherwise, Exim would log a routing problem, and
+continue to try to deliver the message periodically until the address timed
+out.
+.display asis
+system_aliases:
+ driver = redirect
+ allow_fail
+ allow_defer
+ data = ${lookup{$local_part}lsearch{/etc/aliases}}
+# user = exim
+ file_transport = address_file
+ pipe_transport = address_pipe
+.endd
+Control reaches this and subsequent routers only for addresses in the local
+domains. This router checks to see whether the local part is defined as an
+alias in the \(/etc/aliases)\ file, and if so, redirects it according to the
+data that it looks up from that file. If no data is found for the local part,
+the value of the \data\ option is empty, causing the address to be passed to
+the next router.
+
+\(/etc/aliases)\ is a conventional name for the system aliases file that is
+often used. That is why it is referenced by from the default configuration
+file. However, you can change this by setting \\SYSTEM@_ALIASES@_FILE\\ in
+\(Local/Makefile)\ before building Exim.
+
+.display asis
+userforward:
+ driver = redirect
+ check_local_user
+ file = $home/.forward
+ no_verify
+ no_expn
+ check_ancestor
+# allow_filter
+ file_transport = address_file
+ pipe_transport = address_pipe
+ reply_transport = address_reply
+.endd
+This is the most complicated router in the default configuration. It is another
+redirection router, but this time it is looking for forwarding data set up by
+individual users. The \check@_local@_user\ setting means that the first thing it
+does is to check that the local part of the address is the login name of a
+local user. If it is not, the router is skipped. When a local user is found,
+the file called \(.forward)\ in the user's home directory is consulted. If it
+does not exist, or is empty, the router declines. Otherwise, the contents of
+\(.forward)\ are interpreted as redirection data (see chapter ~~CHAPredirect
+for more details).
+
+.index Sieve filter||enabling in default router
+Traditional \(.forward)\ files contain just a list of addresses, pipes, or
+files. Exim supports this by default. However, if \allow@_filter\ is set (it is
+commented out by default), the contents of the file are interpreted as a set of
+Exim or Sieve filtering instructions, provided the file begins with `@#Exim
+filter' or `@#Sieve filter', respectively. User filtering is discussed in the
+separate document entitled \*Exim's interfaces to mail filtering*\.
+
+The \no@_verify\ and \no@_expn\ options mean that this router is skipped when
+verifying addresses, or when running as a consequence of an SMTP \\EXPN\\
+command.
+There are two reasons for doing this:
+.numberpars
+Whether or not a local user has a \(.forward)\ file is not really relevant when
+checking an address for validity; it makes sense not to waste resources doing
+unnecessary work.
+.nextp
+More importantly, when Exim is verifying addresses or handling an \\EXPN\\
+command during an SMTP session, it is running as the Exim user, not as root.
+The group is the Exim group, and no additional groups are set up.
+It may therefore not be possible for Exim to read users' \(.forward)\ files at
+this time.
+.endp
+
+The setting of \check@_ancestor\ prevents the router from generating a new
+address that is the same as any previous address that was redirected. (This
+works round a problem concerning a bad interaction between aliasing and
+forwarding -- see section ~~SECTredlocmai).
+
+The final three option settings specify the transports that are to be used when
+forwarding generates a direct delivery to a file, or to a pipe, or sets up an
+auto-reply, respectively. For example, if a \(.forward)\ file contains
+.display asis
+a.nother@elsewhere.example, /home/spqr/archive
+.endd
+the delivery to \(/home/spqr/archive)\ is done by running the \address@_file\
+transport.
+.display asis
+localuser:
+ driver = accept
+ check_local_user
+ transport = local_delivery
+.endd
+The final router sets up delivery into local mailboxes, provided that the local
+part is the name of a local login, by accepting the address and queuing it for
+the \%local@_delivery%\ transport. Otherwise, we have reached the end of the
+routers, so the address is bounced.
+
+
+.section Transport configuration
+.index default||transports
+.index transports||default
+Transports define mechanisms for actually delivering messages. They operate
+only when referenced from routers, so the order in which they are defined does
+not matter. The transports section of the configuration starts with
+.display asis
+begin transports
+.endd
+One remote transport and four local transports are defined.
+.display asis
+remote_smtp:
+ driver = smtp
+.endd
+This transport is used for delivering messages over SMTP connections. All its
+options are defaulted. The list of remote hosts comes from the router.
+.display asis
+local_delivery:
+ driver = appendfile
+ file = /var/mail/$local_part
+ delivery_date_add
+ envelope_to_add
+ return_path_add
+# group = mail
+# mode = 0660
+.endd
+This \%appendfile%\ transport is used for local delivery to user mailboxes in
+traditional BSD mailbox format. By default it runs under the uid and gid of the
+local user, which requires the sticky bit to be set on the \(/var/mail)\
+directory. Some systems use the alternative approach of running mail deliveries
+under a particular group instead of using the sticky bit. The commented options
+show how this can be done.
+
+Exim adds three headers to the message as it delivers it: ::Delivery-date::,
+::Envelope-to:: and ::Return-path::. This action is requested by the three
+similarly-named options above.
+.display asis
+address_pipe:
+ driver = pipe
+ return_output
+.endd
+This transport is used for handling deliveries to pipes that are generated by
+redirection (aliasing or users' \(.forward)\ files). The \return@_output\
+option specifies that any output generated by the pipe is to be returned to the
+sender.
+.display asis
+address_file:
+ driver = appendfile
+ delivery_date_add
+ envelope_to_add
+ return_path_add
+.endd
+This transport is used for handling deliveries to files that are generated by
+redirection. The name of the file is not specified in this instance of
+\%appendfile%\, because it comes from the \%redirect%\ router.
+.display asis
+address_reply:
+ driver = autoreply
+.endd
+This transport is used for handling automatic replies generated by users'
+filter files.
+
+
+.section Default retry rule
+.index retry||default rule
+.index default||retry rule
+The retry section of the configuration file contains rules which affect the way
+Exim retries deliveries that cannot be completed at the first attempt. It is
+introduced by the line
+.display asis
+begin retry
+.endd
+In the default configuration, there is just one rule, which applies to all
+errors:
+.display asis
+* * F,2h,15m; G,16h,1h,1.5; F,4d,6h
+.endd
+This causes any temporarily failing address to be retried every 15 minutes for
+2 hours, then at intervals starting at one hour and increasing by a factor of
+1.5 until 16 hours have passed, then every 6 hours up to 4 days. If an address
+is not delivered after 4 days of failure, it is bounced.
+
+
+.section Rewriting configuration
+The rewriting section of the configuration, introduced by
+.display asis
+begin rewrite
+.endd
+contains rules for rewriting addresses in messages as they arrive. There are no
+rewriting rules in the default configuration file.
+
+
+.section Authenticators configuration
+.index \\AUTH\\||configuration
+The authenticators section of the configuration, introduced by
+.display asis
+begin authenticators
+.endd
+defines mechanisms for the use of the SMTP \\AUTH\\ command. No authenticators
+are specified in the default configuration file.
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Regular expressions
+.set runningfoot "regular expressions"
+.rset CHAPregexp ~~chapter
+
+.index regular expressions||library
+.index PCRE
+Exim supports the use of regular expressions in many of its options. It
+uses the PCRE regular expression library; this provides regular expression
+matching that is compatible with Perl 5. The syntax and semantics of
+regular expressions is discussed in many Perl reference books, and also in
+Jeffrey Friedl's
+.if ~~html
+[(A HREF="http://www.oreilly.com/catalog/regex/")]
+.fi
+$it{Mastering Regular Expressions}
+.if ~~html
+[(/A)]
+.fi
+(O'Reilly, ISBN 0-596-00289-0).
+
+The documentation for the syntax and semantics of the regular expressions that
+are supported by PCRE is included in plain text in the file
+\(doc/pcrepattern.txt)\ in the Exim distribution, and also in the HTML
+tarbundle of Exim documentation, and as an appendix to the
+.if ~~html
+[(A HREF="http://www.uit.co.uk/exim-book/")]
+.fi
+Exim book.
+.if ~~html
+[(/A)]
+.fi
+It describes in detail the features of the regular expressions that PCRE
+supports, so no further description is included here. The PCRE functions are
+called from Exim using the default option settings (that is, with no PCRE
+options set), except that the \\PCRE@_CASELESS\\ option is set when the
+matching is required to be case-insensitive.
+
+.em
+In most cases, when a regular expression is required in an Exim configuration,
+it has to start with a circumflex, in order to distinguish it from plain text
+or an `ends with' wildcard. In this example of a configuration setting, the
+second item in the colon-separated list is a regular expression.
+.display asis
+domains = a.b.c : ^\\d{3} : *.y.z : ...
+.endd
+The doubling of the backslash is required because of string expansion that
+precedes interpretation -- see section ~~SECTlittext for more discussion of
+this issue, and a way of avoiding the need for doubling backslashes. The
+regular expression that is eventually used in this example contains just one
+backslash. The circumflex is included in the regular expression, and has the
+normal effect of `anchoring' it to the start of the string that is being
+matched.
+
+There are, however, two cases where a circumflex is not required for the
+recognition of a regular expression: these are the \match\ condition in a
+string expansion, and the \matches\ condition in an Exim filter file. In these
+cases, the relevant string is always treated as a regular expression; if it
+does not start with a circumflex, the expression is not anchored, and can match
+anywhere in the subject string.
+
+In all cases, if you want a regular expression to match at the end of a string,
+you must code the @$ metacharacter to indicate this. For example:
+.display asis
+domains = ^\\d{3}\\.example
+.endd
+matches the domain \*123.example*\, but it also matches \*123.example.com*\.
+You need to use:
+.display asis
+domains = ^\\d{3}\\.example\$
+.endd
+if you want \*example*\ to be the top-level domain. (The backslash before the
+@$ is another artefact of string expansion.)
+.nem
+
+
+.section Testing regular expressions
+.index testing||regular expressions
+.index regular expressions||testing
+.index \*pcretest*\
+A program called \*pcretest*\ forms part of the PCRE distribution and is built
+with PCRE during the process of building Exim. It is primarily intended for
+testing PCRE itself, but it can also be used for experimenting with regular
+expressions. After building Exim, the binary can be found in the build
+directory (it is not installed anywhere automatically). There is documentation
+of various options in \(doc/pcretest.txt)\, but for simple testing, none are
+needed. This is the output of a sample run of \*pcretest*\:
+.display
+ re> $cb{/^([^@@]+)@@.+@\.(ac|edu)@\.(?!kr)[a-z]@{2@}@$/}
+data> $cb{x@@y.ac.uk}
+ 0: x@@y.ac.uk
+ 1: x
+ 2: ac
+data> $cb{x@@y.ac.kr}
+No match
+data> $cb{x@@y.edu.com}
+No match
+data> $cb{x@@y.edu.co}
+ 0: x@@y.edu.co
+ 1: x
+ 2: edu
+.endd
+.if ~~sys.fancy
+Input typed by the user is shown in bold face.
+.fi
+After the `re>' prompt, a regular expression enclosed in delimiters is
+expected. If this compiles without error, `data>' prompts are given for strings
+against which the expression is matched. An empty data line causes a new
+regular expression to be read. If the match is successful, the captured
+substring values (that is, what would be in the variables \$0$\, \$1$\, \$2$\,
+etc.) are shown. The above example tests for an email address whose domain ends
+with either `ac' or `edu' followed by a two-character top-level domain that is
+not `kr'. The local part is captured in \$1$\ and the `ac' or `edu' in \$2$\.
+
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter File and database lookups
+.set runningfoot "file/database lookups"
+.rset CHAPfdlookup "~~chapter"
+.index file||lookup
+.index database lookups
+.index lookup||description of
+Exim can be configured to look up data in files or databases as it processes
+messages. Two different kinds of syntax are used:
+.numberpars
+A string that is to be expanded may contain explicit lookup requests. These
+cause parts of the string to be replaced by data that is obtained from the
+lookup.
+.nextp
+Lists of domains, hosts, and email addresses can contain lookup requests as a
+way of avoiding excessively long linear lists. In this case, the data that is
+returned by the lookup is often (but not always) discarded; whether the lookup
+succeeds or fails is what really counts. These kinds of list are described in
+chapter ~~CHAPdomhosaddlists.
+.endp
+It is easy to confuse the two different kinds of lookup, especially as the
+lists that may contain the second kind are always expanded before being
+processed as lists. Therefore, they may also contain lookups of the first kind.
+Be careful to distinguish between the following two examples:
+.display asis
+domains = ${lookup{$sender_host_address}lsearch{/some/file}}
+domains = lsearch;/some/file
+.endd
+The first uses a string expansion, the result of which must be a domain list.
+String expansions are described in detail in chapter ~~CHAPexpand. The
+expansion takes place first, and the file that is searched could contain lines
+like this:
+.display asis
+192.168.3.4: domain1 : domain2 : ...
+192.168.1.9: domain3 : domain4 : ...
+.endd
+Thus, the result of the expansion is a list of domains (and possibly other
+types of item that are allowed in domain lists).
+
+In the second case, the lookup is a single item in a domain list. It causes
+Exim to use a lookup to see if the domain that is being processed can be found
+in the file. The file could contains lines like this:
+.display asis
+domain1:
+domain2:
+.endd
+Any data that follows the keys is not relevant when checking that the domain
+matches the list item.
+
+It is possible to use both kinds of lookup at once. Consider a file containing
+lines like this:
+.display asis
+192.168.5.6: lsearch;/another/file
+.endd
+If the value of \$sender@_host@_address$\ is 192.168.5.6, expansion of the
+first \domains\ setting above generates the second setting, which therefore
+causes a second lookup to occur.
+
+The rest of this chapter describes the different lookup types that are
+available. Any of them can be used in either of the circumstances described
+above. The syntax requirements for the two cases are described in chapters
+~~CHAPexpand and ~~CHAPdomhosaddlists, respectively.
+
+.section Lookup types
+.index lookup||types of
+.index single-key lookup||definition of
+Two different styles of data lookup are implemented:
+.numberpars $.
+The \*single-key*\ style requires the specification of a file in which to look,
+and a single key to search for. The lookup type determines how the file is
+searched.
+.nextp
+.index query-style lookup||definition of
+The \*query*\ style accepts a generalized database query.
+No particular key value is assumed by Exim for query-style lookups. You can
+use whichever Exim variable(s) you need to construct the database query.
+.endp
+The code for each lookup type is in a separate source file that is included in
+the binary of Exim only if the corresponding compile-time option is set. The
+default settings in \(src/EDITME)\ are:
+.display asis
+LOOKUP_DBM=yes
+LOOKUP_LSEARCH=yes
+.endd
+which means that only linear searching and DBM lookups are included by default.
+For some types of lookup (e.g. SQL databases), you need to install appropriate
+libraries and header files before building Exim.
+
+
+
+.section Single-key lookup types
+.rset SECTsinglekeylookups "~~chapter.~~section"
+.index lookup||single-key types
+.index single-key lookup||list of types
+The following single-key lookup types are implemented:
+.numberpars $.
+.index cdb||description of
+.index lookup||cdb
+.index binary zero||in lookup key
+\%cdb%\: The given file is searched as a Constant DataBase file, using the key
+string without a terminating binary zero. The cdb format is designed for
+indexed files that are read frequently and never updated, except by total
+re-creation. As such, it is particulary suitable for large files containing
+aliases or other indexed data referenced by an MTA. Information about cdb can
+be found in several places:
+.display rm
+\?http://www.pobox.com/@~djb/cdb.html?\
+\?ftp://ftp.corpit.ru/pub/tinycdb/?\
+\?http://packages.debian.org/stable/utils/freecdb.html?\
+.endd
+A cdb distribution is not needed in order to build Exim with cdb support,
+because the code for reading cdb files is included directly in Exim itself.
+However, no means of building or testing cdb files is provided with Exim, so
+you need to obtain a cdb distribution in order to do this.
+.nextp
+.index DBM||lookup type
+.index lookup||dbm
+.index binary zero||in lookup key
+\%dbm%\: Calls to DBM library functions are used to extract data from the given
+DBM file by looking up the record with the given key. A terminating binary
+zero is included in the key that is passed to the DBM library. See section
+~~SECTdb for a discussion of DBM libraries.
+.index Berkeley DB library||file format
+For all versions of Berkeley DB, Exim uses the \\DB@_HASH\\ style of database
+when building DBM files using the \exim@_dbmbuild\ utility. However, when using
+Berkeley DB versions 3 or 4, it opens existing databases for reading with the
+\\DB@_UNKNOWN\\ option. This enables it to handle any of the types of database
+that the library supports, and can be useful for accessing DBM files created by
+other applications. (For earlier DB versions, \\DB@_HASH\\ is always used.)
+
+.nextp
+.index lookup||dbmnz
+.index lookup||dbm, terminating zero
+.index binary zero||in lookup key
+.index Courier
+.index \(/etc/userdbshadow.dat)\
+.index dmbnz lookup type
+\%dbmnz%\: This is the same as \%dbm%\, except that a terminating binary zero
+is not included in the key that is passed to the DBM library. You may need this
+if you want to look up data in files that are created by or shared with some
+other application that does not use terminating zeros. For example, you need to
+use \%dbmnz%\ rather than \%dbm%\ if you want to authenticate incoming SMTP
+calls using the passwords from Courier's \(/etc/userdbshadow.dat)\ file. Exim's
+utility program for creating DBM files (\*exim@_dbmbuild*\) includes the zeros
+by default, but has an option to omit them (see section ~~SECTdbmbuild).
+.nextp
+.index lookup||dsearch
+.index dsearch lookup type
+\%dsearch%\: The given file must be a directory; this is searched for a file
+whose name is the key. The key may not contain any forward slash characters.
+The result of a successful lookup is the name of the file. An example of how
+this lookup can be used to support virtual domains is given in section
+~~SECTvirtualdomains.
+.nextp
+.index lookup||iplsearch
+.index iplsearch lookup type
+.em
+\%iplsearch%\: The given file is a text file containing keys and data. A key is
+terminated by a colon or white space or the end of the line. The keys in the
+file must be IP addresses, or IP addresses with CIDR masks. Keys that involve
+IPv6 addresses must be enclosed in quotes to prevent the first internal colon
+being interpreted as a key terminator. For example:
+.display asis
+1.2.3.4: data for 1.2.3.4
+192.168.0.0/16 data for 192.168.0.0/16
+"abcd::cdab": data for abcd::cdab
+"abcd:abcd::/32" data for abcd:abcd::/32
+.endd
+The key for an \%iplsearch%\ lookup must be an IP address (without a mask). The
+file is searched linearly, using the CIDR masks where present, until a matching
+key is found. The first key that matches is used; there is no attempt to find a
+`best' match. Apart from the way the keys are matched, the processing for
+\%iplsearch%\ is the same as for \%lsearch%\.
+
+\**Warning 1**\: Unlike most other single-key lookup types, a file of data for
+\%iplsearch%\ can \*not*\ be turned into a DBM or cdb file, because those
+lookup types support only literal keys.
+
+\**Warning 2**\: In a host list, you must always use \%net-iplsearch%\ so that
+the implicit key is the host's IP address rather than its name (see section
+~~SECThoslispatsikey).
+.nem
+
+.nextp
+.index linear search
+.index lookup||lsearch
+.index lsearch lookup type
+\%lsearch%\: The given file is a text file that is searched linearly for a
+line beginning with the search key, terminated by a colon or white space or the
+end of the line. The first occurrence that is found in the file is used. White
+space between the key and the colon is permitted. The remainder of the line,
+with leading and trailing white space removed, is the data. This can be
+continued onto subsequent lines by starting them with any amount of white
+space, but only a single space character is included in the data at such a
+junction. If the data begins with a colon, the key must be terminated by a
+colon, for example:
+.display
+baduser: :fail:
+.endd
+Empty lines and lines beginning with @# are ignored, even if they occur in the
+middle of an item. This is the traditional textual format of alias files. Note
+that the keys in an \%lsearch%\ file are literal strings. There is no
+wildcarding of any kind.
+
+.index lookup||lsearch, colons in keys
+In most \%lsearch%\ files, keys are not required to contain colons
+.em
+or @# characters, or
+.nem
+whitespace. However, if you need this feature, it is available. If a key begins
+with a doublequote character, it is terminated only by a matching quote (or end
+of line), and the normal escaping rules apply to its contents (see section
+~~SECTstrings). An optional colon is permitted after quoted keys (exactly as
+for unquoted keys). There is no special handling of quotes for the data part of
+an \%lsearch%\ line.
+.nextp
+.index NIS lookup type
+.index lookup||NIS
+.index binary zero||in lookup key
+\%nis%\: The given file is the name of a NIS map, and a NIS lookup is done with
+the given key, without a terminating binary zero. There is a variant called
+\%nis0%\ which does include the terminating binary zero in the key. This is
+reportedly needed for Sun-style alias files. Exim does not recognize NIS
+aliases; the full map names must be used.
+.nextp
+.index wildlsearch lookup type
+.index lookup||wildlsearch
+.index nwildlsearch lookup type
+.index lookup||nwildlsearch
+\%wildlsearch%\ or \%nwildlsearch%\: These search a file linearly, like
+\%lsearch%\, but instead of being interpreted as a literal string, each key may
+be wildcarded. The difference between these two lookup types is that for
+\%wildlsearch%\, each key in the file is string-expanded before being used,
+whereas for \%nwildlsearch%\, no expansion takes place.
+
+Like \%lsearch%\, the testing is done case-insensitively. The following forms
+of wildcard are recognized:
+.numberpars "$*$"
+The string may begin with an asterisk to mean `begins with'. For example:
+.display asis
+*.a.b.c data for anything.a.b.c
+*fish data for anythingfish
+.endd
+.nextp
+The string may begin with a circumflex to indicate a regular expression. For
+example, for \%wildlsearch%\:
+.display asis
+^\N\d+\.a\.b\N data for <digits>.a.b
+.endd
+Note the use of \"@\N"\ to disable expansion of the contents of the regular
+expression. If you are using \%nwildlsearch%\, where the keys are not
+string-expanded, the equivalent entry is:
+.display asis
+^\d+\.a\.b data for <digits>.a.b
+.endd
+
+If the regular expression contains white space or colon characters, you must
+either quote it (see \%lsearch%\ above), or represent these characters in other
+ways. For example, \"@\s"\ can be used for white space and \"@\x3A"\ for a
+colon. This may be easier than quoting, because if you quote, you have to
+escape all the backslashes inside the quotes.
+.nextp
+Although I cannot see it being of much use, the general matching function
+that is used to implement
+\%(n)wildlsearch%\
+means that the string may begin with a lookup name terminated by a semicolon,
+and followed by lookup data. For example:
+.display asis
+cdb;/some/file data for keys that match the file
+.endd
+The data that is obtained from the nested lookup is discarded.
+.endp
+Keys that do not match any of these patterns are interpreted literally. The
+continuation rules for the data are the same as for \%lsearch%\, and keys may
+be followed by optional colons.
+
+\**Warning**\: Unlike most other single-key lookup types, a file of data for
+\%(n)wildlsearch%\ can \*not*\ be turned into a DBM or cdb file, because those
+lookup types support only literal keys.
+.endp
+
+.section Query-style lookup types
+.index lookup||query-style types
+.index query-style lookup||list of types
+The supported query-style lookup types are listed below. Further details about
+many of them are given in later sections.
+.numberpars $.
+.index DNS||as a lookup type
+.index lookup||DNS
+\%dnsdb%\: This does a DNS search for a record whose domain name is the supplied
+query. The resulting data is the contents of the record. See section
+~~SECTdnsdb.
+.nextp
+.index Interbase lookup type
+.index lookup||Interbase
+\%ibase%\: This does a lookup in an Interbase database.
+.nextp
+.index LDAP||lookup type
+.index lookup||LDAP
+\%ldap%\: This does an LDAP lookup using a query in the form of a URL, and
+returns attributes from a single entry. There is a variant called \%ldapm%\
+that permits values from multiple entries to be returned. A third variant
+called \%ldapdn%\ returns the Distinguished Name of a single entry instead of
+any attribute values. See section ~~SECTldap.
+.nextp
+.index MySQL||lookup type
+.index lookup||MySQL
+\%mysql%\: The format of the query is an SQL statement that is passed to a MySQL
+database. See section ~~SECTsql.
+.nextp
+.index NIS@+ lookup type
+.index lookup||NIS+
+\%nisplus%\: This does a NIS+ lookup using a query that can specify the name of
+the field to be returned. See section ~~SECTnisplus.
+.nextp
+.index Oracle||lookup type
+.index lookup||Oracle
+\%oracle%\: The format of the query is an SQL statement that is passed to an
+Oracle database. See section ~~SECTsql.
+.nextp
+.index lookup||passwd
+.index passwd lookup type
+\%passwd%\ is a query-style lookup with queries that are just user names. The
+lookup calls \*getpwnam()*\ to interrogate the system password data, and on
+success, the result string is the same as you would get from an \%lsearch%\
+lookup on a traditional \(/etc/passwd file)\, though with \"*"\ for the
+password value. For example:
+.display asis
+*:42:42:King Rat:/home/kr:/bin/bash
+.endd
+.nextp
+.index PostgreSQL lookup type
+.index lookup||PostgreSQL
+\%pgsql%\: The format of the query is an SQL statement that is passed to a
+PostgreSQL database. See section ~~SECTsql.
+.nextp
+\%testdb%\: This is a lookup type that is used for testing Exim. It is
+not likely to be useful in normal operation.
+.nextp
+.index whoson lookup type
+.index lookup||whoson
+\%whoson%\: \*Whoson*\ (\?http://whoson.sourceforge.net?\) is a proposed
+Internet protocol that allows Internet server programs to check whether a
+particular (dynamically allocated) IP address is currently allocated to a known
+(trusted) user and, optionally, to obtain the identity of the said user. In
+Exim, this can be used to implement `POP before SMTP' checking using ACL
+statements such as
+.display asis
+require condition = \
+ ${lookup whoson {$sender_host_address}{yes}{no}}
+.endd
+The query consists of a single IP address. The value returned is the name of
+the authenticated user.
+.endp
+
+.section Temporary errors in lookups
+.index lookup||temporary error in
+Lookup functions can return temporary error codes if the lookup cannot be
+completed. For example, a NIS or LDAP database might be unavailable. For this
+reason, it is not advisable to use a lookup that might do this for critical
+options such as a list of local domains.
+
+When a lookup cannot be completed in a router or transport, delivery
+of the message (to the relevant address) is deferred, as for any other
+temporary error. In other circumstances Exim may assume the lookup has failed,
+or may give up altogether.
+
+
+.section Default values in single-key lookups
+.rset SECTdefaultvaluelookups "~~chapter.~~section"
+.index wildcard lookups
+.index lookup||default values
+.index lookup||wildcard
+.index lookup||$*$ added to type
+.index default||in single-key lookups
+In this context, a `default value' is a value specified by the administrator
+that is to be used if a lookup fails.
+
+If `$*$' is added to a single-key lookup type (for example, \lsearch$*$\) and
+the initial lookup fails, the key `$*$' is looked up in the file to provide
+a default value. See also the section on partial matching below.
+
+.index @*@@ with single-key lookup
+.index lookup||$*$@@ added to type
+.index alias file||per-domain default
+Alternatively, if `$*$@@' is added to a single-key lookup type (for example
+\dbm$*$@@\) then, if the initial lookup fails and the key contains an @@
+character, a second lookup is done with everything before the last @@ replaced
+by $*$. This makes it possible to provide per-domain defaults in alias files
+that include the domains in the keys. If the second lookup fails (or doesn't
+take place because there is no @@ in the key), `$*$' is looked up.
+For example, a \%redirect%\ router might contain:
+.display asis
+data = ${lookup{$local_part@$domain}lsearch*@{/etc/mixed-aliases}}
+.endd
+Suppose the address that is being processed is \*jane@@eyre.example*\. Exim
+looks up these keys, in this order:
+.display asis
+jane@eyre.example
+*@eyre.example
+*
+.endd
+The data is taken from whichever key it finds first. \**Note**\: in an
+\%lsearch%\ file, this does not mean the first of these keys in the file. A
+complete scan is done for each key, and only if it is not found at all does
+Exim move on to try the next key.
+
+
+.section Partial matching in single-key lookups
+.rset SECTpartiallookup "~~chapter.~~section"
+.index partial matching
+.index wildcard lookups
+.index lookup||partial matching
+.index lookup||wildcard
+.index asterisk||in search type
+The normal operation of a single-key lookup is to search the file for an exact
+match with the given key. However, in a number of situations where domains are
+being looked up, it is useful to be able to do partial matching. In this case,
+information in the file that has a key starting with `$*$.' is matched by any
+domain that ends with the components that follow the full stop. For example, if
+a key in a DBM file is
+.display
+*.dates.fict.example
+.endd
+then when partial matching is enabled this is matched by (amongst others)
+\*2001.dates.fict.example*\ and \*1984.dates.fict.example*\. It is also matched
+by \*dates.fict.example*\, if that does not appear as a separate key in the
+file.
+
+\**Note**\: Partial matching is not available for query-style lookups. It is
+also not available for any lookup items in address lists (see section
+~~SECTaddresslist).
+
+Partial matching is implemented by doing a series of separate lookups using
+keys constructed by modifying the original subject key. This means that it can
+be used with any of the single-key lookup types, provided that
+partial matching keys
+beginning with a special prefix (default `$*$.') are included in the data file.
+Keys in the file that do not begin with the prefix are matched only by
+unmodified subject keys when partial matching is in use.
+
+Partial matching is requested by adding the string `partial-' to the front of
+the name of a single-key lookup type, for example, \partial-dbm\. When this is
+done, the subject key is first looked up unmodified; if that fails, `$*$.'
+is added at the start of the subject key, and it is looked up again. If that
+fails, further lookups are tried with dot-separated components removed
+from the start of the subject key, one-by-one, and `$*$.' added on the front of
+what remains.
+
+A minimum number of two non-$*$ components are required. This can be adjusted
+by including a number before the hyphen in the search type. For example,
+\partial3-lsearch\ specifies a minimum of three non-$*$ components in the
+modified keys. Omitting the number is equivalent to `partial2-'. If the subject
+key is \*2250.dates.fict.example*\ then the following keys are looked up when
+the minimum number of non-$*$ components is two:
+.display asis
+2250.dates.fict.example
+*.2250.dates.fict.example
+*.dates.fict.example
+*.fict.example
+.endd
+As soon as one key in the sequence is successfully looked up, the lookup
+finishes.
+
+.index lookup||partial matching, changing prefix
+.index prefix||for partial matching
+The use of `$*$.' as the partial matching prefix is a default that can be
+changed. The motivation for this feature is to allow Exim to operate with file
+formats that are used by other MTAs. A different prefix can be supplied in
+parentheses instead of the hyphen after `partial'. For example:
+.display asis
+domains = partial(.)lsearch;/some/file
+.endd
+In this example, if the domain is \*a.b.c*\, the sequence of lookups is
+\"a.b.c"\, \".a.b.c"\, and \".b.c"\ (the default minimum of 2 non-wild
+components is unchanged). The prefix may consist of any punctuation characters
+other than a closing parenthesis. It may be empty, for example:
+.display asis
+domains = partial1()cdb;/some/file
+.endd
+For this example, if the domain is \*a.b.c*\, the sequence of lookups is
+\"a.b.c"\, \"b.c"\, and \"c"\.
+
+If `partial0' is specified, what happens at the end (when the lookup with just
+one non-wild component has failed, and the original key is shortened right down
+to the null string) depends on the prefix:
+.numberpars $.
+If the prefix has zero length, the whole lookup fails.
+.nextp
+If the prefix has length 1, a lookup for just the prefix is done. For
+example, the final lookup for `partial0(.)' is for \"."\ alone.
+.nextp
+Otherwise, if the prefix ends in a dot, the dot is removed, and the
+remainder is looked up. With the default prefix, therefore, the final lookup is
+for `$*$' on its own.
+.nextp
+Otherwise, the whole prefix is looked up.
+.endp
+
+If the search type ends in `$*$' or `$*$@@' (see section
+~~SECTdefaultvaluelookups above), the search for an ultimate default that this
+implies happens after all partial lookups have failed. If `partial0' is
+specified, adding `$*$' to the search type has no effect with the default
+prefix, because the `$*$' key is already included in the sequence of partial
+lookups. However, there might be a use for lookup types such as
+`partial0(.)lsearch$*$'.
+
+The use of `$*$' in lookup partial matching differs from its use as a wildcard
+in domain lists and the like. Partial matching works only in terms of
+dot-separated components; a key such as \"*fict.example"\
+in a database file is useless, because the asterisk in a partial matching
+subject key is always followed by a dot.
+
+
+
+.section Lookup caching
+.index lookup||caching
+.index caching||lookup data
+An Exim process
+caches the most recent lookup result on a per-file basis for single-key
+lookup types, and keeps the relevant files open. In some types of configuration
+this can lead to many files being kept open for messages with many recipients.
+To avoid hitting the operating system limit on the number of simultaneously
+open files, Exim closes the least recently used file when it needs to open more
+files than its own internal limit, which can be changed via the
+\lookup@_open@_max\ option.
+
+For query-style lookups, a single data cache per lookup type is kept. The files
+are closed and the caches flushed at strategic points during delivery -- for
+example, after all routing is complete.
+
+
+.section Quoting lookup data
+.index lookup||quoting
+.index quoting||in lookups
+When data from an incoming message is included in a query-style lookup, there
+is the possibility of special characters in the data messing up the syntax of
+the query. For example, a NIS+ query that contains
+.display asis
+[name=$local_part]
+.endd
+will be broken if the local part happens to contain a closing square bracket.
+For NIS+, data can be enclosed in double quotes like this:
+.display asis
+[name="$local_part"]
+.endd
+but this still leaves the problem of a double quote in the data. The rule for
+NIS+ is that double quotes must be doubled. Other lookup types have different
+rules, and to cope with the differing requirements, an expansion operator
+of the following form is provided:
+.display
+@$@{quote@_<<lookup-type>>:<<string>>@}
+.endd
+For example, the safest way to write the NIS+ query is
+.display asis
+[name="${quote_nisplus:$local_part}"]
+.endd
+See chapter ~~CHAPexpand for full coverage of string expansions. The quote
+operator can be used for all lookup types, but has no effect for single-key
+lookups, since no quoting is ever needed in their key strings.
+
+
+
+.section More about dnsdb
+.rset SECTdnsdb "~~chapter.~~section"
+.index dnsdb lookup
+.index lookup||dnsdb
+.index DNS||as a lookup type
+The \%dnsdb%\ lookup type uses the DNS as its database. A query consists of a
+record type and a domain name, separated by an equals sign. For example, an
+expansion string could contain:
+.display asis
+${lookup dnsdb{mx=a.b.example}{$value}fail}
+.endd
+.em
+The supported record types are A, CNAME, MX, NS, PTR, SRV, and TXT,
+.nem
+and, when Exim is compiled with IPv6 support, AAAA (and A6 if that is also
+configured). If no type is given, TXT is assumed. When the type is PTR, the
+address should be given as normal; it is converted to the necessary inverted
+format internally. For example:
+.display asis
+${lookup dnsdb{ptr=192.168.4.5}{$value}fail}
+.endd
+
+.index MX record||in \%dnsdb%\ lookup
+For MX records, both the preference value and the host name are returned,
+separated by a space.
+.em
+.index SRV record||in \%dnsdb%\ lookup
+For SRV records, the priority, weight, port, and host name are returned,
+separated by spaces. For any record type,
+.nem
+if multiple records are found (or, for A6 lookups, if a single record leads to
+multiple addresses), the data is returned as a concatenation, separated by
+newlines. The order, of course, depends on the DNS resolver.
+
+
+
+
+.section More about LDAP
+.rset SECTldap "~~chapter.~~section"
+.index LDAP lookup
+.index lookup||LDAP
+.index Solaris||LDAP
+The original LDAP implementation came from the University of Michigan; this has
+become `Open LDAP', and there are now two different releases. Another
+implementation comes from Netscape, and Solaris 7 and subsequent releases
+contain inbuilt LDAP support. Unfortunately, though these are all compatible at
+the lookup function level, their error handling is different. For this reason
+it is necessary to set a compile-time variable when building Exim with LDAP, to
+indicate which LDAP library is in use. One of the following should appear in
+your \(Local/Makefile)\:
+.display asis
+LDAP_LIB_TYPE=UMICHIGAN
+LDAP_LIB_TYPE=OPENLDAP1
+LDAP_LIB_TYPE=OPENLDAP2
+LDAP_LIB_TYPE=NETSCAPE
+LDAP_LIB_TYPE=SOLARIS
+.endd
+If \\LDAP@_LIB@_TYPE\\ is not set, Exim assumes \"OPENLDAP1"\, which has the
+same interface as the University of Michigan version.
+
+There are three LDAP lookup types in Exim. These behave slightly differently in
+the way they handle the results of a query:
+.numberpars $.
+\%ldap%\ requires the result to contain just one entry; if there are more, it
+gives an error.
+.nextp
+\%ldapdn%\ also requires the result to contain just one entry, but it is the
+Distinguished Name that is returned rather than any attribute values.
+.nextp
+\%ldapm%\ permits the result to contain more than one entry; the attributes from
+all of them are returned.
+.endp
+
+For \%ldap%\ and \%ldapm%\, if a query finds only entries with no attributes,
+Exim behaves as if the entry did not exist, and the lookup fails. The format of
+the data returned by a successful lookup is described in the next section.
+First we explain how LDAP queries are coded.
+
+.section Format of LDAP queries
+.rset SECTforldaque "~~chapter.~~section"
+.index LDAP||query format
+An LDAP query takes the form of a URL as defined in RFC 2255. For example, in
+the configuration of a \%redirect%\ router one might have this setting:
+.display asis
+data = ${lookup ldap \
+ {ldap:///cn=$local_part,o=University%20of%20Cambridge,\
+ c=UK?mailbox?base?}}
+.endd
+.index LDAP||with TLS
+The URL may begin with \"ldap"\ or \"ldaps"\ if your LDAP library supports
+secure (encrypted) LDAP connections. The second of these ensures that an
+encrypted TLS connection is used.
+
+.section LDAP quoting
+.index LDAP||quoting
+Two levels of quoting are required in LDAP queries, the first for LDAP itself
+and the second because the LDAP query is represented as a URL. Furthermore,
+within an LDAP query, two different kinds of quoting are required. For this
+reason, there are two different LDAP-specific quoting operators.
+
+The \quote@_ldap\ operator is designed for use on strings that are part of
+filter specifications. Conceptually, it first does the following conversions on
+the string:
+.display asis
+* => \2A
+( => \28
+) => \29
+\ => \5C
+.endd
+in accordance with RFC 2254. The resulting string is then quoted according
+to the rules for URLs, that is, all characters except
+.display asis
+! $ ' - . _ ( ) * +
+.endd
+are converted to their hex values, preceded by a percent sign. For example:
+.display asis
+${quote_ldap: a(bc)*, a<yz>; }
+.endd
+yields
+.display asis
+%20a%5C28bc%5C29%5C2A%2C%20a%3Cyz%3E%3B%20
+.endd
+Removing the URL quoting, this is (with a leading and a trailing space):
+.display asis
+a\28bc\29\2A, a<yz>;
+.endd
+
+The \quote@_ldap@_dn\ operator is designed for use on strings that are part of
+base DN specifications in queries. Conceptually, it first converts the string
+by inserting a backslash in front of any of the following characters:
+.display asis
+, + " \ < > ;
+.endd
+It also inserts a backslash before any leading spaces or @# characters, and
+before any trailing spaces. (These rules are in RFC 2253.) The resulting string
+is then quoted according to the rules for URLs. For example:
+.display asis
+${quote_ldap_dn: a(bc)*, a<yz>; }
+.endd
+yields
+.display asis
+%5C%20a(bc)*%5C%2C%20a%5C%3Cyz%5C%3E%5C%3B%5C%20
+.endd
+Removing the URL quoting, this is (with a trailing space):
+.display asis
+\ a(bc)*\, a\<yz\>\;\
+.endd
+There are some further comments about quoting in the section on LDAP
+authentication below.
+
+.section LDAP connections
+.index LDAP||connections
+The connection to an LDAP server may either be over TCP/IP, or, when OpenLDAP
+is in use, via a Unix domain socket. The example given above does not specify
+an LDAP server. A server that is reached by TCP/IP can be specified in a query
+by starting it with
+.display
+ldap://<<hostname>>:<<port>>/...
+.endd
+If the port (and preceding colon) are omitted, the standard LDAP port (389) is
+used. When no server is specified in a query, a list of default servers is
+taken from the \ldap@_default@_servers\ configuration option. This supplies a
+colon-separated list of servers which are tried in turn until one successfully
+handles a query, or there is a serious error. Successful handling either
+returns the requested data, or indicates that it does not exist. Serious errors
+are syntactical, or multiple values when only a single value is expected.
+Errors which cause the next server to be tried are connection failures, bind
+failures, and timeouts.
+
+For each server name in the list, a port number can be given. The standard way
+of specifing a host and port is to use a colon separator (RFC 1738). Because
+\ldap@_default@_servers\ is a colon-separated list, such colons have to be
+doubled. For example
+.display asis
+ldap_default_servers = ldap1.example.com::145:ldap2.example.com
+.endd
+If \ldap@_default@_servers\ is unset, a URL with no server name is passed
+to the LDAP library with no server name, and the library's default (normally
+the local host) is used.
+
+If you are using the OpenLDAP library, you can connect to an LDAP server using
+a Unix domain socket instead of a TCP/IP connection. This is specified by using
+\"ldapi"\ instead of \"ldap"\ in LDAP queries. What follows here applies only
+to OpenLDAP. If Exim is compiled with a different LDAP library, this feature is
+not available.
+
+For this type of connection, instead of a host name for the server, a pathname
+for the socket is required, and the port number is not relevant. The pathname
+can be specified either as an item in \ldap@_default@_servers\, or inline in
+the query. In the former case, you can have settings such as
+.display asis
+ldap_default_servers = /tmp/ldap.sock : backup.ldap.your.domain
+.endd
+When the pathname is given in the query, you have to escape the slashes as
+\"%2F"\ to fit in with the LDAP URL syntax. For example:
+.display asis
+${lookup ldap {ldapi://%2Ftmp%2Fldap.sock/o=...
+.endd
+When Exim processes an LDAP lookup and finds that the `hostname' is really
+a pathname, it uses the Unix domain socket code, even if the query actually
+specifies \"ldap"\ or \"ldaps"\. In particular, no encryption is used for a
+socket connection. This behaviour means that you can use a setting of
+\ldap@_default@_servers\ such as in the example above with traditional \"ldap"\
+or \"ldaps"\ queries, and it will work. First, Exim tries a connection via
+the Unix domain socket; if that fails, it tries a TCP/IP connection to the
+backup host.
+
+If an explicit \"ldapi"\ type is given in a query when a host name is
+specified, an error is diagnosed. However, if there are more items in
+\ldap@_default@_servers\, they are tried. In other words:
+.numberpars $.
+Using a pathname with \"ldap"\ or \"ldaps"\ forces the use of the Unix domain
+interface.
+.nextp
+Using \"ldapi"\ with a host name causes an error.
+.endp
+
+Using \"ldapi"\ with no host or path in the query, and no setting of
+\ldap@_default@_servers\, does whatever the library does by default.
+
+
+.section LDAP authentication and control information
+.index LDAP||authentication
+The LDAP URL syntax provides no way of passing authentication and other control
+information to the server. To make this possible, the URL in an LDAP query may
+be preceded by any number of `<<name>>=<<value>>' settings, separated by
+spaces. If a value contains spaces it must be enclosed in double quotes, and
+when double quotes are used, backslash is interpreted in the usual way inside
+them.
+
+The following names are recognized:
+.display
+CONNECT $rm{set a connection timeout}
+.newline
+DEREFERENCE $rm{set the dereferencing parameter}
+USER $rm{set the DN, for authenticating the LDAP bind}
+PASS $rm{set the password, likewise}
+SIZE $rm{set the limit for the number of entries returned}
+TIME $rm{set the maximum waiting time for a query}
+.endd
+The value of the \\DEREFERENCE\\ parameter must be one of the words `never',
+`searching', `finding', or `always'.
+
+Here is an example of an LDAP query in an Exim lookup that uses some of these
+values. This is a single line, folded for ease of reading:
+.display asis
+.indent 0
+${lookup ldap
+ {user="cn=manager,o=University of Cambridge,c=UK" pass=secret
+ ldap:///o=University%20of%20Cambridge,c=UK?sn?sub?(cn=foo)}
+ {$value}fail}
+.endd
+The encoding of spaces as %20 is a URL thing which should not be done for any
+of the auxiliary data. Exim configuration settings that include lookups which
+contain password information should be preceded by `hide' to prevent non-admin
+users from using the \-bP-\ option to see their values.
+
+The auxiliary data items may be given in any order. The default is no
+connection timeout (the system timeout is used), no user or password, no limit
+on the number of entries returned, and no time limit on queries.
+
+The time limit for connection is given in seconds; zero means use the default.
+This facility is available in Netscape SDK 4.1; it may not be available in
+other LDAP implementations. Exim uses the given value if
+\\LDAP@_X@_OPT@_CONNECT@_TIMEOUT\\ is defined in the LDAP headers.
+
+When a DN is quoted in the \\USER=\\ setting for LDAP authentication, Exim
+removes any URL quoting that it may contain before passing it LDAP. Apparently
+some libraries do this for themselves, but some do not. Removing the URL
+quoting has two advantages:
+.numberpars $.
+It makes it possible to use the same \quote@_ldap@_dn\ expansion for \\USER=\\
+DNs as with DNs inside actual queries.
+.nextp
+It permits spaces inside \\USER=\\ DNs.
+.endp
+For example, a setting such as
+.display asis
+USER=cn=${quote_ldap_dn:$1}
+.endd
+should work even if \$1$\ contains spaces.
+
+Expanded data for the \\PASS=\\ value should be quoted using the \quote\
+expansion operator, rather than the LDAP quote operators. The only reason this
+field needs quoting is to ensure that it conforms to the Exim syntax, which
+does not allow unquoted spaces. For example:
+.display asis
+PASS=${quote:$3}
+.endd
+
+The LDAP authentication mechanism can be used to check passwords as part of
+SMTP authentication. See the \ldapauth\ expansion string condition in chapter
+~~CHAPexpand.
+
+
+.section Format of data returned by LDAP
+.index LDAP||returned data formats
+The \%ldapdn%\ lookup type returns the Distinguished Name from a single entry as
+a sequence of values, for example
+.display asis
+cn=manager, o=University of Cambridge, c=UK
+.endd
+
+The \%ldap%\ lookup type generates an error if more than one entry matches the
+search filter, whereas \%ldapm%\ permits this case, and inserts a newline in the
+result between the data from different entries. It is possible for multiple
+values to be returned for both \%ldap%\ and \%ldapm%\, but in the former case you
+know that whatever values are returned all came from a single entry in the
+directory.
+
+In the common case where you specify a single attribute in your LDAP query, the
+result is not quoted, and does not contain the attribute name. If the attribute
+has multiple values, they are separated by commas.
+
+If you specify multiple attributes, the result contains space-separated, quoted
+strings, each preceded by the attribute name and an equals sign. Within the
+quotes, the quote character, backslash, and newline are escaped with
+backslashes, and commas are used to separate multiple values for the attribute.
+Apart from the escaping, the string within quotes takes the same form as the
+output when a single attribute is requested. Specifying no attributes is the
+same as specifying all of an entry's attributes.
+
+Here are some examples of the output format. The first line of each pair is an
+LDAP query, and the second is the data that is returned. The attribute called
+\attr1\ has two values, whereas \attr2\ has only one value:
+.display asis
+ldap:///o=base?attr1?sub?(uid=fred)
+value1.1, value1.2
+
+ldap:///o=base?attr2?sub?(uid=fred)
+value two
+
+ldap:///o=base?attr1,attr2?sub?(uid=fred)
+attr1="value1.1, value1.2" attr2="value two"
+
+ldap:///o=base??sub?(uid=fred)
+objectClass="top" attr1="value1.1, value1.2" attr2="value two"
+.endd
+The \extract\ operator in string expansions can be used to pick out individual
+fields from data that consists of $it{key}=$it{value} pairs. You can make use
+of Exim's \-be-\ option to run expansion tests and thereby check the results of
+LDAP lookups.
+
+
+
+.section More about NIS+
+.rset SECTnisplus "~~chapter.~~section"
+.index NIS@+ lookup type
+.index lookup||NIS+
+NIS+ queries consist of a NIS+ \*indexed name*\ followed by an optional colon
+and field name. If this is given, the result of a successful query is the
+contents of the named field; otherwise the result consists of a concatenation
+of \*field-name=field-value*\ pairs, separated by spaces. Empty values and
+values containing spaces are quoted. For example, the query
+.display asis
+[name=mg1456],passwd.org_dir
+.endd
+might return the string
+.display asis
+name=mg1456 passwd="" uid=999 gid=999 gcos="Martin Guerre"
+home=/home/mg1456 shell=/bin/bash shadow=""
+.endd
+(split over two lines here to fit on the page), whereas
+.display asis
+[name=mg1456],passwd.org_dir:gcos
+.endd
+would just return
+.display asis
+Martin Guerre
+.endd
+with no quotes. A NIS+ lookup fails if NIS+ returns more than one table entry
+for the given indexed key. The effect of the \quote@_nisplus\ expansion
+operator is to double any quote characters within the text.
+
+
+.section More about MySQL, PostgreSQL, Oracle, and Interbase
+.rset SECTsql "~~chapter.~~section"
+.index MySQL||lookup type
+.index PostgreSQL lookup type
+.index lookup||MySQL
+.index lookup||PostgreSQL
+.index Oracle||lookup type
+.index lookup||Oracle
+.index Interbase lookup type
+.index lookup||Interbase
+If any MySQL, PostgreSQL, Oracle, or Interbase lookups are used, the
+\mysql@_servers\, \pgsql@_servers\, \oracle@_servers\, or \ibase@_servers\
+option (as appropriate) must be set to a colon-separated list of server
+information. Each item in the list is a slash-separated list of four items:
+host name, database name, user name, and password. In the case of Oracle, the
+host name field is used for the `service name', and the database name field is
+not used and should be empty. For example:
+.display asis
+hide oracle_servers = oracle.plc.example//ph10/abcdwxyz
+.endd
+Because password data is sensitive, you should always precede the setting with
+`hide', to prevent non-admin users from obtaining the setting via the \-bP-\
+option. Here is an example where two MySQL servers are listed:
+.display asis
+hide mysql_servers = localhost/users/root/secret:\
+ otherhost/users/root/othersecret
+.endd
+For MySQL and PostgreSQL, a host may be specified as <<name>>:<<port>> but
+because this is a colon-separated list, the colon has to be doubled.
+
+For each query, these parameter groups are tried in order until a connection
+and a query succeeds. Queries for these databases are SQL statements, so an
+example might be
+.display asis
+.indent 0
+${lookup mysql{select mailbox from users where id='ph10'}{$value}fail}
+.endd
+If the result of the query contains more than one field, the data for
+each field in the row is returned, preceded by its name, so the result
+of
+.display asis
+.indent 0
+${lookup pgsql{select home,name from users where id='ph10'}{$value}}
+.endd
+might be
+.display asis
+home=/home/ph10 name="Philip Hazel"
+.endd
+Values containing spaces and empty values are double quoted, with embedded
+quotes escaped by a backslash.
+
+If the result of the query contains just one field, the value is passed back
+verbatim, without a field name, for example:
+.display asis
+Philip Hazel
+.endd
+If the result of the query yields more than one row, it is all concatenated,
+with a newline between the data for each row.
+
+The \quote@_mysql\, \quote@_pgsql\, and \quote@_oracle\ expansion operators
+convert newline, tab, carriage return, and backspace to @\n, @\t, @\r, and @\b
+respectively, and the characters single-quote, double-quote, and backslash
+itself are escaped with backslashes. The \quote@_pgsql\ expansion operator, in
+addition, escapes the percent and underscore characters. This cannot be done
+for MySQL because these escapes are not recognized in contexts where these
+characters are not special.
+
+
+.section Special MySQL features
+For MySQL, an empty host name or the use of `localhost' in \mysql@_servers\
+causes a connection to the server on the local host by means of a Unix domain
+socket. An alternate socket can be specified in parentheses. The full syntax of
+each item in \mysql@_servers\ is:
+.display
+<<hostname>>@:@:<<port>>(<<socket name>>)/<<database>>/<<user>>/<<password>>
+.endd
+Any of the three sub-parts of the first field can be omitted. For normal use on
+the local host it can be left blank or set to just `localhost'.
+
+No database need be supplied -- but if it is absent here, it must be given in
+the queries.
+
+If a MySQL query is issued that does not request any data (an insert, update,
+or delete command), the result of the lookup is the number of rows affected.
+
+
+
+.section Special PostgreSQL features
+PostgreSQL lookups can also use Unix domain socket connections to the database.
+This is usually faster and costs less CPU time than a TCP/IP connection.
+However it can be used only if the mail server runs on the same machine as the
+database server. A configuration line for PostgreSQL via Unix domain sockets
+looks like this:
+.display asis
+hide pgsql_servers = (/tmp/.s.PGSQL.5432)/db/user/password : ...
+.endd
+In other words, instead of supplying a host name, a path to the socket is
+given. The path name is enclosed in parentheses so that its slashes aren't
+visually confused with the delimiters for the other server parameters.
+
+If a PostgreSQL query is issued that does not request any data (an insert,
+update, or delete command), the result of the lookup is the number of rows
+affected.
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Domain, host, address, and local part lists
+.set runningfoot "domain, host, and address lists"
+.rset CHAPdomhosaddlists "~~chapter"
+.index list||of domains, hosts, etc.
+A number of Exim configuration options contain lists of domains, hosts,
+email addresses, or local parts. For example, the \hold@_domains\ option
+contains a list of domains whose delivery is currently suspended. These lists
+are also used as data in ACL statements (see chapter ~~CHAPACL).
+
+Each item in one of these lists is a pattern to be matched against a domain,
+host, email address, or local part, respectively. In the sections below, the
+different types of pattern for each case are described, but first we cover some
+general facilities that apply to all four kinds of list.
+
+
+.section Expansion of lists
+.index expansion||of lists
+Each list is expanded as a single string before it is used. If the expansion is
+forced to fail, Exim behaves as if the item it is testing (domain, host,
+address, or local part) is not in the list. Other expansion failures cause
+temporary errors.
+
+If an item in a list is a regular expression, backslashes, dollars and possibly
+other special characters in the expression must be protected against
+misinterpretation by the string expander. The easiest way to do this is to use
+the \"@\N"\ expansion feature to indicate that the contents of the regular
+expression should not be expanded. For example, in an ACL you might have:
+.display asis
+deny senders = \N^\d{8}\w@.*\.baddomain\.example$\N :
+ ${lookup{$domain}lsearch{/badsenders/bydomain}}
+.endd
+The first item is a regular expression that is protected from expansion by
+\"@\N"\, whereas the second uses the expansion to obtain a list of unwanted
+senders based on the receiving domain.
+
+After expansion, the list is split up into separate items for matching.
+Normally, colon is used as the separator character, but this can be varied if
+necessary, as described in section ~~SECTlistconstruct.
+
+
+.section Negated items in lists
+.index list||negation
+.index negation in lists
+Items in a list may be positive or negative. Negative items are indicated by a
+leading exclamation mark, which may be followed by optional white space. A list
+defines a set of items (domains, etc). When Exim processes one of these lists,
+it is trying to find out whether a domain, host, address, or local part
+(respectively) is in the set that is defined by the list. It works like this:
+
+The list is scanned from left to right. If a positive item is matched, the
+subject that is being checked is in the set; if a negative item is matched, the
+subject is not in the set. If the end of the list is reached without the
+subject having matched any of the patterns, it is in the set if the last item
+was a negative one, but not if it was a positive one. For example, the list in
+.display asis
+domainlist relay_domains = !a.b.c : *.b.c
+.endd
+matches any domain ending in \*.b.c*\ except for \*a.b.c*\. Domains that match
+neither \*a.b.c*\ nor \*@*.b.c*\ do not match, because the last item in the
+list is positive. However, if the setting were
+.display asis
+domainlist relay_domains = !a.b.c
+.endd
+then all domains other than \*a.b.c*\ would match because the last item in the
+list is negative. In other words, a list that ends with a negative item behaves
+as if it had an extra item \":*"\ on the end.
+
+Another way of thinking about positive and negative items in lists is to read
+the connector as `or' after a positive item and as `and' after a negative
+item.
+
+
+.section File names in lists
+.rset SECTfilnamlis "~~chapter.~~section"
+.index list||file name in
+If an item in a domain, host, address, or local part list is an absolute file
+name (beginning with a slash character), each line of the file is read and
+processed as if it were an independent item in the list, except that further
+file names are not allowed,
+and no expansion of the data from the file takes place.
+Empty lines in the file are ignored, and the file may also contain comment
+lines:
+.numberpars $.
+For domain and host lists, if a @# character appears anywhere in a line of the
+file, it and all following characters are ignored.
+.nextp
+Because local parts may legitimately contain @# characters, a comment in an
+address list or local part list file is recognized only if @# is preceded by
+white space or the start of the line. For example:
+.display asis
+not#comment@x.y.z # but this is a comment
+.endd
+.endp
+Putting a file name in a list has the same effect as inserting each line of the
+file as an item in the list (blank lines and comments excepted). However, there
+is one important difference: the file is read each time the list is processed,
+so if its contents vary over time, Exim's behaviour changes.
+
+If a file name is preceded by an exclamation mark, the sense of any match
+within the file is inverted. For example, if
+.display asis
+hold_domains = !/etc/nohold-domains
+.endd
+and the file contains the lines
+.display asis
+!a.b.c
+*.b.c
+.endd
+then \*a.b.c*\ is in the set of domains defined by \hold@_domains\, whereas any
+domain matching \"*.b.c"\ is not.
+
+
+.section An lsearch file is not an out-of-line list
+As will be described in the sections that follow, lookups can be used in lists
+to provide indexed methods of checking list membership. There has been some
+confusion about the way \%lsearch%\ lookups work in lists. Because
+an \%lsearch%\ file contains plain text and is scanned sequentially, it is
+sometimes thought that it is allowed to contain wild cards and other kinds of
+non-constant pattern. This is not the case. The keys in an \%lsearch%\ file are
+always fixed strings, just as for any other single-key lookup type.
+
+If you want to use a file to contain wild-card patterns that form part of a
+list, just give the file name on its own, without a search type, as described
+in the previous section.
+
+
+
+.section Named lists
+.rset SECTnamedlists "~~chapter.~~section"
+.index named lists
+.index list||named
+A list of domains, hosts, email addresses, or local parts can be given a name
+which is then used to refer to the list elsewhere in the configuration. This is
+particularly convenient if the same list is required in several different
+places. It also allows lists to be given meaningful names, which can improve
+the readability of the configuration. For example, it is conventional to define
+a domain list called \*local@_domains*\ for all the domains that are handled
+locally on a host, using a configuration line such as
+.display asis
+domainlist local_domains = localhost:my.dom.example
+.endd
+Named lists are referenced by giving their name preceded by a plus sign, so,
+for example, a router that is intended to handle local domains would be
+configured with the line
+.display asis
+domains = +local_domains
+.endd
+The first router in a configuration is often one that handles all domains
+except the local ones, using a configuration with a negated item like this:
+.display asis
+dnslookup:
+ driver = dnslookup
+ domains = ! +local_domains
+ transport = remote_smtp
+ no_more
+.endd
+The four kinds of named list are created by configuration lines starting with
+the words \domainlist\, \hostlist\, \addresslist\, or \localpartlist\,
+respectively. Then there follows the name that you are defining, followed by an
+equals sign and the list itself. For example:
+.display asis
+hostlist relay_hosts = 192.168.23.0/24 : my.friend.example
+addresslist bad_senders = cdb;/etc/badsenders
+.endd
+A named list may refer to other named lists:
+.display asis
+domainlist dom1 = first.example : second.example
+domainlist dom2 = +dom1 : third.example
+domainlist dom3 = fourth.example : +dom2 : fifth.example
+.endd
+
+\**Warning**\: If the last item in a referenced list is a negative one, the
+effect may not be what you intended, because the negation does not propagate
+out to the higher level. For example, consider:
+.display asis
+domainlist dom1 = !a.b
+domainlist dom2 = +dom1 : *.b
+.endd
+The second list specifies `either in the \dom1\ list or \*@*.b*\'. The first
+list specifies just `not \*a.b*\', so the domain \*x.y*\ matches it. That means
+it matches the second list as well. The effect is not the same as
+.display asis
+domainlist dom2 = !a.b : *.b
+.endd
+where \*x.y*\ does not match. It's best to avoid negation altogether in
+referenced lists if you can.
+
+Named lists may have a performance advantage. When Exim is routing an
+address or checking an incoming message, it caches the result of tests on named
+lists. So, if you have a setting such as
+.display asis
+domains = +local_domains
+.endd
+on several of your routers
+or in several ACL statements,
+the actual test is done only for the first one. However, the caching works only
+if there are no expansions within the list itself or any sublists that it
+references. In other words, caching happens only for lists that are known to be
+the same each time they are referenced.
+
+By default, there may be up to 16 named lists of each type. This limit can be
+extended by changing a compile-time variable. The use of domain and host lists
+is recommended for concepts such as local domains, relay domains, and relay
+hosts. The default configuration is set up like this.
+
+
+.section Named lists compared with macros
+.index list||named compared with macro
+.index macro||compared with named list
+At first sight, named lists might seem to be no different from macros in the
+configuration file. However, macros are just textual substitutions. If you
+write
+.display asis
+ALIST = host1 : host2
+auth_advertise_hosts = !ALIST
+.endd
+it probably won't do what you want, because that is exactly the same as
+.display asis
+auth_advertise_hosts = !host1 : host2
+.endd
+Notice that the second host name is not negated. However, if you use a host
+list, and write
+.display asis
+hostlist alist = host1 : host2
+auth_advertise_hosts = ! +alist
+.endd
+the negation applies to the whole list, and so that is equivalent to
+.display asis
+auth_advertise_hosts = !host1 : !host2
+.endd
+
+
+.em
+.section Named list caching
+.index list||caching of named
+.index caching||named lists
+While processing a message, Exim caches the result of checking a named list if
+it is sure that the list is the same each time. In practice, this means that
+the cache operates only if the list contains no @$ characters, which guarantees
+that it will not change when it is expanded. Sometimes, however, you may have
+an expanded list that you know will be the same each time within a given
+message. For example:
+.display asis
+domainlist special_domains = \
+ ${lookup{$sender_host_address}cdb{/some/file}}
+.endd
+This provides a list of domains that depends only on the sending host's IP
+address. If this domain list is referenced a number of times (for example,
+in several ACL lines, or in several routers) the result of the check is not
+cached by default, because Exim does not know that it is going to be the
+same list each time.
+
+By appending \"@_cache"\ to \"domainlist"\ you can tell Exim to go ahead and
+cache the result anyway. For example:
+.display asis
+domainlist_cache special_domains = ${lookup{...
+.endd
+If you do this, you should be absolutely sure that caching is going to do
+the right thing in all cases. When in doubt, leave it out.
+.nem
+
+
+.section Domain lists
+.rset SECTdomainlist "~~chapter.~~section"
+.index domain list||patterns for
+.index list||domain list
+Domain lists contain patterns that are to be matched against a mail domain.
+The following types of item may appear in domain lists:
+.numberpars $.
+.index primary host name
+.index host||name, matched in domain list
+.index \primary@_hostname\
+.index domain list||matching primary host name
+.index @@ in a domain list
+If a pattern consists of a single @@ character, it matches the local host name,
+as set by the \primary@_hostname\ option (or defaulted). This makes it possible
+to use the same configuration file on several different hosts that differ only
+in their names.
+.nextp
+.index @@[] in a domain list
+.index domain list||matching local IP interfaces
+.index domain literal
+If a pattern consists of the string \"@@[]"\ it matches any local IP interface
+address, enclosed in square brackets, as in an email address that contains a
+domain literal.
+.em
+In today's Internet, the use of domain literals is controversial.
+.nem
+.nextp
+.index @@mx@_any
+.index @@mx@_primary
+.index @@mx@_secondary
+.index domain list||matching MX pointers to local host
+If a pattern consists of the string \"@@mx@_any"\ it matches any domain that
+has an MX record pointing to the local host or to any host that is listed in
+.index \hosts@_treat@_as@_local\
+\hosts@_treat@_as@_local\. The items \"@@mx@_primary"\ and \"@@mx@_secondary"\
+are similar, except that the first matches only when a primary MX target is the
+local host, and the second only when no primary MX target is the local host,
+but a secondary MX target is. `Primary' means an MX record with the lowest
+preference value -- there may of course be more than one of them.
+
+.em
+The MX lookup that takes place when matching a pattern of this type is
+performed with the resolver options for widening names turned off. Thus, for
+example, a single-component domain will \*not*\ be expanded by adding the
+resolver's default domain. See the \qualify@_single\ and \search@_parents\
+options of the \%dnslookup%\ router for a discussion of domain widening.
+
+Sometimes you may want to ignore certain IP addresses when using one of these
+patterns. You can specify this by following the pattern with \"/ignore=<<ip
+list>>"\, where <<ip list>> is a list of IP addresses. These addresses are
+ignored when processing the pattern (compare the \ignore@_target@_hosts\ option
+on a router). For example:
+.display asis
+domains = @mx_any/ignore=127.0.0.1
+.endd
+This example matches any domain that has an MX record pointing to one of
+the local host's IP addresses other than 127.0.0.1.
+
+The list of IP addresses is in fact processed by the same code that processes
+host lists, so it may contain CIDR-coded network specifications and it may also
+contain negative items.
+
+Because the list of IP addresses is a sublist within a domain list, you have to
+be careful about delimiters if there is more than one address. Like any other
+list, the default delimiter can be changed. Thus, you might have:
+.display asis
+domains = @mx_any/ignore=<;127.0.0.1;0.0.0.0 : \
+ an.other.domain : ...
+.endd
+so that the sublist uses semicolons for delimiters. When IPv6 addresses are
+involved, it is easiest to change the delimiter for the main list as well:
+.display asis
+domains = <? @mx_any/ignore=<;127.0.0.1;::1 ? \
+ an.other.domain ? ...
+.endd
+.nem
+
+.nextp
+.index asterisk||in domain list
+.index domain list||asterisk in
+.index domain list||matching `ends with'
+If a pattern starts with an asterisk, the remaining characters of the pattern
+are compared with the terminating characters of the domain. The use of `$*$' in
+domain lists differs from its use in partial matching lookups. In a domain
+list, the character following the asterisk need not be a dot, whereas partial
+matching works only in terms of dot-separated components. For example, a domain
+list item such as \"*key.ex"\ matches \*donkey.ex*\ as well as
+\*cipher.key.ex*\.
+.nextp
+.index regular expressions||in domain list
+.index domain list||matching regular expression
+If a pattern starts with a circumflex character, it is treated as a regular
+expression, and matched against the domain using a regular expression matching
+function. The circumflex is treated as part of the regular expression.
+References to descriptions of the syntax of regular expressions are given in
+chapter ~~CHAPregexp.
+
+\**Warning**\: Because domain lists are expanded before being processed, you
+must escape any backslash and dollar characters in the regular expression, or
+use the special \"@\N"\ sequence (see chapter ~~CHAPexpand) to specify that it
+is not to be expanded (unless you really do want to build a regular expression
+by expansion, of course).
+.nextp
+.index lookup||in domain list
+.index domain list||matching by lookup
+If a pattern starts with the name of a single-key lookup type followed by a
+semicolon (for example, `dbm;' or `lsearch;'), the remainder of the pattern
+must be a file name in a suitable format for the lookup type. For example, for
+`cdb;' it must be an absolute path:
+.display asis
+domains = cdb;/etc/mail/local_domains.cdb
+.endd
+The appropriate type of lookup is done on the file using the domain name as the
+key. In most cases, the data that is looked up is not used; Exim is interested
+only in whether or not the key is present in the file. However, when a lookup
+is used for the \domains\ option on a router
+or a \domains\ condition in an ACL statement, the data is preserved in the
+\$domain@_data$\ variable and can be referred to in other router options or
+other statements in the same ACL.
+.nextp
+Any of the single-key lookup type names may be preceded by `partial<<n>>-',
+where the <<n>> is optional, for example,
+.display asis
+domains = partial-dbm;/partial/domains
+.endd
+This causes partial matching logic to be invoked; a description of how this
+works is given in section ~~SECTpartiallookup.
+.nextp
+.index asterisk||in lookup type
+Any of the single-key lookup types may be followed by an asterisk. This causes
+a default lookup for a key consisting of a single asterisk to be done if the
+original lookup fails. This is not a useful feature when using a domain list to
+select particular domains (because any domain would match), but it might have
+value if the result of the lookup is being used via the \$domain@_data$\
+expansion variable.
+.nextp
+If the pattern starts with the name of a query-style lookup type followed by a
+semicolon (for example, `nisplus;' or `ldap;'), the remainder of the pattern
+must be an appropriate query for the lookup type, as described in chapter
+~~CHAPfdlookup. For example:
+.display asis
+hold_domains = mysql;select domain from holdlist \
+ where domain = '$domain';
+.endd
+In most cases, the data that is looked up is not used (so for an SQL query, for
+example, it doesn't matter what field you select). Exim is interested only in
+whether or not the query succeeds. However, when a lookup is used for the
+\domains\ option on a router, the data is preserved in the \$domain@_data$\
+variable and can be referred to in other options.
+.nextp
+.index domain list||matching literal domain name
+If none of the above cases apply, a caseless textual comparison is made between
+the pattern and the domain.
+.endp
+
+Here is an example that uses several different kinds of pattern:
+.display asis
+domainlist funny_domains = \
+ @ : \
+ lib.unseen.edu : \
+ *.foundation.fict.example : \
+ \N^[1-2]\d{3}\.fict\.example$\N : \
+ partial-dbm;/opt/data/penguin/book : \
+ nis;domains.byname : \
+ nisplus;[name=$domain,status=local],domains.org_dir
+.endd
+There are obvious processing trade-offs among the various matching modes. Using
+an asterisk is faster than a regular expression, and listing a few names
+explicitly probably is too. The use of a file or database lookup is expensive,
+but may be the only option if hundreds of names are required. Because the
+patterns are tested in order, it makes sense to put the most commonly matched
+patterns earlier.
+
+
+.section Host lists
+.rset SECThostlist "~~chapter.~~section"
+.index host list||patterns in
+.index list||host list
+Host lists are used to control what remote hosts are allowed to do. For
+example, some hosts may be allowed to use the local host as a relay, and some
+may be permitted to use the SMTP \\ETRN\\ command. Hosts can be identified in
+two different ways, by name or by IP address. In a host list, some types of
+pattern are matched to a host name, and some are matched to an IP address.
+You need to be particularly careful with this when single-key lookups are
+involved, to ensure that the right value is being used as the key.
+
+.section Special host list patterns
+.index empty item in hosts list
+.index host list||empty string in
+If a host list item is the empty string, it matches only when no remote host is
+involved. This is the case when a message is being received from a local
+process using SMTP on the standard input, that is, when a TCP/IP connection is
+not used.
+
+.index asterisk||in host list
+The special pattern `$*$' in a host list matches any host or no host. Neither
+the IP address nor the name is actually inspected.
+
+
+.section Host list patterns that match by IP address
+.rset SECThoslispatip "~~chapter.~~section"
+.index host list||matching IP addresses
+If an IPv4 host calls an IPv6 host and the call is accepted on an IPv6 socket,
+the incoming address actually appears in the IPv6 host as
+`@:@:$tt{ffff}:<<v4address>>'. When such an address is tested against a host
+list, it is converted into a traditional IPv4 address first. (Not all operating
+systems accept IPv4 calls on IPv6 sockets, as there have been some security
+concerns.)
+
+The following types of pattern in a host list check the remote host by
+inspecting its IP address:
+.numberpars $.
+If the pattern is a plain domain name (not a regular expression, not starting
+with $*$, not a lookup of any kind), Exim calls the operating system function
+to find the associated IP address(es). Exim uses the newer
+\*getipnodebyname()*\ function when available, otherwise \*gethostbyname()*\.
+This typically causes a forward DNS lookup of the name. The result is compared
+with the IP address of the subject host.
+
+.em
+If there is a temporary problem (such as a DNS timeout) with the host name
+lookup, a temporary error occurs. For example, if the list is being used in an
+ACL condition, the ACL gives a `defer' response, usually leading to a temporary
+SMTP error code. If no IP address can be found for the host name, what happens
+is described in section ~~SECTbehipnot below.
+.nem
+
+.nextp
+.index @@ in a host list
+If the pattern is `@@', the primary host name is substituted and used as a
+domain name, as just described.
+.nextp
+If the pattern is an IP address, it is matched against the IP address of the
+subject host. IPv4 addresses are given in the normal `dotted-quad' notation.
+IPv6 addresses can be given in colon-separated format, but the colons have to
+be doubled so as not to be taken as item separators when the default list
+separator is used. IPv6 addresses are recognized even when Exim is compiled
+without IPv6 support. This means that if they appear in a host list on an
+IPv4-only host, Exim will not treat them as host names. They are just addresses
+that can never match a client host.
+.nextp
+.index @@[] in a host list
+If the pattern is `@@[]', it matches the IP address of any IP interface on
+the local host. For example, if the local host is an IPv4 host with one
+interface address 10.45.23.56, these two ACL statements have the same effect:
+.display asis
+accept hosts = 127.0.0.1 : 10.45.23.56
+accept hosts = @[]
+.endd
+.nextp
+If the pattern is an IP address followed by a slash and a mask length (for
+example 10.11.42.0/24), it is matched against the IP address of the subject
+host under the given mask.
+This allows, an entire network of hosts to be included (or excluded) by a
+single item.
+.index CIDR notation
+The mask uses CIDR notation; it specifies the number of address bits that must
+match, starting from the most significant end of the address.
+
+\**Note**\: the mask is \*not*\ a count of addresses, nor is it the high number
+of a range of addresses. It is the number of bits in the network portion of the
+address. The above example specifies a 24-bit netmask, so it matches all 256
+addresses in the 10.11.42.0 network. An item such as
+.display asis
+192.168.23.236/31
+.endd
+matches just two addresses, 192.168.23.236 and 192.168.23.237. A mask value of
+32 for an IPv4 address is the same as no mask at all; just a single address
+matches.
+
+Here is another example which shows an IPv4 and an IPv6 network:
+.display asis
+recipient_unqualified_hosts = 192.168.0.0/16: \
+ 3ffe::ffff::836f::::/48
+.endd
+The doubling of list separator characters applies only when these items
+appear inline in a host list. It is not required when indirecting via a file.
+For example,
+.display asis
+recipient_unqualified_hosts = /opt/exim/unqualnets
+.endd
+could make use of a file containing
+.display asis
+172.16.0.0/12
+3ffe:ffff:836f::/48
+.endd
+to have exactly the same effect as the previous example. When listing IPv6
+addresses inline, it is usually more convenient to use the facility for
+changing separator characters. This list contains the same two networks:
+.display asis
+recipient_unqualified_hosts = <; 172.16.0.0/12; \
+ 3ffe:ffff:836f::/48
+.endd
+The separator is changed to semicolon by the leading `<;' at the start of the
+list.
+.endp
+
+
+.section Host list patterns for single-key lookups by host address
+.rset SECThoslispatsikey "~~chapter.~~section"
+.index host list||lookup of IP address
+When a host is to be identified by a single-key lookup of its complete IP
+address, the pattern takes this form:
+.display
+net-<<single-key-search-type>>;<<search-data>>
+.endd
+For example:
+.display asis
+hosts_lookup = net-cdb;/hosts-by-ip.db
+.endd
+The text form of the IP address of the subject host is used as the lookup key.
+IPv6 addresses are converted to an unabbreviated form, using lower case
+letters, with dots as separators because colon is the key terminator in
+\%lsearch%\ files. [Colons can in fact be used in keys in \%lsearch%\ files by
+quoting the keys, but this is a facility that was added later.] The data
+returned by the lookup is not used.
+
+.index IP address||masking
+.index host list||masked IP address
+Single-key lookups can also be performed using masked IP addresses, using
+patterns of this form:
+.display
+net<<number>>-<<single-key-search-type>>;<<search-data>>
+.endd
+For example:
+.display asis
+net24-dbm;/networks.db
+.endd
+The IP address of the subject host is masked using <<number>> as the mask
+length. A textual string is constructed from the masked value, followed by the
+mask, and this is used as the lookup key. For example, if the host's IP address
+is 192.168.34.6, the key that is looked up for the above example is
+`192.168.34.0/24'. IPv6 addresses are converted to a text value using lower
+case letters and dots as separators instead of the more usual colon, because
+colon is the key terminator in \%lsearch%\ files. Full, unabbreviated IPv6
+addresses are always used.
+
+\**Warning**\: Specifing \net32@-\ (for an IPv4 address) or \net128@-\ (for an
+IPv6 address) is not the same as specifing just \net@-\ without a number. In
+the former case the key strings include the mask value, whereas in the latter
+case the IP address is used on its own.
+
+
+.section Host list patterns that match by host name
+.rset SECThoslispatnam "~~chapter.~~section"
+.index host||lookup failures
+.index unknown host name
+.index host list||matching host name
+There are several types of pattern that require Exim to know the name of the
+remote host. These are either wildcard patterns or lookups by name. (If a
+complete hostname is given without any wildcarding, it is used to find an IP
+address to match against, as described in the section ~~SECThoslispatip above.)
+
+If the remote host name is not already known when Exim encounters one of these
+patterns, it has to be found from the IP address.
+.em
+Although many sites on the Internet are conscientious about maintaining reverse
+DNS data for their hosts, there are also many that do not do this.
+Consequently, a name cannot always be found, and this may lead to unwanted
+effects. Take care when configuring host lists with wildcarded name patterns.
+Consider what will happen if a name cannot be found.
+
+Because of the problems of determining host names from IP addresses, matching
+against host names is not as common as matching against IP addresses.
+
+By default, in order to find a host name, Exim first does a reverse DNS lookup;
+if no name is found in the DNS, the system function (\*gethostbyaddr()*\ or
+\*getipnodebyaddr()*\ if available) is tried. The order in which these lookups
+are done can be changed by setting the \host@_lookup@_order\ option.
+
+There are some options that control what happens if a host name cannot be
+found. These are described in section ~~SECTbehipnot below.
+.nem
+
+
+.index host||alias for
+.index alias for host
+As a result of aliasing, hosts may have more than one name. When processing any
+of the following types of pattern, all the host's names are checked:
+.numberpars $.
+.index asterisk||in host list
+If a pattern starts with `$*$' the remainder of the item must match the end of
+the host name. For example, \"*.b.c"\ matches all hosts whose names end in
+\*.b.c*\. This special simple form is provided because this is a very common
+requirement. Other kinds of wildcarding require the use of a regular
+expression.
+.nextp
+.index regular expressions||in host list
+.index host list||regular expression in
+If the item starts with `@^' it is taken to be a regular expression which is
+matched against the host name. For example,
+.display asis
+^(a|b)\.c\.d$
+.endd
+is a regular expression that matches either of the two hosts \*a.c.d*\ or
+\*b.c.d*\. When a regular expression is used in a host list, you must take care
+that backslash and dollar characters are not misinterpreted as part of the
+string expansion. The simplest way to do this is to use \"@\N"\ to mark that
+part of the string as non-expandable. For example:
+.display asis
+sender_unqualified_hosts = \N^(a|b)\.c\.d$\N : ....
+.endd
+.em
+\**Warning**\: If you want to match a complete host name, you must include the
+\"@$"\ terminating metacharacter in the regular expression, as in the above
+example. Without it, a match at the start of the host name is all that is
+required.
+.nem
+.endp
+
+
+.em
+.section Behaviour when an IP address or name cannot be found
+.rset SECTbehipnot "~~chapter.~~section"
+.index host||lookup failures
+While processing a host list, Exim may need to look up an IP address from a
+name (see section ~~SECThoslispatip), or it may need to look up a host name
+from an IP address (see section ~~SECThoslispatnam). In either case, the
+behaviour when it fails to find the information it is seeking is the same.
+
+.index \"+include@_unknown"\
+.index \"+ignore@_unknown"\
+By default, Exim behaves as if the host does not match the list. This may not
+always be what you want to happen. To change Exim's behaviour, the special
+items \"+include@_unknown"\ or \"+ignore@_unknown"\ may appear in the list (at
+top level -- they are not recognized in an indirected file).
+.numberpars $.
+If any item that follows \"+include@_unknown"\ requires information that
+cannot found, Exim behaves as if the host does match the list. For example,
+.display asis
+host_reject_connection = +include_unknown:*.enemy.ex
+.endd
+rejects connections from any host whose name matches \"*.enemy.ex"\, and also
+any hosts whose name it cannot find.
+.nextp
+If any item that follows \"+ignore@_unknown"\ requires information that cannot
+be found, Exim ignores that item and proceeds to the rest of the list. For
+example:
+.display asis
+accept hosts = +ignore_unknown : friend.example : \
+ 192.168.4.5
+.endd
+accepts from any host whose name is \*friend.example*\ and from 192.168.4.5,
+whether or not its host name can be found. Without \"+ignore@_unknown"\, if no
+name can be found for 192.168.4.5, it is rejected.
+.endp
+Both \"+include@_unknown"\ and \"+ignore@_unknown"\ may appear in the same
+list. The effect of each one lasts until the next, or until the end of the
+list.
+
+\**Note**\: This section applies to permanent lookup failures. It does \*not*\
+apply to temporary DNS errors. They always cause a defer action.
+.nem
+
+
+.section Host list patterns for single-key lookups by host name
+.rset SECThoslispatnamsk "~~chapter.~~section"
+.index host||lookup failures
+.index unknown host name
+.index host list||matching host name
+If a pattern is of the form
+.display
+<<single-key-search-type>>;<<search-data>>
+.endd
+for example
+.display asis
+dbm;/host/accept/list
+.endd
+a single-key lookup is performend, using the host name as its key. If the
+lookup succeeds, the host matches the item. The actual data that is looked up
+is not used.
+
+\**Reminder**\: With this kind of pattern, you must have host $it{names} as
+keys in the file, not IP addresses. If you want to do lookups based on IP
+addresses, you must precede the search type with `net-' (see section
+~~SECThoslispatsikey). There is, however, no reason why you could not use two
+items in the same list, one doing an address lookup and one doing a name
+lookup, both using the same file.
+
+
+.section Host list patterns for query-style lookups
+If a pattern is of the form
+.display
+<<query-style-search-type>>;<<query>>
+.endd
+the query is obeyed, and if it succeeds, the host matches the item. The actual
+data that is looked up is not used. The variables \$sender@_host@_address$\ and
+\$sender@_host@_name$\ can be used in the query. For example:
+.display asis
+hosts_lookup = pgsql;\
+ select ip from hostlist where ip='$sender_host_address'
+.endd
+The value of \$sender@_host@_address$\ for an IPv6 address uses colon
+separators. You can use the \sg\ expansion item to change this if you need to.
+If you want to use masked IP addresses in database queries, you can use the
+\mask\ expansion operator.
+
+If the query contains a reference to \$sender@_host@_name$\, Exim automatically
+looks up the host name if has not already done so. (See section
+~~SECThoslispatnam for comments on finding host names.)
+
+Historical note: prior to release 4.30, Exim would always attempt to find a
+host name before running the query, unless the search type was preceded by
+\"net-"\. This is no longer the case. For backwards compatibility, \"net-"\ is
+still recognized for query-style lookups, but its presence or absence has no
+effect. (Of course, for single-key lookups, \"net-"\ $it{is} important.)
+
+
+.section Mixing wildcarded host names and addresses in host lists
+.rset SECTmixwilhos "~~chapter.~~section"
+.index host list||mixing names and addresses in
+If you have name lookups or wildcarded host names and IP addresses in the same
+host list, you should normally put the IP addresses first. For example, in an
+ACL you could have:
+.display asis
+accept hosts = 10.9.8.7 : *.friend.example
+.endd
+The reason for this lies in the left-to-right way that Exim processes lists.
+It can test IP addresses without doing any DNS lookups, but when it reaches an
+item that requires a host name, it fails if it cannot find a host name to
+compare with the pattern. If the above list is given in the opposite order, the
+\accept\ statement fails for a host whose name cannot be found, even if its
+IP address is 10.9.8.7.
+
+If you really do want to do the name check first, and still recognize the IP
+address, you can rewrite the ACL like this:
+.display asis
+accept hosts = *.friend.example
+accept hosts = 10.9.8.7
+.endd
+If the first \accept\ fails, Exim goes on to try the second one. See chapter
+~~CHAPACL for details of ACLs.
+
+
+
+
+.section Address lists
+.index list||address list
+.index address list||empty item
+.index address list||patterns
+.rset SECTaddresslist "~~chapter.~~section"
+Address lists contain patterns that are matched against mail addresses. There
+is one special case to be considered: the sender address of a bounce message is
+always empty. You can test for this by providing an empty item in an address
+list. For example, you can set up a router to process bounce messages by
+using this option setting:
+.display asis
+senders = :
+.endd
+The presence of the colon creates an empty item. If you do not provide any
+data, the list is empty and matches nothing. The empty sender can also be
+detected by a regular expression that matches an empty string.
+
+The following kinds of pattern are supported in address lists:
+.numberpars $.
+.index regular expressions||in address list
+.index address list||regular expression in
+If (after expansion) a pattern starts with `@^', a regular expression match is
+done against the complete address, with the pattern as the regular expression.
+You must take care that backslash and dollar characters are not misinterpreted
+as part of the string expansion. The simplest way to do this is to use \"@\N"\
+to mark that part of the string as non-expandable. For example:
+.display asis
+deny senders = \N^\d{8}.+@spamhaus.example$\N : ...
+.endd
+The \"@\N"\ sequences are removed by the expansion, so the item does start
+with `@^' by the time it is being interpreted as an address pattern.
+.nextp
+.index @@@@ with single-key lookup
+.index address list||@@@@ lookup type
+.index address list||split local part and domain
+If a pattern starts with `@@@@' followed by a single-key lookup item
+(for example, \"@@@@lsearch;/some/file"\), the address that is being checked is
+split into a local part and a domain. The domain is looked up in the file. If
+it is not found, there is no match. If it is found, the data that is looked up
+from the file is treated as a colon-separated list of local part patterns, each
+of which is matched against the subject local part in turn.
+
+.index asterisk||in address list
+The lookup may be a partial one, and/or one involving a search for a default
+keyed by `$*$' (see section ~~SECTdefaultvaluelookups). The local part patterns
+that are looked up can be regular expressions or begin with `$*$', or even be
+further lookups. They may also be independently negated. For example, with
+.display asis
+deny senders = @@dbm;/etc/reject-by-domain
+.endd
+the data from which the DBM file is built could contain lines like
+.display asis
+baddomain.com: !postmaster : *
+.endd
+to reject all senders except \postmaster\ from that domain.
+.index local part||starting with !
+If a local part that actually begins with an exclamation mark is required, it
+has to be specified using a regular expression. In \%lsearch%\ files, an entry
+may be split over several lines by indenting the second and subsequent lines,
+but the separating colon must still be included at line breaks. White space
+surrounding the colons is ignored. For example:
+.display asis
+aol.com: spammer1 : spammer2 : ^[0-9]+$ :
+ spammer3 : spammer4
+.endd
+As in all colon-separated lists in Exim, a colon can be included in an item by
+doubling.
+
+If the last item in the list starts with a right angle-bracket, the remainder
+of the item is taken as a new key to look up in order to obtain a continuation
+list of local parts. The new key can be any sequence of characters. Thus one
+might have entries like
+.display asis
+aol.com: spammer1 : spammer 2 : >*
+xyz.com: spammer3 : >*
+*: ^\d{8}$
+.endd
+in a file that was searched with \@@@@dbm$*$\, to specify a match for 8-digit
+local parts for all domains, in addition to the specific local parts listed for
+each domain. Of course, using this feature costs another lookup each time a
+chain is followed, but the effort needed to maintain the data is reduced.
+.index loop||in lookups
+It is possible to construct loops using this facility, and in order to catch
+them, the chains may be no more than fifty items long.
+.nextp
+The @@@@<<lookup>> style of item can also be used with a query-style
+lookup, but in this case, the chaining facility is not available. The lookup
+can only return a single list of local parts.
+.nextp
+.index address list||lookup for complete address
+Complete addresses can be looked up by using a pattern that
+starts with a lookup type terminated by a semicolon, follwed by the data for
+the lookup.
+For example:
+.display asis
+deny senders = cdb;/etc/blocked.senders : \
+ mysql;select address from blocked where \
+ address='${quote_mysql:$sender_address}'
+.endd
+For a single-key lookup type, Exim uses the complete address as the key.
+Partial matching (section ~~SECTpartiallookup) cannot be used, and is ignored
+if specified, with an entry being written to the panic log.
+
+.index @*@@ with single-key lookup
+You can configure lookup defaults, as described in section
+~~SECTdefaultvaluelookups, but this is useful only for the `$*$@@' type of
+default. For example, with this lookup:
+.display asis
+accept senders = lsearch*@;/some/file
+.endd
+the file could contains lines like this:
+.display asis
+user1@domain1.example
+*@domain2.example
+.endd
+and for the sender address \*nimrod@@jaeger.example*\, the sequence of keys
+that are tried is:
+.display asis
+nimrod@jaeger.example
+*@jaeger.example
+*
+.endd
+\**Warning 1**\: Do not include a line keyed by `$*$' in the file, because that
+would mean that every address matches, thus rendering the test useless.
+
+\**Warning 2**\: Do not confuse these two kinds of item:
+.display asis
+deny recipients = dbm*@;/some/file
+deny recipients = *@dbm;/some/file
+.endd
+The first does a whole address lookup, with defaulting, as just described,
+because it starts with a lookup type. The second matches the local part and
+domain independently, as described in the next paragraph.
+.nextp
+If a pattern contains an @@ character, but is not a regular expression
+and does not begin with a lookup type
+as described above, the local part of the subject address is compared with the
+local part of the pattern, which may start with an asterisk. If the local parts
+match, the domain is checked in exactly the same way as for a pattern in a
+domain list. For example, the domain can be wildcarded, refer to a named list,
+or be a lookup:
+.display asis
+deny senders = *@*.spamming.site:\
+ *@+hostile_domains:\
+ bozo@partial-lsearch;/list/of/dodgy/sites:\
+.newline
+ *@dbm;/bad/domains.db
+.endd
+.index local part||starting with !
+.index address list||local part starting with !
+If a local part that begins with an exclamation mark is required, it has to be
+specified using a regular expression, because otherwise the exclamation mark is
+treated as a sign of negation.
+.nextp
+If a pattern is not one of the above syntax forms, that is, if a pattern which
+is not a regular expression or a lookup does not contain an @@ character, it is
+matched against the domain part of the subject address. The only two formats
+that are recognized this way are a literal domain, or a domain pattern that
+starts with $*$. In both these cases, the effect is the same as if \"*@@"\
+preceded the pattern.
+.endp
+
+\**Warning**\: there is an important difference between the address list items
+in these two examples:
+.display asis
+senders = +my_list
+senders = *@+my_list
+.endd
+In the first one, \"my@_list"\ is a named address list, whereas in the second
+example it is a named domain list.
+
+
+
+.section Case of letters in address lists
+.rset SECTcasletadd "~~chapter.~~section"
+.index case of local parts
+.index address list||case forcing
+.index case forcing in address lists
+Domains in email addresses are always handled caselessly, but for local parts
+case may be significant on some systems (see \caseful@_local@_part\ for how
+Exim deals with this when routing addresses). However, RFC 2505 ($it{Anti-Spam
+Recommendations for SMTP MTAs}) suggests that matching of addresses to blocking
+lists should be done in a case-independent manner. Since most address lists in
+Exim are used for this kind of control, Exim attempts to do this by default.
+
+The domain portion of an address is always lowercased before matching it to an
+address list. The local part is lowercased by default, and any string
+comparisons that take place are done caselessly. This means that the data in
+the address list itself, in files included as plain file names, and in any file
+that is looked up using the `@@@@' mechanism, can be in any case. However, the
+keys in files that are looked up by a search type other than \%lsearch%\ (which
+works caselessly) must be in lower case, because these lookups are not
+case-independent.
+
+.index \"+caseful"\
+To allow for the possibility of caseful address list matching, if an item in
+an address list is the string `+caseful', the original case of the local
+part is restored for any comparisons that follow, and string comparisons are no
+longer case-independent. This does not affect the domain, which remains in
+lower case. However, although independent matches on the domain alone are still
+performed caselessly, regular expressions that match against an entire address
+become case-sensitive after `+caseful' has been seen.
+
+
+.section Local part lists
+.rset SECTlocparlis "~~chapter.~~section"
+.index list||local part list
+.index local part||list
+Case-sensitivity in local part lists is handled in the same way as for address
+lists, as just described. The `+caseful' item can be used if required. In a
+setting of the \local@_parts\ option in a router with \caseful@_local@_part\
+set false, the subject is lowercased and the matching is initially
+case-insensitive. In this case, `+caseful' will restore case-sensitive matching
+in the local part list, but not elsewhere in the router. If
+\caseful@_local@_part\ is set true in a router, matching in the \local@_parts\
+option is case-sensitive from the start.
+
+If a local part list is indirected to a file (see section ~~SECTfilnamlis),
+comments are handled in the same way as address lists -- they are recognized
+only if the @# is preceded by white space or the start of the line.
+Otherwise, local part lists are matched in the same way as domain lists, except
+that the special items that refer to the local host (\"@@"\, \"@@[]"\,
+\"@@mx@_any"\, \"@@mx@_primary"\, and \"@@mx@_secondary"\) are not recognized.
+Refer to section ~~SECTdomainlist for details of the other available item
+types.
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter String expansions
+.set runningfoot "string expansions"
+.rset CHAPexpand ~~chapter
+.index expansion||of strings
+Many strings in Exim's run time configuration are expanded before use. Some of
+them are expanded every time they are used; others are expanded only once.
+
+When a string is being expanded it is copied verbatim from left to right except
+when a dollar or backslash character is encountered. A dollar specifies the
+start of a portion of the string which is interpreted and replaced as described
+below in section ~~SECTexpansionitems onwards. Backslash is used as an escape
+character, as described in the following section.
+
+
+.section Literal text in expanded strings
+.rset SECTlittext "~~chapter.~~section"
+.index expansion||including literal text
+An uninterpreted dollar can be included in an expanded string by putting a
+backslash in front of it. A backslash can be used to prevent any special
+character being treated specially in an expansion, including itself. If the
+string appears in quotes in the configuration file, two backslashes are
+required because the quotes themselves cause interpretation of backslashes when
+the string is read in (see section ~~SECTstrings).
+
+.index expansion||non-expandable substrings
+A portion of the string can specified as non-expandable by placing it between
+two occurrences of \"@\N"\. This is particularly useful for protecting regular
+expressions, which often contain backslashes and dollar signs. For example:
+.display asis
+deny senders = \N^\d{8}[a-z]@some\.site\.example$\N
+.endd
+On encountering the first \"@\N"\, the expander copies subsequent characters
+without interpretation until it reaches the next \"@\N"\ or the end of the
+string.
+
+
+.section Character escape sequences in expanded strings
+.index expansion||escape sequences
+A backslash followed by one of the letters `n', `r', or `t' in an expanded
+string is recognized as an escape sequence for the character newline, carriage
+return, or tab, respectively. A backslash followed by up to three octal digits
+is recognized as an octal encoding for a single character, and a backslash
+followed by `x' and up to two hexadecimal digits is a hexadecimal encoding.
+
+These escape sequences are also recognized in quoted strings when they are read
+in. Their interpretation in expansions as well is useful for unquoted strings,
+and for other cases such as looked-up strings that are then expanded.
+
+.section Testing string expansions
+.index expansion||testing
+.index testing||string expansion
+.index \-be-\ option
+Many expansions can be tested by calling Exim with the \-be-\ option. This takes
+the command arguments, or lines from the standard input if there are no
+arguments, runs them through the string expansion code, and writes the results
+to the standard output. Variables based on configuration values are set up, but
+since no message is being processed, variables such as \$local@_part$\ have no
+value. Nevertheless the \-be-\ option can be useful for checking out file and
+database lookups, and the use of expansion operators such as \sg\, \substr\ and
+\nhash\.
+
+Exim gives up its root privilege when it is called with the \-be-\ option, and
+instead runs under the uid and gid it was called with, to prevent users from
+using \-be-\ for reading files to which they do not have access.
+
+
+.section Expansion items
+.rset SECTexpansionitems "~~chapter.~~section"
+The following items are recognized in expanded strings. White space may be used
+between sub-items that are keywords or substrings enclosed in braces inside an
+outer set of braces, to improve readability. \**Warning**\: Within braces,
+white space is significant.
+
+.startitems
+
+.item "@$<<variable name>>#$rm{or}#@$@{<<variable name>>@}"
+.index expansion||variables
+Substitute the contents of the named variable, for example
+.display asis
+$local_part
+${domain}
+.endd
+The second form can be used to separate the name from subsequent alphanumeric
+characters. This form (using curly brackets) is available only for variables;
+it does $it{not} apply to message headers. The names of the variables are given
+in section ~~SECTexpvar below. If the name of a non-existent variable is given,
+the expansion fails.
+
+.item "@$@{<<op>>:<<string>>@}"
+.index expansion||operators
+The string is first itself expanded, and then the operation specified by <<op>>
+is applied to it. For example,
+.display asis
+${lc:$local_part}
+.endd
+The string starts with the first character after the colon, which may be
+leading white space. A list of operators is given in section ~~SECTexpop below.
+The operator notation is used for simple expansion items that have just one
+argument, because it reduces the number of braces and therefore makes the
+string easier to understand.
+
+.item "@$@{extract@{<<key>>@}@{<<string1>>@}@{<<string2>>@}@{<<string3>>@}@}"
+.index expansion||extracting substrings by key
+The key and <<string1>> are first expanded separately.
+Leading and trailing whitespace is removed from the key (but not from any of
+the strings).
+The key must not consist entirely of digits. The expanded <<string1>> must be
+of the form:
+.display
+<<key1>> = <<value1>> <<key2>> = <<value2>> ...
+.endd
+where the equals signs and spaces (but not both) are optional. If any of the
+values contain white space, they must be enclosed in double quotes, and any
+values that are enclosed in double quotes are subject to escape processing as
+described in section ~~SECTstrings. The expanded <<string1>> is searched for
+the value that corresponds to the key. The search is case-insensitive. If the
+key is found, <<string2>> is expanded, and replaces the whole item; otherwise
+<<string3>> is used. During the expansion of <<string2>> the variable \$value$\
+contains the value that has been extracted. Afterwards, it is restored to any
+previous value it might have had.
+
+If @{<<string3>>@} is omitted, the item is replaced by an empty string if the
+key is not found. If @{<<string2>>@} is also omitted, the value that was
+extracted is used. Thus, for example, these two expansions are identical, and
+yield `2001':
+.display
+@$@{extract@{gid@}{uid=1984 gid=2001@}@}
+@$@{extract@{gid@}{uid=1984 gid=2001@}@{@$value@}@}
+.endd
+Instead of @{<<string3>>@} the word `fail' (not in curly brackets) can appear,
+for example:
+.display
+@$@{extract@{Z@}@{A=... B=...@}@{@$value@} fail @}
+.endd
+@{<<string2>>@} must be present for `fail' to be recognized. When this syntax
+is used, if the extraction fails, the entire string expansion fails in a way
+that can be detected by the code in Exim which requested the expansion. This is
+called `forced expansion failure', and its consequences depend on the
+circumstances. In some cases it is no different from any other expansion
+failure, but in others a different action may be taken. Such variations are
+mentioned in the documentation of the option which is expanded.
+
+
+.item "@$@{extract@{<<number>>@}@{<<separators>>@}@{<<string1>>@}@{<<string2>>@}@{<<string3>>@}@}"
+.index expansion||extracting substrings by number
+The <<number>> argument must consist entirely of decimal digits,
+apart from leading and trailing whitespace, which is ignored.
+This is what distinguishes this form of \extract\ from the previous kind. It
+behaves in the same way, except that, instead of extracting a named field, it
+extracts from <<string1>> the field whose number is given as the first
+argument. You can use \$value$\ in <<string2>> or \"fail"\ instead of
+<<string3>> as before.
+
+The fields in the string are separated by any one of the characters in the
+separator string. These may include space or tab characters.
+The first field is numbered one. If the number is negative, the fields are
+counted from the end of the string, with the rightmost one numbered -1. If the
+number given is zero, the entire string is returned. If the modulus of the
+number is greater than the number of fields in the string, the result is the
+expansion of <<string3>>, or the empty string if <<string3>> is not provided.
+For example:
+.display asis
+${extract{2}{:}{x:42:99:& Mailer::/bin/bash}}
+.endd
+yields `42', and
+.display asis
+${extract{-4}{:}{x:42:99:& Mailer::/bin/bash}}
+.endd
+yields `99'. Two successive separators mean that the field between them is
+empty (for example, the fifth field above).
+
+
+.item "@$@{hash@{<<string1>>@}@{<<string2>>@}@{<<string3>>@}@}"
+.index hash function||textual
+.index expansion||textual hash
+This is a textual hashing function, and was the first to be implemented in
+early versions of Exim. In current releases, there are other hashing functions
+(numeric, MD5, and SHA-1), which are described below.
+
+The first two strings, after expansion, must be numbers. Call them <<m>> and
+<<n>>. If you are using fixed values for these numbers, that is, if <<string1>>
+and <<string2>> do not change when they are expanded, you can use the
+simpler operator notation that avoids some of the braces:
+.display
+@$@{hash@_<<n>>@_<<m>>:<<string>>@}
+.endd
+The second number is optional (in both notations).
+
+If <<n>> is greater than or equal to the length of the string, the expansion
+item returns the string. Otherwise it computes a new string of length <<n>> by
+applying a hashing function to the string. The new string consists of
+characters taken from the first <<m>> characters of the string
+.display asis
+abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQWRSTUVWXYZ0123456789
+.endd
+If <<m>> is not present the value 26 is used, so that only lower case
+letters appear. For example:
+.display
+@$@{hash@{3@}@{monty@}@} $rm{yields} \"jmg"\
+@$@{hash@{5@}@{monty@}@} $rm{yields} \"monty"\
+@$@{hash@{4@}@{62@}@{monty python@}@} $rm{yields} \"fbWx"\
+.endd
+
+
+.item "@$header@_<<header name>>:#$rm{or}#@$h@_<<header name>>:"
+.item "@$bheader@_<<header name>>:#$rm{or}#@$bh@_<<header name>>:"
+.item "@$rheader@_<<header name>>:#$rm{or}#@$rh@_<<header name>>:"
+.index expansion||header insertion
+.index \$header@_$\
+.index \$bheader@_$\
+.index \$rheader@_$\
+.index header lines||in expansion strings
+.index header lines||character sets
+.index header lines||decoding
+Substitute the contents of the named message header line, for example
+.display asis
+$header_reply-to:
+.endd
+The newline that terminates a header line is not included in the expansion, but
+internal newlines (caused by splitting the header line over several physical
+lines) may be present.
+
+The difference between \rheader\, \bheader\, and \header\ is in the way the
+data in the header line is interpreted.
+.numberpars $.
+\rheader\ gives the original `raw' content of the header line, with no
+processing at all, and without the removal of leading and trailing whitespace.
+.nextp
+.index base64 encoding||in header lines
+\bheader\ removes leading and trailing whitespace, and then decodes base64 or
+quoted-printable MIME `words' within the header text, but does no character
+set translation. If decoding of what looks superficially like a MIME `word'
+fails, the raw string is returned.
+.index binary zero||in header line
+If decoding produces a binary zero character, it is replaced by a question mark
+-- this is what Exim does for binary zeros that are actually received in header
+lines.
+.nextp
+\header\ tries to translate the string as decoded by \bheader\ to a standard
+character set. This is an attempt to produce the same string as would be
+displayed on a user's MUA. If translation fails, the \bheader\ string is
+returned. Translation is attempted only on operating systems that support the
+\*iconv()*\ function. This is indicated by the compile-time macro
+\\HAVE@_ICONV\\ in a system Makefile or in \(Local/Makefile)\.
+.endp
+
+In a filter file, the target character set for \header\ can be specified by a
+command of the following form:
+.display asis
+headers charset "UTF-8"
+.endd
+This command affects all references to \$h@_$\ (or \$header@_$\) expansions in
+subsequently obeyed filter commands. In the absence of this command, the target
+character set in a filter is taken from the setting of the \headers@_charset\
+option in the runtime configuration. The value of this option defaults to the
+value of \\HEADERS@_CHARSET\\ in \(Local/Makefile)\. The ultimate default is
+ISO-8859-1.
+
+Header names follow the syntax of RFC 2822, which states that they may contain
+any printing characters except space and colon. Consequently, curly brackets
+$it{do not} terminate header names, and should not be used to enclose them as
+if they were variables. Attempting to do so causes a syntax error.
+
+Only header lines that are common to all copies of a message are visible to
+this mechanism. These are the original header lines that are received with the
+message, and any that are added by
+an ACL \warn\ statement or by
+a system filter. Header lines that are added to a particular copy of a message
+by a router or transport are not accessible.
+
+For incoming SMTP messages, no header lines are visible in ACLs that are obeyed
+before the \\DATA\\ ACL, because the header structure is not set up until the
+message is received. Header lines that are added by \warn\ statements in a
+\\RCPT\\ ACL (for example) are saved until the message's incoming header lines
+are available, at which point they are added. When a \\DATA\\ ACL is running,
+however, header lines added by earlier ACLs are visible.
+
+Upper case and lower case letters are synonymous in header names. If the
+following character is white space, the terminating colon may be omitted, but
+this is not recommended, because you may then forget it when it is needed. When
+white space terminates the header name, it is included in the expanded string.
+If the message does not contain the given header, the expansion item is
+replaced by an empty string. (See the \def\ condition in section ~~SECTexpcond
+for a means of testing for the existence of a header.)
+
+If there is more than one header with the same name, they are all concatenated
+to form the substitution string, up to a maximum length of 64K. A newline
+character is inserted between each line.
+For the \header\ expansion, for those headers that contain lists of addresses,
+a comma is also inserted at the junctions between lines. This does not happen
+for the \rheader\ expansion.
+
+
+
+.item "@$@{hmac@{<<hashname>>@}@{<<secret>>@}@{<<string>>@}@}"
+.index expansion||hmac hashing
+This function uses cryptographic hashing (either MD5 or SHA-1) to convert a
+shared secret and some text into a message authentication code, as specified in
+RFC 2104.
+This differs from \"@$@{md5:secret@_text...@}"\ or
+\"@$@{sha1:secret@_text...@}"\ in that the hmac step adds a signature to the
+cryptographic hash, allowing for authentication that is not possible with MD5
+or SHA-1 alone.
+The hash name must expand to either \"md5"\ or \"sha1"\ at present. For
+example:
+.display asis
+${hmac{md5}{somesecret}{$primary_hostname $tod_log}}
+.endd
+For the hostname \*mail.example.com*\ and time 2002-10-17 11:30:59, this
+produces:
+.display asis
+dd97e3ba5d1a61b5006108f8c8252953
+.endd
+As an example of how this might be used, you might put in the main part of
+an Exim configuration:
+.display asis
+SPAMSCAN_SECRET=cohgheeLei2thahw
+.endd
+In a router or a transport you could then have:
+.display asis
+headers_add = \
+ X-Spam-Scanned: ${primary_hostname} ${message_id} \
+ ${hmac{md5}{SPAMSCAN_SECRET}\
+ {${primary_hostname},${message_id},$h_message-id:}}
+.endd
+Then given a message, you can check where it was scanned by looking at the
+::X-Spam-Scanned:: header line. If you know the secret, you can check that this
+header line is authentic by recomputing the authentication code from the host
+name, message ID and the ::Message-id:: header line. This can be done using
+Exim's \-be-\ option, or by other means, for example by using the
+\*hmac@_md5@_hex()*\ function in Perl.
+
+
+
+.item "@${if <<condition>> @{<<string1>>@}@{<<string2>>@}@}"
+.index expansion||conditional
+If <<condition>> is true, <<string1>> is expanded and replaces the whole item;
+otherwise <<string2>> is used. For example,
+.display asis
+${if eq {$local_part}{postmaster} {yes}{no} }
+.endd
+The second string need not be present; if it is not and the condition is not
+true, the item is replaced with nothing. Alternatively, the word `fail' may be
+present instead of the second string (without any curly brackets). In this
+case, the expansion is forced to fail if the condition is not true. The
+available conditions are described in section ~~SECTexpcond below.
+
+
+.item "@$@{length@{<<string1>>@}@{<<string2>>@}@}"
+.index expansion||string truncation
+The \length\ item is used to extract the initial portion of a string. Both
+strings are expanded, and the first one must yield a number, <<n>>, say. If you
+are using a fixed value for the number, that is, if <<string1>> does not change
+when expanded, you can use the simpler operator notation that avoids some of
+the braces:
+.display
+@$@{length@_<<n>>:<<string>>@}
+.endd
+The result of this item is either the first <<n>> characters or the whole
+of <<string2>>, whichever is the shorter. Do not confuse \length\ with
+\strlen\, which gives the length of a string.
+
+
+.item "@${lookup@{<<key>>@} <<search type>> @{<<file>>@} @{<<string1>>@} @{<<string2>>@}@}"
+.item "@${lookup <<search type>> @{<<query>>@} @{<<string1>>@} @{<<string2>>@}@}"
+.index expansion||lookup in
+.index file||lookup
+.index lookup||in expanded string
+These items specify data lookups in files and databases, as discussed in
+chapter ~~CHAPfdlookup. The first form is used for single-key lookups, and the
+second is used for query-style lookups. The <<key>>, <<file>>, and <<query>>
+strings are expanded before use.
+
+If there is any white space in a lookup item which is part of a filter command,
+a retry or rewrite rule, a routing rule for the \%manualroute%\ router, or any
+other place where white space is significant, the lookup item must be enclosed
+in double quotes. The use of data lookups in users' filter files may be locked
+out by the system administrator.
+
+.index \$value$\
+If the lookup succeeds, <<string1>> is expanded and replaces the entire item.
+During its expansion, the variable \$value$\ contains the data returned by the
+lookup. Afterwards it reverts to the value it had previously (at the outer
+level it is empty). If the lookup fails, <<string2>> is expanded and replaces
+the entire item. If @{<<string2>>@} is omitted, the replacement is null on
+failure. Alternatively, <<string2>> can itself be a nested lookup, thus
+providing a mechanism for looking up a default value when the original lookup
+fails.
+
+If a nested lookup is used as part of <<string1>>, \$value$\ contains the data
+for the outer lookup while the parameters of the second lookup are expanded,
+and also while <<string2>> of the second lookup is expanded, should the second
+lookup fail.
+
+Instead of @{<<string2>>@} the word `fail' can appear, and in this case, if the
+lookup fails, the entire expansion is forced to fail. If both @{<<string1>>@}
+and @{<<string2>>@} are omitted, the result is the looked up value in the case
+of a successful lookup, and nothing in the case of failure.
+
+For single-key lookups, the string `partial' is permitted to precede the
+search type in order to do partial matching, and $*$ or $*$@@ may follow a
+search type to request default lookups if the key does not match (see sections
+~~SECTdefaultvaluelookups and ~~SECTpartiallookup for details).
+
+.index numerical variables (\$1$\, \$2$\, etc)||in lookup expansion
+If a partial search is used, the variables \$1$\ and \$2$\ contain the wild
+and non-wild parts of the key during the expansion of the replacement text.
+They return to their previous values at the end of the lookup item.
+
+This example looks up the postmaster alias in the conventional alias file:
+.display asis
+${lookup {postmaster} lsearch {/etc/aliases} {$value}}
+.endd
+This example uses NIS+ to look up the full name of the user corresponding to
+the local part of an address, forcing the expansion to fail if it is not found:
+.display asis
+${lookup nisplus {[name=$local_part],passwd.org_dir:gcos} \
+ {$value}fail}
+.endd
+
+
+.item "@$@{nhash@{<<string1>>@}@{<<string2>>@}@{<<string3>>@}@}"
+.index expansion||numeric hash
+.index hash function||numeric
+The three strings are expanded; the first two must yield numbers. Call them
+<<n>> and <<m>>. If you are using fixed values for these numbers, that is, if
+<<string1>> and <<string2>> do not change when they are expanded, you can use
+the simpler operator notation that avoids some of the braces:
+.display
+@$@{nhash@_<<n>>@_<<m>>:<<string>>@}
+.endd
+The second number is optional (in both notations). If there is only one number,
+the result is a number in the range 0--<<n>>-1. Otherwise, the string is
+processed by a div/mod hash function that returns two numbers, separated by a
+slash, in the ranges 0 to <<n>>-1 and 0 to <<m>>-1, respectively. For example,
+.display asis
+${nhash{8}{64}{supercalifragilisticexpialidocious}}
+.endd
+returns the string `6/33'.
+
+
+
+.item "@$@{perl@{<<subroutine>>@}@{<<arg>>@}@{<<arg>>@}...@}"
+.index Perl||use in expanded string
+.index expansion||calling Perl from
+This item is available only if Exim has been built to include an embedded Perl
+interpreter. The subroutine name and the arguments are first separately
+expanded, and then the Perl subroutine is called with those arguments. No
+additional arguments need be given; the maximum number permitted, including the
+name of the subroutine, is nine.
+
+The return value of the subroutine is inserted into the expanded string, unless
+the return value is \undef\. In that case, the expansion fails in the same way
+as an explicit `fail' on a lookup item.
+The return value is a scalar. Whatever you return is evaluated in a scalar
+context. For example, if you return the name of a Perl vector, the
+return value is the size of the vector, not its contents.
+
+If the subroutine exits by calling Perl's \die\ function, the expansion fails
+with the error message that was passed to \die\. More details of the embedded
+Perl facility are given in chapter ~~CHAPperl.
+
+The \%redirect%\ router has an option called \forbid@_filter@_perl\ which locks
+out the use of this expansion item in filter files.
+
+
+.item "@$@{readfile@{<<file name>>@}@{<<eol string>>@}@}"
+.index expansion||inserting an entire file
+.index file||inserting into expansion
+The file name and end-of-line string are first expanded separately. The file is
+then read, and its contents replace the entire item. All newline characters in
+the file are replaced by the end-of-line string if it is present. Otherwise,
+newlines are left in the string.
+String expansion is not applied to the contents of the file. If you want this,
+you must wrap the item in an \expand\ operator. If the file cannot be read, the
+string expansion fails.
+
+The \%redirect%\ router has an option called \forbid@_filter@_readfile\ which
+locks out the use of this expansion item in filter files.
+
+
+
+.item "@$@{readsocket@{<<name>>@}@{<<request>>@}@{<<timeout>>@}@{<<eol string>>@}@{<<fail string>>@}@}"
+.index expansion||inserting from a socket
+.index socket, use of in expansion
+This item inserts data that is read from a Unix domain socket into the expanded
+string. The minimal way of using it uses just two arguments:
+.display asis
+${readsocket{/socket/name}{request string}}
+.endd
+Exim connects to the socket, writes the request string (unless it is an
+empty string) and reads from the socket until an end-of-file is read. A timeout
+of 5 seconds is applied. Additional, optional arguments extend what can be
+done. Firstly, you can vary the timeout. For example:
+.display asis
+${readsocket{/socket/name}{request-string}{3s}}
+.endd
+A fourth argument allows you to change any newlines that are in the data
+that is read, in the same way as for \readfile\ (see above). This example turns
+them into spaces:
+.display asis
+${readsocket{/socket/name}{request-string}{3s}{ }}
+.endd
+As with all expansions, the substrings are expanded before the processing
+happens. Errors in these sub-expansions cause the expansion to fail. In
+addition, the following errors can occur:
+.numberpars $.
+Failure to create a socket file descriptor;
+.nextp
+Failure to connect the socket;
+.nextp
+Failure to write the request-string;
+.nextp
+Timeout on reading from the socket.
+.endp
+By default, any of these errors causes the expansion to fail. However, if
+you supply a fifth substring, it is expanded and used when any of the above
+errors occurs. For example:
+.display asis
+${readsocket{/socket/name}{request-string}{3s}{\n}\
+ {socket failure}}
+.endd
+You can test for the existence of the socket by wrapping this expansion in
+\"@$@{if exists"\, but there is a race condition between that test and the
+actual opening of the socket, so it is safer to use the fifth argument if you
+want to be absolutely sure of avoiding an expansion error for a non-existent
+socket.
+
+The \%redirect%\ router has an option called \forbid@_filter@_readsocket\ which
+locks out the use of this expansion item in filter files.
+
+.item "@$rheader@_<<header name>>:#$rm{or}#@$rh@_<<header name>>:"
+This item inserts `raw' header lines. It is described with the \header\
+expansion item above.
+
+
+
+.item "@$@{run@{<<command>> <<args>>@}@{<<string1>>@}@{<<string2>>@}@}"
+.index expansion||running a command
+The command and its arguments are first expanded separately, and then the
+command is run in a separate process, but under the same uid and gid. As in
+other command executions from Exim, a shell is not used by default. If you want
+a shell, you must explicitly code it.
+.index return code||from \run\ expansion
+If the command succeeds (gives a zero return code) <<string1>> is expanded and
+replaces the entire item; during this expansion, the standard output from the
+command is in the variable \$value$\. If the command fails, <<string2>>, if
+present, is expanded. If it is absent, the result is empty. Alternatively,
+<<string2>> can be the word `fail' (not in braces) to force expansion failure
+if the command does not succeed. If both strings are omitted, the result is the
+standard output on success, and nothing on failure.
+
+The return code from the command is put in the variable \$runrc$\, and this
+remains set afterwards, so in a filter file you can do things like this:
+.display asis
+if "${run{x y z}{}}$runrc" is 1 then ...
+ elif $runrc is 2 then ...
+ ...
+endif
+.endd
+If execution of the command fails (for example, the command does not exist),
+the return code is 127 -- the same code that shells use for non-existent
+commands.
+
+\**Warning**\: In a router or transport, you cannot assume the order in which
+option values are expanded, except for those pre-conditions whose order of
+testing is documented. Therefore, you cannot reliably expect to set \$runrc$\
+by the expansion of one option, and use it in another.
+
+The \%redirect%\ router has an option called \forbid@_filter@_run\ which locks
+out the use of this expansion item in filter files.
+
+
+.item "@$@{sg@{<<subject>>@}@{<<regex>>@}@{<<replacement>>@}@}"
+.index expansion||string substitution
+This item works like Perl's substitution operator (s) with the global (/g)
+option; hence its name. However, unlike the Perl equivalent, Exim does not
+modify the subject string; instead it returns the modified string for insertion
+into the overall expansion. The item takes three arguments: the subject string,
+a regular expression, and a substitution string. For example
+.display asis
+${sg{abcdefabcdef}{abc}{xyz}}
+.endd
+yields `xyzdefxyzdef'. Because all three arguments are expanded before use, if
+any @$ or @\ characters are required in the regular expression or in the
+substitution string, they have to be escaped. For example
+.display asis
+${sg{abcdef}{^(...)(...)\$}{\$2\$1}}
+.endd
+yields `defabc', and
+.display asis
+${sg{1=A 4=D 3=C}{\N(\d+)=\N}{K\$1=}}
+.endd
+yields `K1=A K4=D K3=C'.
+Note the use of \"@\N"\ to protect the contents of the regular expression from
+string expansion.
+
+
+
+.item "@$@{substr@{<<string1>>@}@{<<string2>>@}@{<<string3>>@}@}"
+.index \substr\
+.index substring extraction
+.index expansion||substring extraction
+The three strings are expanded; the first two must yield numbers. Call them
+<<n>> and <<m>>. If you are using fixed values for these numbers, that is, if
+<<string1>> and <<string2>> do not change when they are expanded, you can use
+the simpler operator notation that avoids some of the braces:
+.display
+@$@{substr@_<<n>>@_<<m>>:<<string>>@}
+.endd
+The second number is optional (in both notations).
+
+The \substr\ item can be used to extract more general substrings than \length\.
+The first number, <<n>>, is a starting offset, and <<m>> is the length
+required. For example
+.display asis
+${substr{3}{2}{$local_part}}
+.endd
+If the starting offset is greater than the string length the result is the null
+string; if the length plus starting offset is greater than the string length,
+the result is the right-hand part of the string, starting from the given
+offset. The first character in the string has offset zero.
+
+The \substr\ expansion item can take negative offset values to count
+from the right-hand end of its operand. The last character is offset -1, the
+second-last is offset -2, and so on. Thus, for example,
+.display asis
+${substr{-5}{2}{1234567}}
+.endd
+yields `34'. If the absolute value of a negative offset is greater than the
+length of the string, the substring starts at the beginning of the string, and
+the length is reduced by the amount of overshoot. Thus, for example,
+.display asis
+${substr{-5}{2}{12}}
+.endd
+yields an empty string, but
+.display asis
+${substr{-3}{2}{12}}
+.endd
+yields `1'.
+
+If the second number is omitted from \substr\, the remainder of the string is
+taken if the offset was positive. If it was negative, all characters in the
+string preceding the offset point are taken. For example, an offset of -1 and
+no length yields all but the last character of the string.
+
+
+
+.item "@$@{tr@{<<subject>>@}@{<<characters>>@}@{<<replacements>>@}@}"
+.index expansion||character translation
+This item does single-character translation on its subject string. The second
+argument is a list of characters to be translated in the subject string. Each
+matching character is replaced by the corresponding character from the
+replacement list. For example
+.display asis
+${tr{abcdea}{ac}{13}}
+.endd
+yields `1b3de1'. If there are duplicates in the second character string, the
+last occurrence is used. If the third string is shorter than the second, its
+last character is replicated. However, if it is empty, no translation takes
+place.
+
+.enditems
+
+
+.section Expansion operators
+.rset SECTexpop "~~chapter.~~section"
+.index expansion||operators
+For expansion items that perform transformations on a single argument string,
+the `operator' notation is used because it is simpler and uses fewer braces.
+The substring is first expanded before the operation is applied to it. The
+following operations can be performed:
+
+.startitems
+
+.item "@$@{address:<<string>>@}"
+.index expansion||RFC 2822 address handling
+The string is interpreted as an RFC 2822 address, as it might appear in a
+header line, and the effective address is extracted from it. If the string does
+not parse successfully, the result is empty.
+
+
+.item "@$@{base62:<<digits>>@}"
+.index base62
+.index expansion||conversion to base 62
+The string must consist entirely of decimal digits. The number is converted to
+base 62 (sic) and output as a string of six characters, including leading
+zeros. \**Note**\: Just to be absolutely clear: this is \*not*\ base64
+encoding.
+
+.em
+.item "@$@{base62d:<<base-62 digits>>@}"
+.index base62
+.index expansion||conversion to base 62
+The string must consist entirely of base-62 digits. The number is converted to
+decimal and output as a string.
+.nem
+
+
+.item "@$@{domain:<<string>>@}"
+.index domain||extraction
+.index expansion||domain extraction
+The string is interpreted as an RFC 2822 address and the domain is extracted
+from it. If the string does not parse successfully, the result is empty.
+
+
+.item "@$@{escape:<<string>>@}"
+.index expansion||escaping non-printing characters
+If the string contains any non-printing characters, they are converted to
+escape sequences starting with a backslash. Whether characters with the most
+significant bit set (so-called `8-bit characters') count as printing or not is
+controlled by the \print@_topbitchars\ option.
+
+
+.em
+.item "@$@{eval:<<string>>@}"
+.item "@$@{eval10:<<string>>@}"
+.index expansion||expression evaluation
+.index expansion||arithmetic expression
+These items supports simple arithmetic in expansion strings. The string (after
+expansion) must be a conventional arithmetic expression, but it is limited to
+the four basic operators (plus, minus, times, divide) and parentheses. All
+operations are carried out using integer arithmetic. Plus and minus have a
+lower priority than times and divide; operators with the same priority are
+evaluated from left to right.
+
+For \eval\, numbers may be decimal, octal (starting with `0') or hexadecimal
+(starting with `0x'). For \eval10\, all numbers are taken as decimal, even if
+they start with a leading zero. This can be useful when processing numbers
+extracted from dates or times, which often do have leading zeros.
+.nem
+
+A number may be followed by `K' or `M' to multiply it by 1024 or 1024$*$1024,
+respectively. Negative numbers are supported. The result of the computation is
+a decimal representation of the answer (without `K' or `M'). For example:
+.display
+ @$@{eval:1+1@} $rm{yields} 2
+ @$@{eval:1+2*3@} $rm{yields} 7
+ @$@{eval:(1+2)*3@} $rm{yields} 9
+.endd
+As a more realistic example, in an ACL you might have
+.display asis
+deny message = Too many bad recipients
+ condition = \
+ ${if and { \
+ {>{$rcpt_count}{10}} \
+ { \
+ < \
+ {$recipients_count} \
+ {${eval:$rcpt_count/2}} \
+ } \
+ }{yes}{no}}
+.endd
+The condition is true if there have been more than 10 \\RCPT\\ commands and
+fewer than half of them have resulted in a valid recipient.
+
+
+.item "@$@{expand:<<string>>@}"
+.index expansion||re-expansion of substring
+The \expand\ operator causes a string to be expanded for a second time. For
+example,
+.display asis
+${expand:${lookup{$domain}dbm{/some/file}{$value}}}
+.endd
+first looks up a string in a file while expanding the operand for \expand\, and
+then re-expands what it has found.
+
+
+.item "@$@{from@_utf8:<<string>>@}"
+.index Unicode
+.index UTF-8||conversion from
+.index expansion||UTF-8 conversion
+The world is slowly moving towards Unicode, although there are no standards for
+email yet. However, other applications (including some databases) are starting
+to store data in Unicode, using UTF-8 encoding. This operator converts from a
+UTF-8 string to an ISO-8859-1 string. UTF-8 code values greater than 255 are
+converted to underscores. The input must be a valid UTF-8 string. If it is not,
+the result is an undefined sequence of bytes.
+
+Unicode code points with values less than 256 are compatible with ASCII and
+ISO-8859-1 (also known as Latin-1).
+For example, character 169 is the copyright symbol in both cases, though the
+way it is encoded is different. In UTF-8, more than one byte is needed for
+characters with code values greater than 127, whereas ISO-8859-1 is a
+single-byte encoding (but thereby limited to 256 characters). This makes
+translation from UTF-8 to ISO-8859-1 straightforward.
+
+
+.item "@$@{hash@_<<n>>@_<<m>>:<<string>>@}"
+.index hash function||textual
+.index expansion||textual hash
+The \hash\ operator is a simpler interface to the hashing function that can be
+used when the two parameters are fixed numbers (as opposed to strings that
+change when expanded). The effect is the same as
+.display
+@$@{hash@{<<n>>@}@{<<m>>@}@{<<string>>@}@}
+.endd
+See the description of the general \hash\ item above for details. The
+abbreviation \h\ can be used when \hash\ is used as an operator.
+
+
+
+.item "@$@{hex2b64:<<hexstring>>@}"
+.index base64 encoding||conversion from hex
+.index expansion||hex to base64
+This operator converts a hex string into one that is base64 encoded. This can
+be useful for processing the output of the MD5 and SHA-1 hashing functions.
+
+
+.item "@$@{lc:<<string>>@}"
+.index case forcing in strings
+.index string||case forcing
+.index lower casing
+.index expansion||case forcing
+This forces the letters in the string into lower-case, for example:
+.display asis
+${lc:$local_part}
+.endd
+
+
+.item "@$@{length@_<<number>>:<<string>>@}"
+.index expansion||string truncation
+The \length\ operator is a simpler interface to the \length\ function that can
+be used when the parameter is a fixed number (as opposed to a string that
+changes when expanded). The effect is the same as
+.display
+@$@{length@{<<number>>@}@{<<string>>@}@}
+.endd
+See the description of the general \length\ item above for details. Note that
+\length\ is not the same as \strlen\. The abbreviation \l\ can be used when
+\length\ is used as an operator.
+
+
+.item "@$@{local@_part:<<string>>@}"
+.index expansion||local part extraction
+The string is interpreted as an RFC 2822 address and the local part is
+extracted from it. If the string does not parse successfully, the result is
+empty.
+
+
+.item "@$@{mask:<<IP address>>/<<bit count>>@}"
+.index masked IP address
+.index IP address||masking
+.index CIDR notation
+.index expansion||IP address masking
+If the form of the string to be operated on is not an IP address followed by a
+slash and an integer (that is, a network address in CIDR notation), the
+expansion fails. Otherwise, this operator converts the IP address to binary,
+masks off the least significant bits according to the bit count, and converts
+the result back to text, with mask appended. For example,
+.display asis
+${mask:10.111.131.206/28}
+.endd
+returns the string `10.111.131.192/28'. Since this operation is expected to be
+mostly used for looking up masked addresses in files, the result for an IPv6
+address uses dots to separate components instead of colons, because colon
+terminates a key string in lsearch files. So, for example,
+.display asis
+${mask:3ffe:ffff:836f:0a00:000a:0800:200a:c031/99}
+.endd
+returns the string
+.display asis
+3ffe.ffff.836f.0a00.000a.0800.2000.0000/99
+.endd
+Letters in IPv6 addresses are always output in lower case.
+
+
+.item "@$@{md5:<<string>>@}"
+.index MD5 hash
+.index expansion||MD5 hash
+The \md5\ operator computes the MD5 hash value of the string, and returns it as
+a 32-digit hexadecimal number,
+in which any letters are in lower case.
+
+
+.item "@$@{nhash@_<<n>>@_<<m>>:<<string>>@}"
+.index expansion||numeric hash
+.index hash function||numeric
+The \nhash\ operator is a simpler interface to the numeric hashing function
+that can be used when the two parameters are fixed numbers (as opposed to
+strings that change when expanded). The effect is the same as
+.display
+@$@{nhash@{<<n>>@}@{<<m>>@}@{<<string>>@}@}
+.endd
+See the description of the general \nhash\ item above for details.
+
+
+.item "@$@{quote:<<string>>@}"
+.index quoting||in string expansions
+.index expansion||quoting
+The \quote\ operator puts its argument into double quotes if it
+is an empty string or
+contains anything other than letters, digits, underscores, dots, and hyphens.
+Any occurrences of double quotes and backslashes are escaped with a backslash.
+Newlines and carriage returns are converted to \"@\n"\ and \"@\r"\,
+respectively For example,
+.display asis
+${quote:ab"*"cd}
+.endd
+becomes
+.display asis
+"ab\"*\"cd"
+.endd
+The place where this is useful is when the argument is a substitution from a
+variable or a message header.
+
+.item "@$@{quote@_local@_part:<<string>>@}"
+This operator is like \quote\, except that it quotes the string only if
+required to do so by the rules of RFC 2822 for quoting local parts. For
+example, a plus sign would not cause quoting (but it would for \quote\).
+If you are creating a new email address from the contents of \$local@_part$\
+(or any other unknown data), you should always use this operator.
+
+
+.item "@$@{quote@_<<lookup-type>>:<<string>>@}"
+.index quoting||lookup-specific
+This operator applies lookup-specific quoting rules to the string. Each
+query-style lookup type has its own quoting rules which are described with
+the lookups in chapter ~~CHAPfdlookup. For example,
+.display asis
+${quote_ldap:two * two}
+.endd
+returns
+.display asis
+two%20%5C2A%20two
+.endd
+For single-key lookup types, no quoting is ever necessary and this operator
+yields an unchanged string.
+
+
+.item "@$@{rxquote:<<string>>@}"
+.index quoting||in regular expressions
+.index regular expressions||quoting
+The \rxquote\ operator inserts a backslash before any non-alphanumeric
+characters in its argument. This is useful when substituting the values of
+variables or headers inside regular expressions.
+
+
+.item "@$@{rfc2047:<<string>>@}"
+.index expansion||RFC 2047
+This operator encodes text according to the rules of RFC 2047. This is an
+encoding that is used in header lines to encode non-ASCII characters. It is
+assumed that the input string is in the encoding specified by the
+\headers@_charset\ option, which defaults to ISO-8859-1.
+If the string contains only characters in the range 33--126, and no instances
+of the characters
+.display asis
+? = ( ) < > @ , ; : \ " . [ ] _
+.endd
+it is not modified. Otherwise, the result is the RFC 2047 encoding, as a single
+`coded word'.
+
+
+.item "@$@{sha1:<<string>>@}"
+.index SHA-1 hash
+.index expansion||SHA-1 hashing
+The \sha1\ operator computes the SHA-1 hash value of the string, and returns it
+as a 40-digit hexadecimal number, in which any letters are in upper case.
+
+
+.item "@$@{stat:<<string>>@}"
+.index expansion||statting a file
+.index file||extracting characteristics
+The string, after expansion, must be a file path. A call to the \*stat()*\
+function is made for this path. If \*stat()*\ fails, an error occurs and the
+expansion fails. If it succeeds, the data from the stat replaces the item, as a
+series of <<name>>=<<value>> pairs, where the values are all numerical,
+except for the value of `smode'. The names are: `mode' (giving the mode as a
+4-digit octal number), `smode' (giving the mode in symbolic format as a
+10-character string, as for the \*ls*\ command), `inode', `device', `links',
+`uid', `gid', `size', `atime', `mtime', and `ctime'. You can extract individual
+fields using the \extract\ expansion item. \**Warning**\: The file size may be
+incorrect on 32-bit systems for files larger than 2GB.
+
+
+.item "@$@{strlen:<<string>>@}"
+.index expansion||string length
+.index string||length in expansion
+The item is replace by the length of the expanded string, expressed as a
+decimal number. \**Note**\: Do not confuse \strlen\ with \length\.
+
+
+.item "@$@{substr@_<<start>>@_<<length>>:<<string>>@}"
+.index \substr\
+.index substring extraction
+.index expansion||substring expansion
+The \substr\ operator is a simpler interface to the \substr\ function that can
+be used when the two parameters are fixed numbers (as opposed to strings that
+change when expanded). The effect is the same as
+.display
+@$@{substr@{<<start>>@}@{<<length>>@}@{<<string>>@}@}
+.endd
+See the description of the general \substr\ item above for details. The
+abbreviation \s\ can be used when \substr\ is used as an operator.
+
+.em
+.item "@$@{time@_interval:<<string>>@}"
+.index \time@_interval\
+.index time interval||formatting
+The argument (after sub-expansion) must be a sequence of decimal digits that
+represents an interval of time as a number of seconds. It is converted into a
+number of larger units and output in Exim's normal time format, for example,
+\"1w3d4h2m6s"\.
+.nem
+
+.item "@$@{uc:<<string>>@}"
+.index case forcing in strings
+.index string||case forcing
+.index upper casing
+.index expansion||case forcing
+This forces the letters in the string into upper-case.
+
+.enditems
+
+
+
+.section Expansion conditions
+.rset SECTexpcond "~~chapter.~~section"
+.index expansion||conditions
+The following conditions are available for testing by the \@$@{if\ construct
+while expanding strings:
+
+.startitems
+
+.item "!<<condition>>"
+.index expansion||negating a condition
+Preceding any condition with an exclamation mark negates the result of the
+condition.
+
+.item "<<symbolic operator>> @{<<string1>>@}@{<<string2>>@}"
+.index numeric comparison
+.index expansion||numeric comparison
+There are a number of symbolic operators for doing numeric comparisons. They
+are:
+.display
+.tabs 8
+= $t $rm{equal}
+== $t $rm{equal}
+> $t $rm{greater}
+>= $t $rm{greater or equal}
+< $t $rm{less}
+<= $t $rm{less or equal}
+.endd
+For example,
+.display asis
+${if >{$message_size}{10M} ...
+.endd
+Note that the general negation operator provides for inequality testing. The
+two strings must take the form of optionally signed decimal integers,
+optionally followed by one of the letters `K' or `M' (in either upper or lower
+case), signifying multiplication by 1024 or 1024$*$1024, respectively.
+
+.item "crypteq @{<<string1>>@}@{<<string2>>@}"
+.index expansion||encrypted comparison
+.index encrypted strings, comparing
+This condition is included in the Exim binary if it is built to support any
+authentication mechanisms (see chapter ~~CHAPSMTPAUTH). Otherwise, it is
+necessary to define \\SUPPORT@_CRYPTEQ\\ in \(Local/Makefile)\ to get \crypteq\
+included in the binary.
+
+The \crypteq\ condition has two arguments. The first is encrypted and compared
+against the second, which is already encrypted. The second string may be in the
+LDAP form for storing encrypted strings, which starts with the encryption type
+in curly brackets, followed by the data. If the second string does not begin
+with `{' it is assumed to be encrypted with \*crypt()*\
+or \*crypt16()*\ (see below),
+since such strings cannot begin with `{'. Typically this will be a field from a
+password file.
+
+An example of an encrypted string in LDAP form is:
+.display asis
+{md5}CY9rzUYh03PK3k6DJie09g==
+.endd
+If such a string appears directly in an expansion, the curly brackets have to
+be quoted, because they are part of the expansion syntax. For example:
+.display asis
+${if crypteq {test}{\{md5\}CY9rzUYh03PK3k6DJie09g==}{yes}{no}}
+.endd
+The following encryption types
+(whose names are matched case-independently)
+are supported:
+.numberpars $.
+.index MD5 hash
+.index base64 encoding||in encrypted password
+\@{md5@}\ computes the MD5 digest of the first string, and expresses this as
+printable characters to compare with the remainder of the second string. If the
+length of the comparison string is 24, Exim assumes that it is base64 encoded
+(as in the above example). If the length is 32, Exim assumes that it is a
+hexadecimal encoding of the MD5 digest. If the length not 24 or 32, the
+comparison fails.
+.nextp
+.index SHA-1 hash
+\@{sha1@}\ computes the SHA-1 digest of the first string, and expresses this as
+printable characters to compare with the remainder of the second string. If the
+length of the comparison string is 28, Exim assumes that it is base64 encoded.
+If the length is 40, Exim assumes that it is a hexadecimal encoding of the
+SHA-1 digest. If the length is not 28 or 40, the comparison fails.
+.nextp
+.index \*crypt()*\
+\@{crypt@}\ calls the \*crypt()*\ function, which uses only the first eight
+characters of the password.
+.nextp
+.index \*crypt16()*\
+\@{crypt16@}\ calls the \*crypt16()*\ function (also known as \*bigcrypt()*\),
+which uses up to 16 characters of the password.
+.endp
+Exim has its own version of \*crypt16()*\ (which is just a double call to
+\*crypt()*\). For operating systems that have their own version, setting
+\\HAVE@_CRYPT16\\ in \(Local/Makefile)\ when building Exim causes it to use the
+operating system version instead of its own. This option is set by default in
+the OS-dependent \(Makefile)\ for those operating systems that are known to
+support \*crypt16()*\.
+
+If you do not put any curly bracket encryption type in a \crypteq\ comparison,
+the default is either \"@{crypt@}"\ or \"@{crypt16@}"\, as determined by the
+setting of \\DEFAULT@_CRYPT\\ in \(Local/Makefile)\. The default default is
+\"@{crypt@}"\. Whatever the default, you can always use either function by
+specifying it explicitly in curly brackets.
+
+Note that if a password is no longer than 8 characters, the results of
+encrypting it with \*crypt()*\ and \*crypt16()*\ are identical. That means that
+\*crypt16()*\ is backwards compatible, as long as nobody feeds it a password
+longer than 8 characters.
+
+
+.item "def:<<variable name>>"
+.index expansion||checking for empty variable
+The \def\ condition must be followed by the name of one of the expansion
+variables defined in section ~~SECTexpvar. The condition is true if the named
+expansion variable does not contain the empty string, for example
+.display asis
+${if def:sender_ident {from $sender_ident}}
+.endd
+Note that the variable name is given without a leading \@$\ character. If the
+variable does not exist, the expansion fails.
+
+.item "def:header@_<<header name>>:##or##def:h@_<<header name>>:"
+.index expansion||checking header line existence
+This condition is true if a message is being processed and the named header
+exists in the message. For example,
+.display asis
+${if def:header_reply-to:{$h_reply-to:}{$h_from:}}
+.endd
+Note that no \@$\ appears before \header@_\ or \h@_\ in the condition,
+and that header names must be terminated by colons if white space does not
+follow.
+
+.item "eq @{<<string1>>@}@{<<string2>>@}"
+.item "eqi @{<<string1>>@}@{<<string2>>@}"
+.index string||comparison
+.index expansion||string comparison
+The two substrings are first expanded. The condition is true if the two
+resulting strings are identical: for \eq\ the comparison includes the case of
+letters, whereas for \eqi\ the comparison is case-independent.
+
+.item "exists @{<<file name>>@}"
+.index expansion||file existence test
+.index file||existence test
+The substring is first expanded and then interpreted as an absolute path. The
+condition is true if the named file (or directory) exists. The existence test
+is done by calling the \*stat()*\ function. The use of the \exists\ test in
+users' filter files may be locked out by the system administrator.
+
+.item "first@_delivery"
+.index delivery||first
+.index first delivery
+.index expansion||first delivery test
+This condition, which has no data, is true during a message's first delivery
+attempt. It is false during any subsequent delivery attempts.
+
+.em
+.item "ge @{<<string1>>@}@{<<string2>>@}"
+.item "gei @{<<string1>>@}@{<<string2>>@}"
+.index string||comparison
+.index expansion||string comparison
+The two substrings are first expanded. The condition is true if the first
+string is lexically greater than or equal to the second string: for \ge\ the
+comparison includes the case of letters, whereas for \gei\ the comparison is
+case-independent.
+
+.item "gt @{<<string1>>@}@{<<string2>>@}"
+.item "gti @{<<string1>>@}@{<<string2>>@}"
+.index string||comparison
+.index expansion||string comparison
+The two substrings are first expanded. The condition is true if the first
+string is lexically greater than the second string: for \gt\ the comparison
+includes the case of letters, whereas for \gti\ the comparison is
+case-independent.
+.nem
+
+.item "isip @{<<string>>@}" 8
+.item "isip4 @{<<string>>@}"
+.item "isip6 @{<<string>>@}"
+.index IP address||testing string format
+.index string||testing for IP address
+The substring is first expanded, and then tested to see if it has the form of
+an IP address. Both IPv4 and IPv6 addresses are valid for \isip\, whereas
+\isip4\ and \isip6\ test just for IPv4 or IPv6 addresses, respectively. For
+example, you could use
+.display asis
+${if isip4{$sender_host_address}...
+.endd
+to test which version of IP an incoming SMTP connection is using.
+
+
+.item "ldapauth @{<<ldap query>>@}"
+.index LDAP||use for authentication
+.index expansion||LDAP authentication test
+This condition supports user authentication using LDAP. See section ~~SECTldap
+for details of how to use LDAP in lookups and the syntax of queries. For this
+use, the query must contain a user name and password. The query itself is not
+used, and can be empty. The condition is true if
+the password is not empty, and the user name and password are accepted by the
+LDAP server. An empty password is rejected without calling LDAP because LDAP
+binds with an empty password are considered anonymous regardless of
+the username, and will succeed in most configurations.
+See chapter ~~CHAPSMTPAUTH for details of SMTP authentication, and chapter
+~~CHAPplaintext for an example of how this can be used.
+
+
+.em
+.item "le @{<<string1>>@}@{<<string2>>@}"
+.item "lei @{<<string1>>@}@{<<string2>>@}"
+.index string||comparison
+.index expansion||string comparison
+The two substrings are first expanded. The condition is true if the first
+string is lexically less than or equal to the second string: for \le\ the
+comparison includes the case of letters, whereas for \lei\ the comparison is
+case-independent.
+
+.item "lt @{<<string1>>@}@{<<string2>>@}"
+.item "lti @{<<string1>>@}@{<<string2>>@}"
+.index string||comparison
+.index expansion||string comparison
+The two substrings are first expanded. The condition is true if the first
+string is lexically less than the second string: for \lt\ the comparison
+includes the case of letters, whereas for \lti\ the comparison is
+case-independent.
+.nem
+
+
+.item "match @{<<string1>>@}@{<<string2>>@}"
+.index expansion||regular expression comparison
+.index regular expressions||match in expanded string
+The two substrings are first expanded. The second is then treated as a regular
+expression and applied to the first. Because of the pre-expansion, if the
+regular expression contains dollar, or backslash characters, they must be
+escaped. Care must also be taken if the regular expression contains braces
+(curly brackets). A closing brace must be escaped so that it is not taken as a
+premature termination of <<string2>>. The easiest approach is to use the
+\"@\N"\ feature to disable expansion of the regular expression.
+For example,
+.display asis
+${if match {$local_part}{\N^\d{3}\N} ...
+.endd
+If the whole expansion string is in double quotes, further escaping of
+backslashes is also required.
+
+The condition is true if the regular expression match succeeds.
+.em
+The regular expression is not required to begin with a circumflex
+metacharacter, but if there is no circumflex, the expression is not anchored,
+and it may match anywhere in the subject, not just at the start. If you want
+the pattern to match at the end of the subject, you must include the \"@$"\
+metacharacter at an appropriate point.
+.nem
+
+.index numerical variables (\$1$\, \$2$\, etc)||in \if\ expansion
+At the start of an \if\ expansion the values of the numeric variable
+substitutions \$1$\ etc. are remembered. Obeying a \match\ condition that
+succeeds causes them to be reset to the substrings of that condition and they
+will have these values during the expansion of the success string. At the end
+of the \if\ expansion, the previous values are restored. After testing a
+combination of conditions using \or\, the subsequent values of the numeric
+variables are those of the condition that succeeded.
+
+.em
+.item "match@_domain @{<<string1>>@}@{<<string2>>@}"
+.item "match@_address @{<<string1>>@}@{<<string2>>@}"
+.item "match@_local@_part @{<<string1>>@}@{<<string2>>@}"
+.index domain list||in expansion condition
+.index address list||in expansion condition
+.index local part list||in expansion condition
+These conditions make it possible to test domain, address, and local
+part lists within expansions. Each condition requires two arguments: an item
+and a list to match. A trivial example is:
+.display asis
+${if match_domain{a.b.c}{x.y.z:a.b.c:p.q.r}{yes}{no}}
+.endd
+In each case, the second argument may contain any of the allowable items for a
+list of the appropriate type. Also, because the second argument (after
+expansion) is a standard form of list, it is possible to refer to a named list.
+Thus, you can use conditions like this:
+.display asis
+${if match_domain{$domain}{+local_domains}{...
+.endd
+.index \"+caseful"\
+For address lists, the matching starts off caselessly, but the \"+caseful"\
+item can be used, as in all address lists, to cause subsequent items to
+have their local parts matched casefully. Domains are always matched
+caselessly.
+
+\**Note**\: Host lists are \*not*\ supported in this way. This is because
+hosts have two identities: a name and an IP address, and it is not clear
+how to specify cleanly how such a test would work. At least, I haven't come
+up with anything yet.
+.nem
+
+.item "pam {<<string1>>:<<string2>>:...@}"
+.index PAM authentication
+.index \\AUTH\\||with PAM
+.index Solaris||PAM support
+.index expansion||PAM authentication test
+\*Pluggable Authentication Modules*\
+(\?http://www.kernel.org/pub/linux/libs/pam/?\)
+are a facility which is available in the latest releases of Solaris and in some
+GNU/Linux distributions. The Exim support, which is intended for use in
+conjunction with the SMTP \\AUTH\\ command, is available only if Exim is
+compiled with
+.display asis
+SUPPORT_PAM=yes
+.endd
+in \(Local/Makefile)\. You probably need to add \-lpam-\ to \\EXTRALIBS\\, and
+in some releases of GNU/Linux \-ldl-\ is also needed.
+
+The argument string is first expanded, and the result must be a colon-separated
+list of strings.
+Leading and trailing whitespace is ignored.
+The PAM module is initialized with the service name `exim' and the user name
+taken from the first item in the colon-separated data string (<<string1>>). The
+remaining items in the data string are passed over in response to requests from
+the authentication function. In the simple case there will only be one request,
+for a password, so the data consists of just two strings.
+
+There can be problems if any of the strings are permitted to contain colon
+characters. In the usual way, these have to be doubled to avoid being taken as
+separators. If the data is being inserted from a variable, the \sg\ expansion
+item can be used to double any existing colons. For example, the configuration
+of a LOGIN authenticator might contain this setting:
+.display asis
+server_condition = ${if pam{$1:${sg{$2}{:}{::}}}{yes}{no}}
+.endd
+For a PLAIN authenticator you could use:
+.display asis
+server_condition = ${if pam{$2:${sg{$3}{:}{::}}}{yes}{no}}
+.endd
+In some operating systems, PAM authentication can be done only from a process
+running as root. Since Exim is running as the Exim user when receiving
+messages, this means that PAM cannot be used directly in those systems.
+A patched version of the \*pam@_unix*\ module that comes with the
+Linux PAM package is available from \?http:@/@/www.e-admin.de/pam@_exim/?\.
+The patched module allows one special uid/gid combination, in addition to root,
+to authenticate. If you build the patched module to allow the Exim user and
+group, PAM can then be used from an Exim authenticator.
+
+
+.item "pwcheck {<<string1>>:<<string2>>@}"
+.index \*pwcheck*\ daemon
+.index Cyrus
+.index expansion||\*pwcheck*\ authentication test
+This condition supports user authentication using the Cyrus \*pwcheck*\ daemon.
+This is one way of making it possible for passwords to be checked by a process
+that is not running as root.
+\**Note:**\ The use of \*pwcheck*\ is now deprecated. Its replacement is
+\*saslauthd*\ (see below).
+
+The pwcheck support is not included in Exim by default. You need to specify
+the location of the pwcheck daemon's socket in \(Local/Makefile)\ before
+building Exim. For example:
+.display asis
+CYRUS_PWCHECK_SOCKET=/var/pwcheck/pwcheck
+.endd
+You do not need to install the full Cyrus software suite in order to use
+the pwcheck daemon. You can compile and install just the daemon alone
+from the Cyrus SASL library. Ensure that \*exim*\ is the only user that has
+access to the \(/var/pwcheck)\ directory.
+
+The \pwcheck\ condition takes one argument, which must be the user name and
+password, separated by a colon. For example, in a LOGIN authenticator
+configuration, you might have this:
+.display asis
+server_condition = ${if pwcheck{$1:$2}{1}{0}}
+.endd
+
+.item "queue@_running"
+.index queue runner||detecting when delivering from
+.index expansion||queue runner test
+This condition, which has no data, is true during delivery attempts that are
+initiated by queue runner processes, and false otherwise.
+
+
+.item "radius {<<authentication string>>@}"
+.index Radius
+.index expansion||Radius authentication
+Radius authentication (RFC 2865) is supported in a similar way to PAM. You must
+set \\RADIUS@_CONFIG@_FILE\\ in \(Local/Makefile)\ to specify the location of
+the Radius client configuration file in order to build Exim with Radius
+support.
+You may also have to supply a suitable setting in \\EXTRALIBS\\ so that the
+Radius library can be found when Exim is linked.
+The string specified by \\RADIUS@_CONFIG@_FILE\\ is expanded and passed to the
+Radius client library, which calls the Radius server. The condition is true if
+the authentication is successful. For example
+.display
+server@_condition = @$@{if radius@{<<arguments>>@}@{yes@}@{no@}@}
+.endd
+
+
+
+.item "saslauthd @{@{<<user>>@}@{<<password>>@}@{<<service>>@}@{<<realm>>@}@}"
+.index \*saslauthd*\ daemon
+.index Cyrus
+.index expansion||\*saslauthd*\ authentication test
+This condition supports user authentication using the Cyrus \*saslauthd*\
+daemon. This replaces the older \*pwcheck*\ daemon, which is now deprecated.
+Using this daemon is one way of making it possible for passwords to be checked
+by a process that is not running as root.
+
+The saslauthd support is not included in Exim by default. You need to specify
+the location of the saslauthd daemon's socket in \(Local/Makefile)\ before
+building Exim. For example:
+.display asis
+CYRUS_SASLAUTHD_SOCKET=/var/state/saslauthd/mux
+.endd
+You do not need to install the full Cyrus software suite in order to use
+the saslauthd daemon. You can compile and install just the daemon alone
+from the Cyrus SASL library.
+
+Up to four arguments can be supplied to the \saslauthd\ condition, but only two
+are mandatory. For example:
+.display asis
+server_condition = ${if saslauthd{{$1}{$2}}{1}{0}}
+.endd
+The service and the realm are optional (which is why the arguments are enclosed
+in their own set of braces). For details of the meaning of the service and
+realm, and how to run the daemon, consult the Cyrus documentation.
+
+.enditems
+
+
+
+.section Combining expansion conditions
+.index expansion||combining conditions
+Several conditions can be tested at once by combining them using the \and\ and
+\or\ combination conditions. Note that \and\ and \or\ are complete conditions
+on their own, and precede their lists of sub-conditions. Each sub-condition
+must be enclosed in braces within the overall braces that contain the list. No
+repetition of \if\ is used.
+
+.startitems
+
+.item "or @{@{<<cond1>>@}@{<<cond2>>@}...@}"
+.index `or' expansion condition
+.index expansion||`or' of conditions
+The sub-conditions are evaluated from left to right. The condition is true if
+any one of the sub-conditions is true.
+For example,
+.display asis
+${if or {{eq{$local_part}{spqr}}{eq{$domain}{testing.com}}}...
+.endd
+When a true sub-condition is found, the following ones are parsed but not
+evaluated. If there are several `match' sub-conditions the values of the
+numeric variables afterwards are taken from the first one that succeeds.
+
+.item "and @{@{<<cond1>>@}@{<<cond2>>@}...@}"
+.index `and' expansion condition
+.index expansion||`and' of conditions
+The sub-conditions are evaluated from left to right. The condition is true if
+all of the sub-conditions are true. If there are several `match'
+sub-conditions, the values of the numeric variables afterwards are taken from
+the last one. When a false sub-condition is found, the following ones are
+parsed but not evaluated.
+
+.enditems
+
+
+
+.section Expansion variables
+.rset SECTexpvar "~~chapter.~~section"
+.index expansion||variables, list of
+
+The variables that are available for use in expansion strings are:
+
+.push
+.indent 2em
+.tempindent 0
+.index numerical variables (\$1$\, \$2$\, etc)
+\$0$\, \$1$\, etc: When a \match\ expansion condition succeeds, these
+variables contain the captured substrings identified by the regular expression
+during subsequent processing of the success string of the containing \if\
+expansion item. They may also be set externally by some other matching process
+which precedes the expansion of the string. For example, the commands available
+in Exim filter files include an \if\ command with its own regular expression
+matching condition.
+
+.tempindent 0
+\$acl@_c0$\ -- \$acl@_c9$\: Values can be placed in these variables by the
+\set\ modifier in an ACL. The values persist throughout the lifetime of an SMTP
+connection. They can be used to pass information between ACLs and different
+invocations of the same ACL.
+When a message is received, the values of these variables are saved with the
+message, and can be accessed by filters, routers, and transports during
+subsequent delivery.
+
+.tempindent 0
+\$acl@_m0$\ -- \$acl@_m9$\: Values can be placed in these variables by the
+\set\ modifier in an ACL. They retain their values while a message is being
+received, but are reset afterwards. They are also reset by \\MAIL\\, \\RSET\\,
+\\EHLO\\, \\HELO\\, and after starting a TLS session.
+When a message is received, the values of these variables are saved with the
+message, and can be accessed by filters, routers, and transports during
+subsequent delivery.
+
+
+.tempindent 0
+\$acl@_verify@_message$\: During the expansion of the \message\ and
+\log@_message\ modifiers in an ACL statement after an address verification has
+failed, this variable contains the original failure message that will be
+overridden by the expanded string.
+
+.tempindent 0
+\$address@_data$\: This variable is set by means of the \address@_data\
+option in routers. The value then remains with the address while it is
+processed by subsequent routers and eventually a transport. If the transport is
+handling multiple addresses, the value from the first address is used. See
+chapter ~~CHAProutergeneric for more details.
+\**Note**\: the contents of \$address@_data$\ are visible in user filter files.
+
+If \$address@_data$\ is set when the routers are called to verify an address
+from an ACL, the final value remains available in subsequent conditions in the
+ACL statement. If routing the address caused it to be redirected to a single
+address, the child address is also routed as part of the verification, and in
+this case the final value of \$address@_data$\ is from the child's routing.
+
+.tempindent 0
+\$address@_file$\: When, as a result of aliasing, forwarding, or filtering, a
+message is directed to a specific file, this variable holds the name of the
+file when the transport is running. At other times, the variable is empty. For
+example, using the default configuration, if user \r2d2\ has a \(.forward)\
+file containing
+.display asis
+/home/r2d2/savemail
+.endd
+then when the \%address@_file%\ transport is running, \$address@_file$\
+contains `/home/r2d2/savemail'.
+.index Sieve filter||value of \$address@_file$\
+For Sieve filters, the value may be `inbox' or a relative folder name. It is
+then up to the transport configuration to generate an appropriate absolute path
+to the relevant file.
+
+
+.tempindent 0
+\$address@_pipe$\: When, as a result of aliasing or forwarding, a message is
+directed to a pipe, this variable holds the pipe command when the transport is
+running.
+
+.index authentication||id
+.tempindent 0
+\$authenticated@_id$\: When a server successfully authenticates a client it may
+be configured to preserve some of the authentication information in the
+variable \$authenticated@_id$\ (see chapter ~~CHAPSMTPAUTH). For example, a
+user/password authenticator configuration might preserve the user name for use
+in the routers. When a message is submitted locally (that is, not over a TCP
+connection), the value of \$authenticated@_id$\ is the login name of the
+calling process.
+
+.index sender||authenticated
+.index authentication||sender
+.index \\AUTH\\||on \\MAIL\\ command
+.tempindent 0
+\$authenticated@_sender$\:
+.em
+When acting as a server, Exim takes note of the \\AUTH=\\ parameter on an
+incoming SMTP \\MAIL\\ command
+.nem
+if it believes the sender is sufficiently trusted, as described in section
+~~SECTauthparamail. Unless the data is the string `@<@>', it is set as the
+authenticated sender of the message, and the value is available during delivery
+in the \$authenticated@_sender$\ variable. If the sender is not trusted, Exim
+accepts the syntax of \\AUTH=\\, but ignores the data.
+
+When a message is submitted locally (that is, not over a TCP connection), the
+value of \$authenticated@_sender$\ is an address constructed from the login
+name of the calling process and \$qualify@_domain$\.
+
+
+.index authentication||failure
+.tempindent 0
+\$authentication@_failed$\:
+This variable is set to `1' in an Exim server if a client issues an \\AUTH\\
+command that does not succeed. Otherwise it is set to `0'. This makes it
+possible to distinguish between `did not try to authenticate'
+(\$sender@_host@_authenticated$\ is empty and \$authentication__failed$\ is set
+to `0') and `tried to authenticate but failed' (\$sender@_host@_authenticated$\
+is empty and \$authentication@_failed$\ is set to `1'). Failure includes any
+negative response to an \\AUTH\\ command, including (for example) an attempt to
+use an undefined mechanism.
+
+
+.index message||body, line count
+.index body of message||line count
+.tempindent 0
+\$body@_linecount$\:
+When a message is being received or delivered, this variable contains the
+number of lines in the message's body.
+
+.index message||body, binary zero count
+.index body of message||binary zero count
+.index binary zero||in message body
+.tempindent 0
+.em
+\$body@_zerocount$\:
+When a message is being received or delivered, this variable contains the
+number of binary zero bytes in the message's body.
+.nem
+
+.tempindent 0
+\$bounce@_recipient$\:
+This is set to the recipient address of a bounce message while Exim is creating
+it. It is useful if a customized bounce message text file is in use (see
+chapter ~~CHAPemsgcust).
+
+.tempindent 0
+\$bounce@_return@_size@_limit$\: This contains the value set in the
+\bounce@_return@_size@_limit\ option, rounded up to a multiple of 1000. It is
+useful when a customized error message text file is in use (see chapter
+~~CHAPemsgcust).
+
+.index gid (group id)||caller
+.tempindent 0
+\$caller@_gid$\: The
+.em
+real
+.nem
+group id under which the process that called Exim was
+running. This is not the same as the group id of the originator of a message
+(see \$originator@_gid$\). If Exim re-execs itself, this variable in the new
+incarnation normally contains the Exim gid.
+
+.index uid (user id)||caller
+.tempindent 0
+\$caller@_uid$\: The
+.em
+real
+.nem
+user id under which the process that called Exim was
+running. This is not the same as the user id of the originator of a message
+(see \$originator@_uid$\). If Exim re-execs itself, this variable in the new
+incarnation normally contains the Exim uid.
+
+.tempindent 0
+\$compile@_date$\: The date on which the Exim binary was compiled.
+
+.tempindent 0
+\$compile@_number$\: The building process for Exim keeps a count of the number
+of times it has been compiled. This serves to distinguish different
+compilations of the same version of the program.
+
+.index black list (DNS)
+.tempindent 0
+\$dnslist@_domain$\: When a client host is found to be on a DNS (black) list,
+the list's domain name is put into this variable so that it can be included in
+the rejection message.
+
+.tempindent 0
+\$dnslist@_text$\: When a client host is found to be on a DNS (black) list, the
+contents of any associated TXT record are placed in this variable.
+
+.tempindent 0
+\$dnslist@_value$\: When a client host is found to be on a DNS (black) list,
+the IP address from the resource record is placed in this variable.
+If there are multiple records, all the addresses are included, comma-space
+separated.
+
+.tempindent 0
+\$domain$\: When an address is being routed, or delivered on its own, this
+variable contains the domain. Global address rewriting happens when a message
+is received, so the value of \$domain$\ during routing and delivery is the
+value after rewriting. \$domain$\ is set during user filtering, but not during
+system filtering, because a message may have many recipients and the system
+filter is called just once.
+
+When more than one address is being delivered at once (for example, several
+\\RCPT\\ commands in one SMTP delivery), \$domain$\ is set only if they all
+have the same domain. Transports can be restricted to handling only one domain
+at a time if the value of \$domain$\ is required at transport time -- this is
+the default for local transports. For further details of the environment in
+which local transports are run, see chapter ~~CHAPenvironment.
+
+.index \delay@_warning@_condition\
+At the end of a delivery, if all deferred addresses have the same domain, it is
+set in \$domain$\ during the expansion of \delay@_warning@_condition\.
+
+The \$domain$\ variable is also used in some other circumstances:
+.numberpars $.
+When an ACL is running for a \\RCPT\\ command, \$domain$\ contains the domain
+of the recipient address.
+\**Note:**\ the domain of the sender address is in \$sender@_address@_domain$\
+at \\MAIL\\ time and at \\RCPT\\ time. \$domain$\ is not set for the \\MAIL\\
+ACL.
+.nextp
+When a rewrite item is being processed (see chapter ~~CHAPrewrite), \$domain$\
+contains the domain portion of the address that is being rewritten; it can be
+used in the expansion of the replacement address, for example, to rewrite
+domains by file lookup.
+.nextp
+With one important exception, whenever a domain list is being scanned,
+\$domain$\ contains the subject domain. \**Exception**\: When a domain list in
+a \sender@_domains\ condition in an ACL is being processed, the subject domain
+is in \$sender@_address@_domain$\ and not in \$domain$\. It works this way so
+that, in a \\RCPT\\ ACL, the sender domain list can be dependent on the
+recipient domain (which is what is in \$domain$\ at this time).
+.nextp
+.index \\ETRN\\||value of \$domain$\
+.index \smtp@_etrn@_command\
+When the \smtp@_etrn@_command\ option is being expanded, \$domain$\ contains
+the complete argument of the \\ETRN\\ command (see section ~~SECTETRN).
+.endp
+
+.tempindent 0
+\$domain@_data$\: When the \domains\ option on a router matches a domain by
+means of a lookup, the data read by the lookup is available during the running
+of the router as \$domain@_data$\. In addition, if the driver routes the
+address to a transport, the value is available in that transport. If the
+transport is handling multiple addresses, the value from the first address is
+used.
+
+\$domain@_data$\ is also set when the \domains\ condition in an ACL matches a
+domain by means of a lookup. The data read by the lookup is available during
+the rest of the ACL statement. In all other situations, this variable expands
+to nothing.
+
+.em
+.tempindent 0
+\$exim@_gid$\: This variable contains the numerical value of the Exim group id.
+
+.tempindent 0
+\$exim@_path$\: This variable contains the path to the Exim binary.
+
+.tempindent 0
+\$exim@_uid$\: This variable contains the numerical value of the Exim user id.
+.nem
+
+.tempindent 0
+\$header@_<<name>>$\: This is not strictly an expansion variable. It is
+expansion syntax for inserting the message header line with the given name.
+Note that the name must be terminated by colon or white space, because it may
+contain a wide variety of characters.
+Note also that braces must \*not*\ be used.
+
+.tempindent 0
+\$home$\:
+When the \check@_local@_user\ option is set for a router, the user's home
+directory is placed in \$home$\ when the check succeeds. In particular, this
+means it is set during the running of users' filter files. A router may also
+explicitly set a home directory for use by a transport; this can be overridden
+by a setting on the transport itself.
+
+When running a filter test via the \-bf-\ option, \$home$\ is set to the value
+of the environment variable \\HOME\\.
+
+.tempindent 0
+\$host$\:
+When the \%smtp%\ transport is expanding its options for encryption using TLS,
+\$host$\ contains the name of the host to which it is connected. Likewise, when
+used in the client part of an authenticator configuration (see chapter
+~~CHAPSMTPAUTH), \$host$\ contains the name of the server to which the client
+is connected.
+.index transport||filter
+.index filter||transport filter
+When used in a transport filter (see chapter ~~CHAPtransportgeneric) \$host$\
+refers to the host involved in the current connection. When a local transport
+is run as a result of a router that sets up a host list, \$host$\ contains the
+name of the first host.
+
+.tempindent 0
+\$host@_address$\:
+This variable is set to the remote host's IP address whenever \$host$\ is set
+for a remote connection.
+
+.tempindent 0
+\$host@_data$\:
+If a \hosts\ condition in an ACL is satisfied by means of a lookup, the result
+of the lookup is made available in the \$host@_data$\ variable. This
+allows you, for example, to do things like this:
+.display asis
+deny hosts = net-lsearch;/some/file
+ message = $host_data
+.endd
+
+.index host||name lookup, failure of
+.tempindent 0
+\$host@_lookup@_failed$\:
+This variable contains `1' if the message came from a remote host and there was
+an attempt to look up the host's name from its IP address, but the attempt
+failed. Otherwise the value of the variable is `0'.
+.em
+Exim checks that a forward lookup of at least one of the names it receives from
+a reverse lookup yields the original IP address. If this is not the case, Exim
+does not accept the looked up name(s), and \$host@_lookup@_failed$\ is set to
+`1'. Thus, being able to find a name from an IP address (for example, the
+existence of a PTR record in the DNS) is not sufficient on its own for the
+success of a host name lookup.
+.nem
+
+.tempindent 0
+\$inode$\:
+The only time this variable is set is while expanding the \directory@_file\
+option in the \%appendfile%\ transport. The variable contains the inode number
+of the temporary file which is about to be renamed. It can be used to construct
+a unique name for the file.
+
+.tempindent 0
+\$interface@_address$\:
+When a message is received over a TCP/IP connection, this variable contains the
+address of the local IP interface. See also the \-oMi-\ command line option.
+This variable can be used in ACLs and also, for example, to make the file name
+for a TLS certificate depend on which interface is being used.
+
+.tempindent 0
+\$interface@_port$\:
+When a message is received over a TCP/IP connection, this variable contains the
+local port number. See also the \-oMi-\ command line option.
+This variable can be used in ACLs and also, for example, to make the file name
+for a TLS certificate depend on which port is being used.
+
+.tempindent 0
+\$ldap@_dn$\:
+This variable, which is available only when Exim is compiled with LDAP support,
+contains the DN from the last entry in the most recently successful LDAP
+lookup.
+
+
+.tempindent 0
+\$load@_average$\:
+This variable contains the system load average, multiplied by 1000 to that it
+is an integer. For example, if the load average is 0.21, the value of the
+variable is 210. The value is recomputed every time the variable is referenced.
+
+.tempindent 0
+\$local@_part$\: When an address is being routed, or delivered on its own, this
+variable contains the local part. When a number of addresses are being
+delivered together (for example, multiple \\RCPT\\ commands in an SMTP
+session), \$local@_part$\ is not set.
+
+Global address rewriting happens when a message is received, so the value of
+\$local@_part$\ during routing and delivery is the value after rewriting.
+\$local@_part$\ is set during user filtering, but not during system filtering,
+because a message may have many recipients and the system filter is called just
+once.
+
+If a local part prefix or suffix has been recognized, it is not included in the
+value of \$local@_part$\ during routing and subsequent delivery. The values of
+any prefix or suffix are in \$local@_part@_prefix$\ and
+\$local@_part@_suffix$\, respectively.
+
+When a message is being delivered to a file, pipe, or autoreply transport as a
+result of aliasing or forwarding, \$local@_part$\ is set to the local part of
+the parent address, not to the file name or command (see \$address@_file$\ and
+\$address@_pipe$\).
+
+When an ACL is running for a \\RCPT\\ command, \$local@_part$\ contains the
+local part of the recipient address.
+
+When a rewrite item is being processed (see chapter ~~CHAPrewrite),
+\$local@_part$\ contains the local part of the address that is being rewritten;
+it can be used in the expansion of the replacement address, for example.
+
+In all cases, all quoting is removed from the local part. For example, for both
+the addresses
+.display asis
+"abc:xyz"@test.example
+abc\:xyz@test.example
+.endd
+the value of \$local@_part$\ is
+.display asis
+abc:xyz
+.endd
+If you use \$local@_part$\ to create another address, you should always wrap it
+inside a quoting operator. For example, in a \%redirect%\ router you could have:
+.display asis
+data = ${quote_local_part:$local_part}@new.domain.example
+.endd
+.em
+\**Note**\: The value of \$local@_part$\ is normally lower cased. If you want
+to process local parts in a case-dependent manner in a router, you can set the
+\caseful@_local@_part\ option (see chapter ~~CHAProutergeneric).
+.nem
+
+.tempindent 0
+\$local@_part@_data$\:
+When the \local@_parts\ option on a router matches a local part by means of a
+lookup, the data read by the lookup is available during the running of the
+router as \$local@_part@_data$\. In addition, if the driver routes the address
+to a transport, the value is available in that transport. If the transport is
+handling multiple addresses, the value from the first address is used.
+
+\$local@_part@_data$\ is also set when the \local@_parts\ condition in an ACL
+matches a local part by means of a lookup. The data read by the lookup is
+available during the rest of the ACL statement. In all other situations, this
+variable expands to nothing.
+
+.tempindent 0
+\$local@_part@_prefix$\: When an address is being routed or delivered, and a
+specific prefix for the local part was recognized, it is available in this
+variable, having been removed from \$local@_part$\.
+
+.tempindent 0
+\$local@_part@_suffix$\: When an address is being routed or delivered, and a
+specific suffix for the local part was recognized, it is available in this
+variable, having been removed from \$local@_part$\.
+
+.tempindent 0
+\$local@_scan@_data$\: This variable contains the text returned by the
+\*local@_scan()*\ function when a message is received. See chapter
+~~CHAPlocalscan for more details.
+
+.tempindent 0
+\$local@_user@_gid$\: See \$local@_user@_uid$\.
+
+.tempindent 0
+\$local@_user@_uid$\: This variable and \$local@_user@_gid$\ are set to
+the uid and gid after the \check__local__user\ router precondition succeeds.
+This means that their values are available for the remaining preconditions
+(\senders\, \require@_files\, and \condition\), for the \address@_data\
+expansion, and for any router-specific expansions. At all other times, the
+values in these variables are \"(uid@_t)(-1)"\ and \"(gid@_t)(-1)"\,
+respectively.
+
+
+.tempindent 0
+\$localhost@_number$\: This contains the expanded value of the
+\localhost@_number\ option. The expansion happens after the main options have
+been read.
+
+.tempindent 0
+\$mailstore@_basename$\: This variable is set only when doing deliveries in
+`mailstore' format in the \%appendfile%\ transport. During the expansion of the
+\mailstore@_prefix\, \mailstore@_suffix\, \message__prefix\, and
+\message@_suffix\ options, it contains the basename of the files that are being
+written, that is, the name without the `.tmp', `.env', or `.msg' suffix. At all
+other times, this variable is empty.
+
+.index message||age of
+.tempindent 0
+\$message@_age$\: This variable is set at the start of a delivery attempt to
+contain the number of seconds since the message was received. It does not
+change during a single delivery attempt.
+
+.index body of message||expansion variable
+.index message||body, in expansion
+.index binary zero||in message body
+.tempindent 0
+\$message@_body$\: This variable contains the initial portion of a message's
+body while it is being delivered, and is intended mainly for use in filter
+files. The maximum number of characters of the body that are put into the
+variable is set by the \message@_body@_visible\ configuration option; the
+default is 500. Newlines are converted into spaces to make it easier to search
+for phrases that might be split over a line break.
+Binary zeros are also converted into spaces.
+
+.index body of message||expansion variable
+.index message||body, in expansion
+.tempindent 0
+\$message@_body@_end$\: This variable contains the final portion of a message's
+body while it is being delivered. The format and maximum size are as for
+\$message@_body$\.
+
+.index body of message||size
+.index message||body, size
+.tempindent 0
+\$message@_body@_size$\: When a message is being processed, this variable
+contains the size of the body in bytes. The count starts from the character
+after the blank line that separates the body from the header. Newlines are
+included in the count. See also \$message@_size$\ and \$body@_linecount$\.
+
+.tempindent 0
+\$message@_headers$\:
+This variable contains a concatenation of all the header lines when a message
+is being processed, except for lines added by routers or transports. The header
+lines are separated by newline characters.
+
+.tempindent 0
+\$message@_id$\:
+When a message is being received or delivered, this variable contains the
+unique message id that is used by Exim to identify the message.
+An id is not created for a message until after its header has been
+successfully received.
+.em
+\**Note**\: This is \*not*\ the contents of the ::Message-ID:: header line; it
+is the local id that Exim assigns to the message, for example:
+\"1BXTIK-0001yO-VA"\.
+.nem
+
+.index size||of message
+.index message||size
+.tempindent 0
+\$message@_size$\:
+When a message is being processed, this variable contains its size in bytes. In
+most cases, the size includes those headers that were received with the
+message, but not those (such as ::Envelope-to::) that are added to individual
+deliveries as they are written. However, there is one special case: during the
+expansion of the \maildir@_tag\ option in the \%appendfile%\ transport while
+doing a delivery in maildir format, the value of \$message@_size$\ is the
+precise size of the file that has been written. See also
+\$message@_body@_size$\ and \$body@_linecount$\.
+
+.index \\RCPT\\||value of \$message@_size$\
+While running an ACL at the time of an SMTP \\RCPT\\ command, \$message@_size$\
+contains the size supplied on the \\MAIL\\ command, or
+-1
+if no size was given. The value may not, of course, be truthful.
+
+.tempindent 0
+\$n0$\ -- \$n9$\: These variables are counters that can be incremented by means
+of the \add\ command in filter files.
+
+.tempindent 0
+\$original@_domain$\: When a top-level address is being processed for delivery,
+this contains the same value as \$domain$\. However, if a `child' address (for
+example, generated by an alias, forward, or filter file) is being processed,
+this variable contains the domain of the original address. This differs from
+\$parent@_domain$\ only when there is more than one level of aliasing or
+forwarding. When more than one address is being delivered in a single transport
+run, \$original@_domain$\ is not set.
+
+If new an address is created by means of a \deliver\ command in a system
+filter, it is set up with an artificial `parent' address. This has the local
+part \*system-filter*\ and the default qualify domain.
+
+.tempindent 0
+\$original@_local@_part$\: When a top-level address is being processed for
+delivery, this contains the same value as \$local@_part$\, unless a prefix or
+suffix was removed from the local part, in which case \$original@_local@_part$\
+contains the full local part. When a `child' address (for example, generated by
+an alias, forward, or filter file) is being processed, this variable contains
+the full local part of the original address. If the router that did the
+redirection processed the local part case-insensitively, the value in
+\$original@_local@_part$\ is in lower case. This variable differs from
+\$parent@_local@_part$\ only when there is more than one level of aliasing or
+forwarding. When more than one address is being delivered in a single transport
+run, \$original@_local@_part$\ is not set.
+
+If new an address is created by means of a \deliver\ command in a system
+filter, it is set up with an artificial `parent' address. This has the local
+part \*system-filter*\ and the default qualify domain.
+
+
+.index gid (group id)||of originating user
+.index sender||gid
+.tempindent 0
+\$originator@_gid$\: The value of \$caller@_gid$\ that was set when the message
+was received. For messages received via the command line, this is the gid of
+the sending user. For messages received by SMTP over TCP/IP, this is normally
+the gid of the Exim user.
+
+.index uid (user id)||of originating user
+.index sender||uid
+.tempindent 0
+\$originator@_uid$\: The value of \$caller@_uid$\ that was set when the message
+was received. For messages received via the command line, this is the uid of
+the sending user. For messages received by SMTP over TCP/IP, this is normally
+the uid of the Exim user.
+
+.tempindent 0
+\$parent@_domain$\: This variable is similar to \$original@_domain$\ (see
+above), except that it refers to the immediately preceding parent address.
+
+.tempindent 0
+\$parent@_local@_part$\: This variable is similar to \$original@_local@_part$\
+(see above), except that it refers to the immediately preceding parent address.
+
+.index pid (process id)||of current process
+.tempindent 0
+\$pid$\: This variable contains the current process id.
+
+.index filter||transport filter
+.index transport||filter
+.tempindent 0
+\$pipe@_addresses$\: This is not an expansion variable, but is mentioned here
+because the string `@$pipe@_addresses' is handled specially in the command
+specification for the \%pipe%\ transport (chapter ~~CHAPpipetransport) and in
+transport filters (described under \transport@_filter\ in chapter
+~~CHAPtransportgeneric). It cannot be used in general expansion strings, and
+provokes an `unknown variable' error if encountered.
+
+.tempindent 0
+\$primary@_hostname$\: The value set in the configuration file, or read by the
+\*uname()*\ function. If \*uname()*\ returns a single-component name, Exim
+calls \*gethostbyname()*\ (or \*getipnodebyname()*\ where available) in an
+attempt to acquire a fully qualified host name.
+.em
+See also \$smtp@_active@_hostname$\.
+.nem
+
+.tempindent 0
+\$qualify@_domain$\: The value set for this option in the configuration file.
+
+.tempindent 0
+\$qualify@_recipient$\: The value set for this option in the configuration file,
+or if not set, the value of \$qualify@_domain$\.
+
+.tempindent 0
+\$rcpt@_count$\: When a message is being received by SMTP, this variable
+contains the number of \\RCPT\\ commands received for the current message. If
+this variable is used in a \\RCPT\\ ACL, its value includes the current
+command.
+
+.tempindent 0
+\$rcpt@_defer@_count$\: When a message is being received by SMTP, this variable
+contains the number of \\RCPT\\ commands in the current message that have
+previously been rejected with a temporary (4\*xx*\) response.
+
+.tempindent 0
+\$rcpt@_fail@_count$\: When a message is being received by SMTP, this variable
+contains the number of \\RCPT\\ commands in the current message that have
+previously been rejected with a permanent (5\*xx*\) response.
+
+.tempindent 0
+\$received@_count$\: This variable contains the number of ::Received:: header
+lines in the message, including the one added by Exim (so its value is always
+greater than zero). It is available in the \\DATA\\ ACL, the non-SMTP ACL, and
+while routing and delivering.
+
+.tempindent 0
+\$received@_for$\: If there is only a single recipient address in an incoming
+message, this variable contains that address when the ::Received:: header line
+is being built.
+.em
+The value is copied after recipient rewriting has happened, but before the
+\*local@_scan()*\ function is run.
+.nem
+
+.tempindent 0
+\$received@_protocol$\: When a message is being processed, this variable
+contains the name of the protocol by which it was received. See also the
+\-oMr-\ option.
+
+.em
+.tempindent 0
+\$recipient@_data$\: This variable is set after an indexing lookup success in
+an ACL \recipients\ condition. It contains the data from the lookup, and the
+value remains set until the next \recipients\ test. Thus, you can do things
+like this:
+.display
+require recipients = cdb*@@;/some/file
+deny \*some further test involving*\ @$recipient@_data
+.endd
+\**Warning**\: This variable is set only when a lookup is used as an indexing
+method in the address list, using the semicolon syntax as in the example above.
+The variable is not set for a lookup that is used as part of the string
+expansion that all such lists undergo before being interpreted.
+.nem
+
+.tempindent 0
+\$recipients$\: This variable contains a list of envelope recipients for a
+message. A comma and a space separate the addresses in the replacement text.
+However, the variable is not generally available, to prevent exposure of Bcc
+recipients in unprivileged users' filter files. You can use \$recipients$\ only
+.numberpars
+In a system filter file.
+.nextp
+In the \\DATA\\ or non-SMTP ACL, that is, in the final ACL for accepting a
+message.
+.endp
+
+.tempindent 0
+\$recipients@_count$\: When a message is being processed, this variable
+contains the number of envelope recipients that came with the message.
+Duplicates are not excluded from the count. While a message is being received
+over SMTP, the number increases for each accepted recipient. It can be
+referenced in an ACL.
+
+.tempindent 0
+\$reply@_address$\: When a message is being processed, this variable contains
+the contents of the ::Reply-To:: header line if one exists
+and it is not empty,
+or otherwise the contents of the ::From:: header line.
+
+.tempindent 0
+\$return@_path$\: When a message is being delivered, this variable contains the
+return path -- the sender field that will be sent as part of the envelope. It
+is not enclosed in @<@> characters.
+At the start of routing an address,
+\$return@_path$\ has the same value as \$sender@_address$\, but if, for
+example, an incoming message to a mailing list has been expanded by a router
+which specifies a different address for bounce messages, \$return@_path$\
+subsequently contains the new bounce address, whereas \$sender@_address$\
+always contains the original sender address that was received with the message.
+In other words, \$sender@_address$\ contains the incoming envelope sender, and
+\$return@_path$\ contains the outgoing envelope sender.
+
+.tempindent 0
+\$return@_size@_limit$\: This is an obsolete name for
+\$bounce@_return@_size@_limit$\.
+
+.index return code||from \run\ expansion
+.tempindent 0
+\$runrc$\: This variable contains the return code from a command that is run by
+the \@$@{run...@}\ expansion item.
+\**Warning**\: In a router or transport, you cannot assume the order in which
+option values are expanded, except for those pre-conditions whose order of
+testing is documented. Therefore, you cannot reliably expect to set \$runrc$\
+by the expansion of one option, and use it in another.
+
+.tempindent 0
+\$self@_hostname$\: When an address is routed to a supposedly remote host that
+turns out to be the local host, what happens is controlled by the
+.index \self\ option||value of host name
+\self\ generic router option. One of its values causes the address to be passed
+to another router. When this happens, \$self@_hostname$\ is set to the name of
+the local host that the original router encountered. In other circumstances its
+contents are null.
+
+.tempindent 0
+\$sender@_address$\: When a message is being processed, this variable contains
+the sender's address that was received in the message's envelope. For bounce
+messages, the value of this variable is the empty string.
+See also \$return@_path$\.
+
+.tempindent 0
+\$sender@_address@_domain$\: The domain portion of \$sender@_address$\.
+
+.tempindent 0
+\$sender@_address@_local@_part$\: The local part portion of \$sender@_address$\.
+
+.em
+.tempindent 0
+\$sender@_data$\: This variable is set after a lookup success in an ACL
+\senders\ condition or in a router \senders\ option. It contains the data from
+the lookup, and the value remains set until the next \senders\ test. Thus, you
+can do things like this:
+.display
+require senders = cdb*@@;/some/file
+deny \*some further test involving*\ @$sender@_data
+.endd
+\**Warning**\: This variable is set only when a lookup is used as an indexing
+method in the address list, using the semicolon syntax as in the example above.
+The variable is not set for a lookup that is used as part of the string
+expansion that all such lists undergo before being interpreted.
+.nem
+
+.tempindent 0
+\$sender@_fullhost$\: When a message is received from a remote host, this
+variable contains the host name and IP address in a single string. It ends
+with the IP address in square brackets, followed by a colon and a port number
+if the logging of ports is enabled. The format of the rest of the string
+depends on whether the host issued a \\HELO\\ or \\EHLO\\ SMTP command, and
+whether the host name was verified by looking up its IP address. (Looking up
+the IP address can be forced by the \host@_lookup\ option, independent of
+verification.) A plain host name at the start of the string is a verified host
+name; if this is not present, verification either failed or was not requested.
+A host name in parentheses is the argument of a \\HELO\\ or \\EHLO\\ command.
+This is omitted if it is identical to the verified host name or to the host's
+IP address in square brackets.
+
+.tempindent 0
+\$sender@_helo@_name$\: When a message is received from a remote host that has
+issued a \\HELO\\ or \\EHLO\\ command, the argument of that command is placed
+in this variable. It is also set if \\HELO\\ or \\EHLO\\ is used when a message
+is received using SMTP locally via the \-bs-\ or \-bS-\ options.
+
+.tempindent 0
+\$sender@_host@_address$\: When a message is received from a remote host, this
+variable contains that host's IP address. For locally submitted messages, it is
+empty.
+
+.tempindent 0
+\$sender@_host@_authenticated$\: This variable contains the name (not the
+public name) of the authenticator driver which successfully authenticated the
+client from which the message was received. It is empty if there was no
+successful authentication.
+
+.tempindent 0
+\$sender@_host@_name$\: When a message is received from a remote host, this
+variable contains the host's name as obtained by looking up its IP address.
+For messages received by other means, this variable is empty.
+
+If the host name has not previously been looked up, a reference to
+\$sender@_host@_name$\ triggers a lookup (for messages from remote hosts).
+.em
+A looked up name is accepted only if it leads back to the original IP address
+via a forward lookup. If either the reverse or the forward lookup fails, or if
+the forward lookup does not yield the original IP address,
+\$sender@_host@_name$\ remains empty, and \$host@_lookup@_failed$\ is set to
+`1'.
+.nem
+
+Exim does not automatically look up every calling host's name. If you want
+maximum efficiency, you should arrange your configuration so that it avoids
+these lookups altogether. The lookup happens only if one or more of the
+following are true:
+.numberpars
+A string containing \$sender@_host@_name$\ is expanded.
+.nextp
+The calling host matches the list in \host@_lookup\. In the default
+configuration, this option is set to $*$, so it must be changed if lookups are
+to be avoided. (In the code, the default for \host@_lookup\ is unset.)
+.nextp
+Exim needs the host name in order to test an item in a host list. The items
+that require this are described in sections ~~SECThoslispatnam and
+~~SECThoslispatnamsk.
+.nextp
+The calling host matches \helo@_try@_verify@_hosts\ or \helo@_verify@_hosts\.
+In this case, the host name is required to compare with the name quoted in any
+\\EHLO\\ or \\HELO\\ commands that the client issues.
+.nextp
+The remote host issues a \\EHLO\\ or \\HELO\\ command that quotes one of the
+domains in \helo@_lookup@_domains\. The default value of this option is
+.display asis
+helo_lookup_domains = @ : @[]
+.endd
+which causes a lookup if a remote host (incorrectly) gives the server's name or
+IP address in an \\EHLO\\ or \\HELO\\ command.
+.endp
+
+.tempindent 0
+\$sender@_host@_port$\: When a message is received from a remote host, this
+variable contains the port number that was used on the remote host.
+
+.tempindent 0
+\$sender@_ident$\: When a message is received from a remote host, this variable
+contains the identification received in response to an RFC 1413 request. When a
+message has been received locally, this variable contains the login name of the
+user that called Exim.
+
+.tempindent 0
+\$sender@_rcvhost$\: This is provided specifically for use in ::Received::
+headers. It starts with either the verified host name (as obtained from a
+.index DNS||reverse lookup
+.index reverse DNS lookup
+reverse DNS lookup) or, if there is no verified host name, the IP address in
+square brackets. After that there may be text in parentheses. When the first
+item is a verified host name, the first thing in the parentheses is the IP
+address in square brackets, followed by a colon and a port number if port
+logging is enabled. When the first item is an IP address, the port is recorded
+as `port=$it{xxxx}' inside the parentheses.
+
+There may also be items of the form `helo=$it{xxxx}' if \\HELO\\ or \\EHLO\\
+was used and its argument was not identical to the real host name or IP
+address, and `ident=$it{xxxx}' if an RFC 1413 ident string is available. If all
+three items are present in the parentheses, a newline and tab are inserted into
+the string, to improve the formatting of the ::Received:: header.
+
+.index \\AUTH\\||argument
+.index \\EXPN\\||argument
+.index \\ETRN\\||argument
+.index \\VRFY\\||argument
+.tempindent 0
+\$smtp@_command@_argument$\: While an ACL is running to check an \\AUTH\\,
+\\EHLO\\, \\EXPN\\, \\ETRN\\, \\HELO\\, or \\VRFY\\ command, this variable
+contains the argument for the SMTP command.
+
+.tempindent 0
+\$sn0$\ -- \$sn9$\: These variables are copies of the values of the \$n0$\
+-- \$n9$\ accumulators that were current at the end of the system filter file.
+This allows a system filter file to set values that can be tested in users'
+filter files. For example, a system filter could set a value indicating how
+likely it is that a message is junk mail.
+
+.tempindent 0
+\$spool@_directory$\: The name of Exim's spool directory.
+
+.tempindent 0
+\$thisaddress$\: This variable is set only during the processing of the
+\foranyaddress\ command in a filter file. Its use is explained in the
+description of that command.
+
+.tempindent 0
+\$tls@_certificate@_verified$\:
+This variable is set to `1' if a TLS certificate was verified when the message
+was received, and `0' otherwise.
+
+.tempindent 0
+\$tls@_cipher$\: When a message is received from a remote host over an
+encrypted SMTP connection, this variable is set to the cipher suite that was
+negotiated, for example DES-CBC3-SHA.
+In other circumstances, in particular, for message received over unencrypted
+connections, the variable is empty.
+See chapter ~~CHAPTLS for details of TLS support.
+
+.tempindent 0
+\$tls@_peerdn$\: When a message is received from a remote host over an
+encrypted SMTP connection,
+and Exim is configured to request a certificate from the client,
+the value of the Distinguished Name of the certificate is made available in the
+\$tls@_peerdn$\ during subsequent processing.
+
+.tempindent 0
+\$tod@_bsdinbox$\: The time of day and date, in the format required for
+BSD-style mailbox files, for example: Thu Oct 17 17:14:09 1995.
+
+.tempindent 0
+\$tod@_epoch$\: The time and date as a number of seconds since the start of the
+Unix epoch.
+
+.tempindent 0
+\$tod@_full$\: A full version of the time and date, for example: Wed, 16 Oct
+1995 09:51:40 +0100. The timezone is always given as a numerical offset from
+UTC, with positive values used for timezones that are ahead (east) of UTC, and
+negative values for those that are behind (west).
+
+.tempindent 0
+\$tod@_log$\: The time and date in the format used for writing Exim's log
+files, for example: 1995-10-12 15:32:29,
+but without a timezone.
+
+.tempindent 0
+\$tod@_logfile$\:
+This variable contains the date in the format yyyymmdd. This is the format that
+is used for datestamping log files when \log@_file@_path\ contains the \"%D"\
+flag.
+
+.tempindent 0
+\$tod@_zone$\: This variable contains the numerical value of the local
+timezone, for example: -0500.
+
+.tempindent 0
+\$tod@_zulu$\:
+This variable contains the UTC date and time in `Zulu' format, as specified by
+ISO 8601, for example: 20030221154023Z.
+
+.index \$value$\
+.tempindent 0
+\$value$\: This variable contains the result of an expansion lookup, extraction
+operation, or external command, as described above.
+
+.tempindent 0
+\$version@_number$\: The version number of Exim.
+
+.tempindent 0
+\$warn@_message@_delay$\: This variable is set only during the creation of a
+message warning about a delivery delay. Details of its use are explained in
+section ~~SECTcustwarn.
+
+.tempindent 0
+\$warn@_message@_recipients$\: This variable is set only during the creation of
+a message warning about a delivery delay. Details of its use are explained in
+section ~~SECTcustwarn.
+.pop
+
+
+
+.
+.
+. ============================================================================
+.chapter Embedded Perl
+.set runningfoot "embedded Perl"
+.rset CHAPperl "~~chapter"
+.index Perl||calling from Exim
+
+Exim can be built to include an embedded Perl interpreter. When this is done,
+Perl subroutines can be called as part of the string expansion process. To make
+use of the Perl support, you need version 5.004 or later of Perl installed on
+your system. To include the embedded interpreter in the Exim binary, include
+the line
+.display asis
+EXIM_PERL = perl.o
+.endd
+in your \(Local/Makefile)\ and then build Exim in the normal way.
+
+Access to Perl subroutines is via a global configuration option called
+.index \perl@_startup\
+\perl@_startup\ and an expansion string operator \@$@{perl ...@}\. If there is
+no \perl@_startup\ option in the Exim configuration file then no Perl
+interpreter is started and there is almost no overhead for Exim (since none of
+the Perl library will be paged in unless used). If there is a \perl@_startup\
+option then the associated value is taken to be Perl code which is executed in
+a newly created Perl interpreter.
+
+The value of \perl@_startup\ is not expanded in the Exim sense, so you do not
+need backslashes before any characters to escape special meanings. The option
+should usually be something like
+.display asis
+perl_startup = do '/etc/exim.pl'
+.endd
+where \(/etc/exim.pl)\ is Perl code which defines any subroutines you want to
+use from Exim. Exim can be configured either to start up a Perl interpreter as
+soon as it is entered, or to wait until the first time it is needed. Starting
+the interpreter at the beginning ensures that it is done while Exim still has
+its setuid privilege, but can impose an unnecessary overhead if Perl is not in
+fact used in a particular run. Also, note that this does not mean that Exim is
+necessarily running as root when Perl is called at a later time. By default,
+the interpreter is started only when it is needed, but this can be changed in
+two ways:
+.numberpars $.
+.index \perl@_at@_start\
+Setting \perl@_at@_start\ (a boolean option) in the configuration requests
+a startup when Exim is entered.
+.nextp
+The command line option \-ps-\ also requests a startup when Exim is entered,
+overriding the setting of \perl@_at@_start\.
+.endp
+There is also a command line option \-pd-\ (for delay) which suppresses the
+initial startup, even if \perl@_at@_start\ is set.
+
+When the configuration file includes a \perl@_startup\ option you can make use
+of the string expansion item to call the Perl subroutines that are defined
+by the \perl@_startup\ code. The operator is used in any of the following
+forms:
+.display asis
+${perl{foo}}
+${perl{foo}{argument}}
+${perl{foo}{argument1}{argument2} ... }
+.endd
+which calls the subroutine \foo\ with the given arguments. A maximum of eight
+arguments may be passed. Passing more than this results in an expansion failure
+with an error message of the form
+.display asis
+Too many arguments passed to Perl subroutine "foo" (max is 8)
+.endd
+The return value of the Perl subroutine is evaluated in a scalar context before
+it is passed back to Exim to be inserted into the expanded string. If the
+return value is \*undef*\, the expansion fails in the same way as an explicit
+`fail' on an \@$@{if ...@}\ or \@$@{lookup...@}\ item.
+If the subroutine aborts by obeying Perl's \die\ function, the expansion fails
+with the error message that was passed to \die\.
+
+Within any Perl code called from Exim, the function \*Exim@:@:expand@_string*\
+is available to call back into Exim's string expansion function. For example,
+the Perl code
+.display asis
+my $lp = Exim::expand_string('$local_part');
+.endd
+makes the current Exim \$local@_part$\ available in the Perl variable \$lp$\.
+Note those are single quotes and not double quotes to protect against
+\$local@_part$\ being interpolated as a Perl variable.
+
+If the string expansion is forced to fail by a `fail' item, the result of
+\*Exim@:@:expand@_string*\ is \undef\. If there is a syntax error in the
+expansion string, the Perl call from the original expansion string fails with
+an appropriate error message, in the same way as if \die\ were used.
+
+.index debugging||from embedded Perl
+.index log||writing from embedded Perl
+Two other Exim functions are available for use from within Perl code.
+\*Exim@:@:debug@_write(<<string>>)*\ writes the string to the standard error
+stream if Exim's debugging is enabled. If you want a newline at the end, you
+must supply it. \*Exim@:@:log@_write(<<string>>)*\ writes the string to Exim's
+main log, adding a leading timestamp. In this case, you should not supply a
+terminating newline.
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Starting the daemon and the use of network interfaces
+.set runningfoot "starting the daemon"
+.rset CHAPinterfaces "~~chapter"
+.index daemon||starting
+.index interface||listening
+.index network interface
+.index interface||network
+.index IP address||for listening
+.index daemon||listening IP addresses
+.index TCP/IP||setting listening interfaces
+.index TCP/IP||setting listening ports
+
+A host that is connected to a TCP/IP network may have one or more physical
+hardware network interfaces. Each of these interfaces may be configured as one
+or more `logical' interfaces, which are the entities that a program actually
+works with. Each of these logical interfaces is associated with an IP address.
+In addition, TCP/IP software supports `loopback' interfaces (127.0.0.1 in IPv4
+and @:@:1 in IPv6), which do not use any physical hardware. Exim requires
+knowledge about the host's interfaces for use in three different circumstances:
+.numberpars
+When a listening daemon is started, Exim needs to know which interfaces
+and ports to listen on.
+.nextp
+When Exim is routing an address, it needs to know which IP addresses
+are associated with local interfaces. This is required for the correct
+processing of MX lists by removing the local host and others with the
+same or higher priority values. Also, Exim needs to detect cases
+when an address is routed to an IP address that in fact belongs to the
+local host. Unless the \self\ router option or the \allow@_localhost\
+option of the smtp transport is set (as appropriate), this is treated
+as an error situation.
+.nextp
+When Exim connects to a remote host, it may need to know which interface to use
+for the outgoing connection.
+.endp
+
+Exim's default behaviour is likely to be appropriate in the vast majority
+of cases. If your host has only one interface, and you want all its IP
+addresses to be treated in the same way, and you are using only the
+standard SMTP port, you should not need to take any special action. The
+rest of this chapter does not apply to you.
+
+In a more complicated situation you may want to listen only on certain
+interfaces, or on different ports, and for this reason there are a number of
+options that can be used to influence Exim's behaviour. The rest of this
+chapter describes how they operate.
+
+When a message is received over TCP/IP, the interface and port that were
+actually used are set in \$interface@_address$\ and \$interface@_port$\.
+
+
+.section Starting a listening daemon
+When a listening daemon is started (by means of the \-bd-\ command line
+option), the interfaces and ports on which it listens are controlled by the
+following options:
+.numberpars $.
+\daemon@_smtp@_ports\ contains a list of default ports. (For backward
+compatibility, this option can also be specified in the singular.)
+.nextp
+\local@_interfaces\ contains list of interface IP addresses on which to
+listen. Each item may optionally also specify a port.
+.endp
+The default list separator in both cases is a colon, but this can be changed as
+described in section ~~SECTlistconstruct. When IPv6 addresses are involved, it
+is usually best to change the separator to avoid having to double all the
+colons. For example:
+.display asis
+local_interfaces = <; 127.0.0.1 ; \
+ 192.168.23.65 ; \
+ ::1 ; \
+ 3ffe:ffff:836f::fe86:a061
+.endd
+There are two different formats for specifying a port along with an IP address
+in \local@_interfaces\:
+.numberpars
+The port is added onto the address with a dot separator. For example, to listen
+on port 1234 on two different IP addresses:
+.display asis
+local_interfaces = <; 192.168.23.65.1234 ; \
+ 3ffe:ffff:836f::fe86:a061.1234
+.endd
+.nextp
+The IP address is enclosed in square brackets, and the port is added
+with a colon separator, for example:
+.display asis
+local_interfaces = <; [192.168.23.65]:1234 ; \
+ [3ffe:ffff:836f::fe86:a061]:1234
+.endd
+.endp
+When a port is not specified, the value of \daemon@_smtp@_ports\ is used. The
+default setting contains just one port:
+.display asis
+daemon_smtp_ports = smtp
+.endd
+If more than one port is listed, each interface that does not have its own port
+specified listens on all of them. Ports that are listed in
+\daemon@_smtp@_ports\ can be identified either by name (defined in
+\(/etc/services)\) or by number. However, when ports are given with individual
+IP addresses in \local@_interfaces\, only numbers (not names) can be used.
+
+
+.section Special IP listening addresses
+The addresses 0.0.0.0 and @:@:0 are treated specially. They are interpreted
+as `all IPv4 interfaces' and `all IPv6 interfaces', respectively. In each
+case, Exim tells the TCP/IP stack to `listen on all IPv\*x*\ interfaces'
+instead of setting up separate listening sockets for each interface. The
+default value of \local@_interfaces\ is
+.display asis
+local_interfaces = 0.0.0.0
+.endd
+when Exim is built without IPv6 support; otherwise it is:
+.display asis
+local_interfaces = <; ::0 ; 0.0.0.0
+.endd
+Thus, by default, Exim listens on all available interfaces, on the SMTP port.
+
+
+.section Overriding local@_interfaces and daemon@_smtp@_ports
+The \-oX-\ command line option can be used to override the values of
+\daemon@_smtp@_ports\ and/or \local@_interfaces\ for a particular daemon
+instance. Another way of doing this would be to use macros and the \-D-\
+option. However, \-oX-\ can be used by any admin user, whereas modification of
+the runtime configuration by \-D-\ is allowed only when the caller is root or
+exim.
+
+The value of \-oX-\ is a list of items. The default colon separator can be
+changed in the usual way if required. If there are any items that do not
+contain dots or colons (that is, are not IP addresses), the value of
+\daemon@_smtp@_ports\ is replaced by the list of those items. If there are any
+items that do contain dots or colons, the value of \local@_interfaces\ is
+replaced by those items. Thus, for example,
+.display asis
+-oX 1225
+.endd
+overrides \daemon@_smtp@_ports\, but leaves \local@_interfaces\ unchanged,
+whereas
+.display asis
+-oX 192.168.34.5.1125
+.endd
+overrides \local@_interfaces\, leaving \daemon@_smtp@_ports\ unchanged.
+(However, since \local@_interfaces\ now contains no items without ports, the
+value of \daemon@_smtp@_ports\ is no longer relevant in this example.)
+
+
+.section IPv6 address scopes
+IPv6 addresses have `scopes', and a host with multiple hardware interfaces
+can, in principle, have the same link-local IPv6 address on different
+interfaces. Thus, additional information is needed, over and above the IP
+address, to distinguish individual interfaces. A convention of using a
+percent sign followed by something (often the interface name) has been
+adopted in some cases, leading to addresses like this:
+.display asis
+3ffe:2101:12:1:a00:20ff:fe86:a061%eth0
+.endd
+To accommodate this usage, a percent sign followed by an arbitrary string is
+allowed at the end of an IPv6 address. By default, Exim calls \*getaddrinfo()*\
+to convert a textual IPv6 address for actual use. This function recognizes the
+percent convention in operating systems that support it, and it processes the
+address appropriately. Unfortunately, some older libraries have problems with
+\*getaddrinfo()*\. If
+.display asis
+IPV6_USE_INET_PTON=yes
+.endd
+is set in \(Local/Makefile)\ (or an OS-dependent Makefile) when Exim is built,
+Exim uses \*inet@_pton()*\ to convert a textual IPv6 address for actual use,
+instead of \*getaddrinfo()*\. (Before version 4.14, it always used this
+function.) Of course, this means that the additional functionality of
+\*getaddrinfo()*\ -- recognizing scoped addresses -- is lost.
+
+
+.section Examples of starting a listening daemon
+The default case in an IPv6 environment is
+.display asis
+daemon_smtp_port = smtp
+local_interfaces = <; ::0 ; 0.0.0.0
+.endd
+This specifies listening on the smtp port on all IPv6 and IPv4 interfaces.
+Either one or two sockets may be used, depending on the characteristics of
+the TCP/IP stack. (This is complicated and messy; for more information,
+read the comments in the \(daemon.c)\ source file.)
+
+To specify listening on ports 25 and 26 on all interfaces:
+.display asis
+daemon_smtp_ports = 25 : 26
+.endd
+(leaving \local@_interfaces\ at the default setting) or, more explicitly:
+.display asis
+local_interfaces = <; ::0.25 ; ::0.26 \
+ 0.0.0.0.25 ; 0.0.0.0.26
+.endd
+To listen on the default port on all IPv4 interfaces, and on port 26 on the
+IPv4 loopback address only:
+.display asis
+local_interfaces = 0.0.0.0 : 127.0.0.1.26
+.endd
+To specify listening on the default port on specific interfaces only:
+.display asis
+local_interfaces = 192.168.34.67 : 192.168.34.67
+.endd
+\**Note**\: such a setting excludes listening on the loopback interfaces.
+
+
+.section Recognising the local host
+.rset SECTreclocipadd "~~chapter.~~section"
+The \local@_interfaces\ option is also used when Exim needs to determine
+whether or not an IP address refers to the local host. That is, the IP
+addresses of all the interfaces on which a daemon is listening are always
+treated as local.
+
+For this usage, port numbers in \local@_interfaces\ are ignored. If either of
+the items 0.0.0.0 or @:@:0 are encountered, Exim gets a complete list of
+available interfaces from the operating system, and extracts the relevant
+(that is, IPv4 or IPv6) addresses to use for checking.
+
+Some systems set up large numbers of virtual interfaces in order to provide
+many virtual web servers. In this situation, you may want to listen for
+email on only a few of the available interfaces, but nevertheless treat all
+interfaces as local when routing. You can do this by setting
+\extra@_local@_interfaces\ to a list of IP addresses, possibly including the
+`all' wildcard values. These addresses are recognized as local, but are not
+used for listening. Consider this example:
+.display asis
+local_interfaces = <; 127.0.0.1 ; ::1 ; \
+ 192.168.53.235 ; \
+ 3ffe:2101:12:1:a00:20ff:fe86:a061
+
+extra_local_interfaces = <; ::0 ; 0.0.0.0
+.endd
+The daemon listens on the loopback interfaces and just one IPv4 and one IPv6
+address, but all available interface addresses are treated as local when
+Exim is routing.
+
+In some environments the local host name may be in an MX list, but with an IP
+address that is not assigned to any local interface. In other cases it may be
+desirable to treat other host names as if they referred to the local host. Both
+these cases can be handled by setting the \hosts@_treat@_as@_local\ option.
+This contains host names rather than IP addresses. When a host is referenced
+during routing, either via an MX record or directly, it is treated as the local
+host if its name matches \hosts@_treat@_as@_local\, or if any of its IP
+addresses match \local@_interfaces\ or \extra@_local@_interfaces\.
+
+
+.section Delivering to a remote host
+Delivery to a remote host is handled by the smtp transport. By default, it
+allows the system's TCP/IP functions to choose which interface to use (if
+there is more than one) when connecting to a remote host. However, the
+\interface\ option can be set to specify which interface is used. See the
+description of the smtp transport in chapter ~~CHAPsmtptrans for more details.
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Main configuration
+.set runningfoot "main configuration"
+.rset CHAPmainconfig "~~chapter"
+.index configuration file||main section
+.index main configuration
+The first part of the run time configuration file contains three types of item:
+.numberpars $.
+Macro definitions: These lines start with an upper case letter. See section
+~~SECTmacrodefs for details of macro processing.
+.nextp
+Named list definitions: These lines start with one of the words `domainlist',
+`hostlist', `addresslist', or `localpartlist'. Their use is described in
+section ~~SECTnamedlists.
+.nextp
+Main configuration settings: Each setting occupies one line of the file
+(with possible continuations). If any setting is preceded by the word
+`hide', the \-bP-\ command line option displays its value to admin users only.
+See section ~~SECTcos for a description of the syntax of these option settings.
+.endp
+This chapter specifies all the main configuration options, along with their
+types and default values. For ease of finding a particular option, they appear
+in alphabetical order in section ~~SECTalomo below. However, because there are
+now so many options, they are first listed briefly in functional groups, as an
+aid to finding the name of the option you are looking for.
+Some options are listed in more than one group.
+
+.set savedisplayflowcheck ~~displayflowcheck
+.set displayflowcheck 0
+
+.section Miscellaneous
+.display flow rm
+.tabs 31
+\bi@_command\ $t$rm{to run for \-bi-\ command line option}
+\keep@_malformed\ $t$rm{for broken files -- should not happen}
+\localhost@_number\ $t$rm{for unique message ids in clusters}
+\message@_body@_visible\ $t$rm{how much to show in \$message@_body$\}
+\print@_topbitchars\ $t$rm{top-bit characters are printing}
+\timezone\ $t$rm{force time zone}
+.endd
+
+.section Exim parameters
+.display flow rm
+.tabs 31
+\exim@_group\ $t$rm{override compiled-in value}
+\exim@_path\ $t$rm{override compiled-in value}
+\exim@_user\ $t$rm{override compiled-in value}
+\primary@_hostname\ $t$rm{default from \*uname()*\}
+\split@_spool@_directory\ $t$rm{use multiple directories}
+\spool@_directory\ $t$rm{override compiled-in value}
+.endd
+
+.section Privilege controls
+.display flow rm
+.tabs 31
+\admin@_groups\ $t$rm{groups that are Exim admin users}
+\deliver@_drop@_privilege\ $t$rm{drop root for delivery processes}
+\local@_from@_check\ $t$rm{insert ::Sender:: if necessary}
+\local@_from@_prefix\ $t$rm{for testing ::From:: for local sender}
+\local@_from@_suffix\ $t$rm{for testing ::From:: for local sender}
+\local@_sender@_retain\ $t$rm{keep ::Sender:: from untrusted user}
+\never@_users\ $t$rm{do not run deliveries as these}
+\prod@_requires@_admin\ $t$rm{forced delivery requires admin user}
+\queue@_list@_requires@_admin\ $t$rm{queue listing requires admin user}
+\trusted@_groups\ $t$rm{groups that are trusted}
+\trusted@_users\ $t$rm{users that are trusted}
+.endd
+
+.section Logging
+.display flow rm
+.tabs 31
+\log@_file@_path\ $t$rm{override compiled-in value}
+\log@_selector\ $t$rm{set/unset optional logging}
+\log@_timezone\ $t$rm{add timezone to log lines}
+\message@_logs\ $t$rm{create per-message logs}
+\preserve@_message@_logs\ $t$rm{in another directory after message completion}
+\process@_log@_path\ $t$rm{for SIGUSR1 and \*exiwhat*\}
+\syslog@_duplication\ $t$rm{controls duplicate log lines on syslog }
+\syslog@_facility\ $t$rm{set syslog `facility' field}
+\syslog@_processname\ $t$rm{set syslog `ident' field}
+\syslog@_timestamp\ $t$rm{timestamp syslog lines}
+.newline
+.em
+\write@_rejectlog\ $t$rm{control use of message log}
+.newline
+.nem
+.endd
+
+.section Frozen messages
+.display flow rm
+.tabs 31
+\auto@_thaw\ $t$rm{sets time for retrying frozen messages}
+\freeze@_tell\ $t$rm{send message when freezing}
+\move@_frozen@_messages\ $t$rm{to another directory}
+\timeout@_frozen@_after\ $t$rm{keep frozen messages only so long}
+.endd
+
+.section Data lookups
+.display flow rm
+.tabs 31
+\ldap@_default@_servers\ $t$rm{used if no server in query}
+\ldap@_version\ $t$rm{set protocol version}
+\lookup@_open@_max\ $t$rm{lookup files held open}
+\mysql@_servers\ $t$rm{as it says}
+\oracle@_servers\ $t$rm{as it says}
+\pgsql@_servers\ $t$rm{as it says}
+.endd
+
+.section Message ids
+.display flow rm
+.tabs 31
+\message@_id@_header@_domain\ $t$rm{used to build ::Message-ID:: header}
+\message@_id@_header@_text\ $t$rm{ditto}
+.endd
+
+.section Embedded Perl Startup
+.display flow rm
+.tabs 31
+\perl@_at@_start\ $t$rm{always start the interpreter}
+\perl@_startup\ $t$rm{code to obey when starting Perl}
+.endd
+
+.section Daemon
+.display flow rm
+.tabs 31
+\daemon@_smtp@_ports\ $t$rm{default ports}
+\extra@_local@_interfaces\ $t$rm{not necessarily listened on}
+\local@_interfaces\ $t$rm{on which to listen, with optional ports}
+\pid@_file@_path\ $t$rm{override compiled-in value}
+\queue@_run@_max\ $t$rm{maximum number of simultaneous queue runners}
+.endd
+
+.section Resource control
+.display flow rm
+.tabs 31
+\check@_log@_inodes\ $t$rm{before accepting a message}
+\check@_log@_space\ $t$rm{before accepting a message}
+\check@_spool@_inodes\ $t$rm{before accepting a message}
+\check@_spool@_space\ $t$rm{before accepting a message}
+\deliver@_queue@_load@_max\ $t$rm{no queue deliveries if load high}
+\queue@_only@_load\ $t$rm{queue incoming if load high}
+\queue@_run@_max\ $t$rm{maximum number of simultaneous queue runners}
+\remote@_max@_parallel\ $t$rm{parallel SMTP delivery per message}
+\smtp@_accept@_max\ $t$rm{simultaneous incoming connections}
+\smtp@_accept@_max@_nommail\ $t$rm{non-mail commands}
+\smtp@_accept@_max@_nonmail@_hosts\ $t$rm{hosts to which the limit applies}
+\smtp@_accept@_max@_per@_connection\ $t$rm{messages per connection}
+\smtp@_accept@_max@_per@_host\ $t$rm{connections from one host}
+\smtp@_accept@_queue\ $t$rm{queue mail if more connections}
+\smtp@_accept@_queue@_per@_connection\ $t$rm{queue if more messages per connection}
+\smtp@_accept@_reserve\ $t$rm{only reserve hosts if more connections}
+\smtp@_check@_spool@_space\ $t$rm{from \\SIZE\\ on \\MAIL\\ command}
+\smtp@_connect@_backlog\ $t$rm{passed to TCP/IP stack}
+\smtp@_load@_reserve\ $t$rm{SMTP from reserved hosts if load high}
+\smtp@_reserve@_hosts\ $t$rm{these are the reserve hosts}
+.endd
+
+.section Policy controls
+.display flow rm
+.tabs 31
+\acl@_not@_smtp\ $t$rm{set ACL for non-SMTP messages}
+\acl@_smtp@_auth\ $t$rm{set ACL for \\AUTH\\}
+\acl@_smtp@_connect\ $t$rm{set ACL for connection}
+\acl@_smtp@_data\ $t$rm{set ACL for \\DATA\\}
+\acl@_smtp@_etrn\ $t$rm{set ACL for \\ETRN\\}
+\acl@_smtp@_expn\ $t$rm{set ACL for \\EXPN\\}
+\acl@_smtp@_helo\ $t$rm{set ACL for \\EHLO\\ or \\HELO\\}
+\acl@_smtp@_mail\ $t$rm{set ACL for \\MAIL\\}
+\acl@_smtp@_mailauth\ $t$rm{set ACL for \\AUTH\\ on \\MAIL\\ command}
+\acl@_smtp@_rcpt\ $t$rm{set ACL for \\RCPT\\}
+\acl@_smtp@_starttls\ $t$rm{set ACL for \\STARTTLS\\}
+\acl@_smtp@_vrfy\ $t$rm{set ACL for \\VRFY\\}
+\header@_maxsize\ $t$rm{total size of message header}
+\header@_line@_maxsize\ $t$rm{individual header line limit}
+\helo@_accept@_junk@_hosts\ $t$rm{allow syntactic junk from these hosts}
+\helo@_allow@_chars\ $t$rm{allow illegal chars in \\HELO\\ names}
+\helo@_lookup@_domains\ $t$rm{lookup hostname for these \\HELO\\ names}
+\helo@_try@_verify@_hosts\ $t$rm{\\HELO\\ soft-checked for these hosts}
+\helo@_verify@_hosts\ $t$rm{\\HELO\\ hard-checked for these hosts}
+\host@_lookup\ $t$rm{host name looked up for these hosts}
+\host@_lookup@_order\ $t$rm{order of DNS and local name lookups}
+\host@_reject@_connection\ $t$rm{reject connection from these hosts}
+\hosts@_treat@_as@_local\ $t$rm{useful in some cluster configurations}
+\local@_scan@_timeout\ $t$rm{timeout for \*local@_scan()*\}
+\message@_size@_limit\ $t$rm{for all messages}
+\percent@_hack@_domains\ $t$rm{recognize %-hack for these domains}
+.endd
+
+.section Callout cache
+.display flow rm
+.tabs 31
+\callout@_domain@_negative@_expire\ $t$rm{timeout for negative domain cache item}
+\callout@_domain@_positive@_expire\ $t$rm{timeout for positive domain cache item}
+\callout@_negative@_expire\ $t$rm{timeout for negative address cache item}
+\callout@_positive@_expire\ $t$rm{timeout for positive address cache item}
+\callout@_random@_local@_part\ $t$rm{string to use for `random' testing}
+.endd
+
+.section TLS
+.display flow rm
+.tabs 31
+\tls@_advertise@_hosts\ $t$rm{advertise TLS to these hosts}
+\tls@_certificate\ $t$rm{location of server certificate}
+.newline
+.em
+\tls@_crl\ $t$rm{certificate revocation list}
+.newline
+.nem
+\tls@_dhparam\ $t$rm{DH parameters for server}
+\tls@_privatekey\ $t$rm{location of server private key}
+\tls@_remember@_esmtp\ $t$rm{don't reset after starting TLS}
+.newline
+.em
+\tls@_require@_ciphers\ $t$rm{specify acceptable cipers}
+.newline
+.nem
+\tls@_try@_verify@_hosts\ $t$rm{try to verify client certificate}
+\tls@_verify@_certificates\ $t$rm{expected client certificates}
+\tls@_verify@_hosts\ $t$rm{insist on client certificate verify}
+.endd
+
+.section Local user handling
+.display flow rm
+.tabs 31
+\finduser@_retries\ $t$rm{useful in NIS environments}
+\gecos@_name\ $t$rm{used when creating ::Sender::}
+\gecos@_pattern\ $t$rm{ditto}
+\max@_username@_length\ $t$rm{for systems that truncate}
+\unknown@_login\ $t$rm{used when no login name found}
+\unknown@_username\ $t$rm{ditto}
+\uucp@_from@_pattern\ $t$rm{for recognizing `From ' lines}
+\uucp@_from@_sender\ $t$rm{ditto}
+.endd
+
+.section All incoming messages (SMTP and non-SMTP)
+.display flow rm
+.tabs 31
+\header@_maxsize\ $t$rm{total size of message header}
+\header@_line@_maxsize\ $t$rm{individual header line limit}
+\message@_size@_limit\ $t$rm{applies to all messages}
+\percent@_hack@_domains\ $t$rm{recognize %-hack for these domains}
+\received@_header@_text\ $t$rm{expanded to make ::Received::}
+\received@_headers@_max\ $t$rm{for mail loop detection}
+\recipients@_max\ $t$rm{limit per message}
+\recipients@_max@_reject\ $t$rm{permanently reject excess}
+.endd
+
+
+.section Non-SMTP incoming messages
+.display rm
+.tabs 31
+\receive@_timeout\ $t$rm{for non-SMTP messages}
+.endd
+
+
+
+.section Incoming SMTP messages
+See also the \*Policy controls*\ section above.
+.display flow rm
+.tabs 31
+\host@_lookup\ $t$rm{host name looked up for these hosts}
+\host@_lookup@_order\ $t$rm{order of DNS and local name lookups}
+\recipient@_unqualified@_hosts\ $t$rm{may send unqualified recipients}
+\rfc1413@_hosts\ $t$rm{make ident calls to these hosts}
+\rfc1413@_query@_timeout\ $t$rm{zero disables ident calls}
+\sender@_unqualified@_hosts\ $t$rm{may send unqualified senders}
+\smtp@_accept@_keepalive\ $t$rm{some TCP/IP magic}
+\smtp@_accept@_max\ $t$rm{simultaneous incoming connections}
+\smtp@_accept@_max@_nommail\ $t$rm{non-mail commands}
+\smtp@_accept@_max@_nonmail@_hosts\ $t$rm{hosts to which the limit applies}
+\smtp@_accept@_max@_per@_connection\ $t$rm{messages per connection}
+\smtp@_accept@_max@_per@_host\ $t$rm{connections from one host}
+\smtp@_accept@_queue\ $t$rm{queue mail if more connections}
+\smtp@_accept@_queue@_per@_connection\ $t$rm{queue if more messages per connection}
+\smtp@_accept@_reserve\ $t$rm{only reserve hosts if more connections}
+.newline
+.em
+\smtp@_active@_hostname\ $t$rm{host name to use in messages}
+.newline
+.nem
+\smtp@_banner\ $t$rm{text for welcome banner}
+\smtp@_check@_spool@_space\ $t$rm{from \\SIZE\\ on \\MAIL\\ command}
+\smtp@_connect@_backlog\ $t$rm{passed to TCP/IP stack}
+\smtp@_enforce@_sync\ $t$rm{of SMTP command/responses}
+\smtp@_etrn@_command\ $t$rm{what to run for \\ETRN\\}
+\smtp@_etrn@_serialize\ $t$rm{only one at once}
+\smtp@_load@_reserve\ $t$rm{only reserve hosts if this load}
+\smtp@_max@_unknown@_commands\ $t$rm{before dropping connection}
+\smtp@_ratelimit@_hosts\ $t$rm{apply ratelimiting to these hosts}
+\smtp@_ratelimit@_mail\ $t$rm{ratelimit for \\MAIL\\ commands}
+\smtp@_ratelimit@_rcpt\ $t$rm{ratelimit for \\RCPT\\ commands}
+\smtp@_receive@_timeout\ $t$rm{per command or data line}
+\smtp@_reserve@_hosts\ $t$rm{these are the reserve hosts}
+\smtp@_return@_error@_details\ $t$rm{give detail on rejections}
+.endd
+
+.section SMTP extensions
+.display flow rm
+.tabs 31
+\accept@_8bitmime\ $t$rm{advertise \\8BITMIME\\}
+\auth@_advertise@_hosts\ $t$rm{advertise \\AUTH\\ to these hosts}
+\ignore@_fromline@_hosts\ $t$rm{allow `From ' from these hosts}
+\ignore@_fromline@_local\ $t$rm{allow `From ' from local SMTP}
+\pipelining@_advertise@_hosts\ $t$rm{advertise pipelining to these hosts}
+\tls@_advertise@_hosts\ $t$rm{advertise TLS to these hosts}
+.endd
+
+.section Processing messages
+.display flow rm
+.tabs 31
+\allow@_domain@_literals\ $t$rm{recognize domain literal syntax}
+\allow@_mx@_to@_ip\ $t$rm{allow MX to point to IP address}
+\allow@_utf8@_domains\ $t$rm{in addresses}
+\delivery@_date@_remove\ $t$rm{from incoming messages}
+\envelope@_to@_remote\ $t$rm{from incoming messages}
+\extract@_addresses@_remove@_arguments\ $t$rm{affects \-t-\ processing}
+\headers@_charset\ $t$rm{default for translations}
+\qualify@_domain\ $t$rm{default for senders}
+\qualify@_recipient\ $t$rm{default for recipients}
+\return@_path@_remove\ $t$rm{from incoming messages}
+\strip@_excess@_angle@_brackets\ $t$rm{in addresses}
+\strip@_trailing@_dot\ $t$rm{at end of addresses}
+\untrusted@_set@_sender\ $t$rm{untrusted can set envelope sender}
+.endd
+
+.section System filter
+.display flow rm
+.tabs 31
+\system@_filter\ $t$rm{locate system filter}
+\system@_filter@_directory@_transport\ $t$rm{transport for delivery to a directory}
+\system@_filter@_file@_transport\ $t$rm{transport for delivery to a file}
+\system@_filter@_group\ $t$rm{group for filter running}
+\system@_filter@_pipe@_transport\ $t$rm{transport for delivery to a pipe}
+\system@_filter@_reply@_transport\ $t$rm{transport for autoreply delivery}
+\system@_filter@_user\ $t$rm{user for filter running}
+.endd
+
+.section Routing and delivery
+.display flow rm
+.tabs 31
+\dns@_again@_means@_nonexist\ $t$rm{for broken domains}
+\dns@_check@_names@_pattern\ $t$rm{pre-DNS syntax check}
+\dns@_ipv4@_lookup\ $t$rm{only v4 lookup for these domains}
+\dns@_retrans\ $t$rm{parameter for resolver}
+\dns@_retry\ $t$rm{parameter for resolver}
+\hold@_domains\ $t$rm{hold delivery for these domains}
+\local@_interfaces\ $t$rm{for routing checks}
+\queue@_domains\ $t$rm{no immediate delivery for these}
+\queue@_only\ $t$rm{no immediate delivery at all}
+\queue@_only@_file\ $t$rm{no immediate deliveryif file exists}
+\queue@_only@_load\ $t$rm{no immediate delivery if load is high}
+\queue@_only@_override\ $t$rm{allow command line to override}
+\queue@_run@_in@_order\ $t$rm{order of arrival}
+\queue@_run@_max\ $t$rm{of simultaneous queue runners}
+\queue@_smtp@_domains\ $t$rm{no immediate SMTP delivery for these}
+\remote@_max@_parallel\ $t$rm{parallel SMTP delivery (per message, not overall)}
+\remote@_sort@_domains\ $t$rm{order of remote deliveries}
+\retry@_data@_expire\ $t$rm{timeout for retry data}
+\retry@_interval@_max\ $t$rm{safety net for retry rules}
+.endd
+
+.section Bounce and warning messages
+.display flow rm
+.tabs 31
+\bounce@_message@_file\ $t$rm{content of bounce}
+\bounce@_message@_text\ $t$rm{content of bounce}
+\bounce@_return@_body\ $t$rm{include body if returning message}
+\bounce@_return@_message\ $t$rm{include original message in bounce}
+\bounce@_return@_size@_limit\ $t$rm{limit on returned message}
+\bounce@_sender@_authentication\ $t$rm{send authenticated sender with bounce}
+\errors@_copy\ $t$rm{copy bounce messages}
+\errors@_reply@_to\ $t$rm{::Reply-to:: in bounces}
+\delay@_warning\ $t$rm{time schedule}
+\delay@_warning@_condition\ $t$rm{condition for warning messages}
+\ignore@_bounce@_errors@_after\ $t$rm{discard undeliverable bounces}
+\warn@_message@_file\ $t$rm{content of warning message}
+.endd
+
+.set displayflowcheck ~~savedisplayflowcheck
+
+.section Alphabetical list of main options
+.rset SECTalomo "~~chapter.~~section"
+.if ~~sgcal
+Those options that undergo string expansion before use are marked with $**$.
+.fi
+
+.startconf
+
+.index \\8BITMIME\\
+.index 8-bit characters
+.conf accept@_8bitmime boolean false
+This option causes Exim to send \\8BITMIME\\ in its response to an SMTP
+\\EHLO\\ command, and to accept the \\BODY=\\ parameter on \\MAIL\\ commands.
+However, though Exim is 8-bit clean, it is not a protocol converter, and it
+takes no steps to do anything special with messages received by this route.
+Consequently, this option is turned off by default.
+
+.index ~~ACL||for non-SMTP messages
+.index non-SMTP messages, ACL for
+.conf acl@_not@_smtp string$**$ unset
+This option defines the ACL that is run when a non-SMTP message is on the point
+of being accepted. See chapter ~~CHAPACL for further details.
+
+.index ~~ACL||on SMTP connection
+.conf acl@_smtp@_connect string$**$ unset
+This option defines the ACL that is run when an SMTP connection is received.
+See chapter ~~CHAPACL for further details.
+
+.index ~~ACL||setting up for SMTP commands
+.index \\AUTH\\||ACL for
+.conf acl@_smtp@_auth string$**$ unset
+This option defines the ACL that is run when an SMTP \\AUTH\\ command is
+received. See chapter ~~CHAPACL for further details.
+
+.index \\DATA\\, ACL for
+.conf acl@_smtp@_data string$**$ unset
+This option defines the ACL that is run after an SMTP \\DATA\\ command has been
+processed and the message itself has been received, but before the final
+acknowledgement is sent. See chapter ~~CHAPACL for further details.
+
+.index \\ETRN\\||ACL for
+.conf acl@_smtp@_etrn string$**$ unset
+This option defines the ACL that is run when an SMTP \\ETRN\\ command is
+received. See chapter ~~CHAPACL for further details.
+
+.index \\EXPN\\||ACL for
+.conf acl@_smtp@_expn string$**$ unset
+This option defines the ACL that is run when an SMTP \\EXPN\\ command is
+received. See chapter ~~CHAPACL for further details.
+
+.index \\EHLO\\||ACL for
+.index \\HELO\\||ACL for
+.conf acl@_smtp@_helo string$**$ unset
+This option defines the ACL that is run when an SMTP \\EHLO\\ or \\HELO\\
+command is received. See chapter ~~CHAPACL for further details.
+
+.index \\MAIL\\||ACL for
+.conf acl@_smtp@_mail string$**$ unset
+This option defines the ACL that is run when an SMTP \\MAIL\\ command is
+received. See chapter ~~CHAPACL for further details.
+
+.index \\AUTH\\||on \\MAIL\\ command
+.conf acl@_smtp@_mailauth string$**$ unset
+This option defines the ACL that is run when there is an \\AUTH\\ parameter on
+a \\MAIL\\ command. See chapter ~~CHAPACL for details of ACLs, and chapter
+~~CHAPSMTPAUTH for details of authentication.
+
+.index \\RCPT\\||ACL for
+.conf acl@_smtp@_rcpt string$**$ unset
+This option defines the ACL that is run when an SMTP \\RCPT\\ command is
+received. See chapter ~~CHAPACL for further details.
+
+.index \\STARTTLS\\, ACL for
+.conf acl@_smtp@_starttls string$**$ unset
+This option defines the ACL that is run when an SMTP \\STARTTLS\\ command is
+received. See chapter ~~CHAPACL for further details.
+
+.index \\VRFY\\||ACL for
+.conf acl@_smtp@_vrfy string$**$ unset
+This option defines the ACL that is run when an SMTP \\VRFY\\ command is
+received. See chapter ~~CHAPACL for further details.
+
+.conf admin@_groups "string list" unset
+.index admin user
+If the current group or any of the supplementary groups of the caller is in
+this colon-separated list, the caller has admin privileges. If all your system
+programmers are in a specific group, for example, you can give them all Exim
+admin privileges by putting that group in \admin@_groups\. However, this does
+not permit them to read Exim's spool files (whose group owner is the Exim gid).
+To permit this, you have to add individuals to the Exim group.
+
+.conf allow@_domain@_literals boolean false
+.index domain literal
+If this option is set, the RFC 2822 domain literal format is permitted in
+email addresses. The option is not set by default, because the domain literal
+format is not normally required these days, and few people know about it. It
+has, however, been exploited by mail abusers.
+
+Unfortunately, it seems that some DNS black list maintainers are using this
+format to report black listing to postmasters. If you want to accept messages
+addressed to your hosts by IP address, you need to set
+\allow@_domain@_literals\ true, and also to add \"@@[]"\ to the list of local
+domains (defined in the named domain list \local@_domains\ in the default
+configuration). This `magic string' matches the domain literal form of all the
+local host's IP addresses.
+
+.conf allow@_mx@_to@_ip boolean false
+.index MX record||pointing to IP address
+It appears that more and more DNS zone administrators are breaking the rules
+and putting domain names that look like IP addresses on the right hand side of
+MX records. Exim follows the rules and rejects this, giving an error message
+that explains the mis-configuration. However, some other MTAs support this
+practice, so to avoid `Why can't Exim do this?' complaints, \allow@_mx@_to@_ip\
+exists, in order to enable this heinous activity. It is not recommended, except
+when you have no other choice.
+
+.index domain||UTF-8 characters in
+.index UTF-8||in domain name
+.conf allow@_utf8@_domains boolean false
+Lots of discussion is going on about internationalized domain names. One
+camp is strongly in favour of just using UTF-8 characters, and it seems
+that at least two other MTAs permit this. This option allows Exim users to
+experiment if they wish.
+
+If it is set true, Exim's domain parsing function allows valid
+UTF-8 multicharacters to appear in domain name components, in addition to
+letters, digits, and hyphens. However, just setting this option is not
+enough; if you want to look up these domain names in the DNS, you must also
+adjust the value of \dns@_check@_names@_pattern\ to match the extended form. A
+suitable setting is:
+.display asis
+dns_check_names_pattern = (?i)^(?>(?(1)\.|())[a-z0-9\xc0-\xff]\
+ (?>[-a-z0-9\x80-\xff]*[a-z0-9\x80-\xbf])?)+$
+.endd
+Alternatively, you can just disable this feature by setting
+.display asis
+dns_check_names_pattern =
+.endd
+That is, set the option to an empty string so that no check is done.
+
+.conf auth@_advertise@_hosts "host list$**$" $*$
+.index authentication||advertising
+.index \\AUTH\\||advertising
+If any server authentication mechanisms are configured, Exim advertises them in
+response to an \\EHLO\\ command only if the calling host matches this list.
+Otherwise, Exim does not advertise \\AUTH\\.
+Exim does not accept \\AUTH\\ commands from clients to which it has not
+advertised the availability of \\AUTH\\. The advertising of individual
+authentication mechanisms can be controlled by the use of the
+\server@_advertise@_condition\ generic authenticator option on the individual
+authenticators. See chapter ~~CHAPSMTPAUTH for further details.
+
+Certain mail clients (for example, Netscape) require the user to provide a name
+and password for authentication if \\AUTH\\ is advertised, even though it may
+not be needed (the host may accept messages from hosts on its local LAN without
+authentication, for example). The \auth@_advertise@_hosts\ option can be used
+to make these clients more friendly by excluding them from the set of hosts to
+which Exim advertises \\AUTH\\.
+
+.index \\AUTH\\||advertising when encrypted
+If you want to advertise the availability of \\AUTH\\ only when the connection
+is encrypted using TLS, you can make use of the fact that the value of this
+option is expanded, with a setting like this:
+.display asis
+auth_advertise_hosts = ${if eq{$tls_cipher}{}{}{*}}
+.endd
+If \$tls@_cipher$\ is empty, the session is not encrypted, and the result of
+the expansion is empty, thus matching no hosts. Otherwise, the result of the
+expansion is $*$, which matches all hosts.
+
+.conf auto@_thaw time 0s
+.index thawing messages
+.index unfreezing messages
+If this option is set to a time greater than zero, a queue runner will try a
+new delivery attempt on any frozen message if this much time has passed since
+it was frozen. This may result in the message being re-frozen if nothing has
+changed since the last attempt. It is a way of saying `keep on trying, even
+though there are big problems'. See also \timeout@_frozen@_after\ and
+\ignore@_bounce@_errors@_after\.
+
+.conf bi@_command string unset
+.index \-bi-\ option
+This option supplies the name of a command that is run when Exim is called with
+the \-bi-\ option (see chapter ~~CHAPcommandline). The string value is just the
+command name, it is not a complete command line. If an argument is required, it
+must come from the \-oA-\ command line option.
+
+.conf bounce@_message@_file string unset
+.index bounce message||customizing
+.index customizing||bounce message
+This option defines a template file containing paragraphs of text to be used
+for constructing bounce messages. Details of the file's contents are given in
+chapter ~~CHAPemsgcust. See also \warn@_message@_file\.
+
+.conf bounce@_message@_text string unset
+When this option is set, its contents are included in the default bounce
+message immediately after `This message was created automatically by mail
+delivery software.' It is not used if \bounce@_message@_file\ is set.
+
+.index bounce message||including body
+.conf bounce@_return@_body boolean true
+This option controls whether the body of an incoming message is included in a
+bounce message when \bounce@_return@_message\ is true. If it is not set, only
+the message header is included.
+
+.index bounce message||including original
+.conf bounce@_return@_message boolean true
+If this option is set false, the original message is not included in bounce
+messages generated by Exim. See also \bounce@_return@_size@_limit\.
+
+.conf bounce@_return@_size@_limit integer 100K
+.index size||of bounce, limit
+.index bounce message||size limit
+.index limit||bounce message size
+This option sets a limit in bytes on the size of messages that are returned to
+senders as part of bounce messages when \bounce@_return@_message\ is true. The
+limit should be less than the value of the global \message@_size@_limit\ and of
+any \message@_size@_limit\ settings on transports, to allow for the bounce text
+that Exim generates. If this option is set to zero there is no limit.
+
+When the body of any message that is to be included in a bounce message is
+greater than the limit, it is truncated, and a comment pointing this out is
+added at the top. The actual cutoff may be greater than the value given, owing
+to the use of buffering for transferring the message in chunks (typically 8K in
+size). The idea is to save bandwidth on those undeliverable 15-megabyte
+messages.
+
+.index bounce message||sender authentication
+.index authentication||bounce message
+.index \\AUTH\\||on bounce message
+.conf bounce@_sender@_authentication string unset
+This option provides an authenticated sender address that is sent with any
+bounce messages generated by Exim that are sent over an authenticated SMTP
+connection. A typical setting might be:
+.display asis
+bounce_sender_authentication = mailer-daemon@my.domain.example
+.endd
+which would cause bounce messages to be sent using the SMTP command:
+.display asis
+MAIL FROM:<> AUTH=mailer-daemon@my.domain.example
+.endd
+The value of \bounce@_sender@_authentication\ must always be a complete email
+address.
+
+.index caching||callout, timeouts
+.index callout||caching timeouts
+.conf callout@_domain@_negative@_expire time 3h
+This option specifies the expiry time for negative callout cache data for a
+domain. See section ~~SECTcallver for details of callout verification, and
+section ~~SECTcallvercache for details of the caching.
+
+.conf callout@_domain@_positive@_expire time 7d
+This option specifies the expiry time for positive callout cache data for a
+domain. See section ~~SECTcallver for details of callout verification, and
+section ~~SECTcallvercache for details of the caching.
+
+.conf callout@_negative@_expire time 2h
+This option specifies the expiry time for negative callout cache data for an
+address. See section ~~SECTcallver for details of callout verification, and
+section ~~SECTcallvercache for details of the caching.
+
+.conf callout@_positive@_expire time 24h
+This option specifies the expiry time for positive callout cache data for an
+address. See section ~~SECTcallver for details of callout verification, and
+section ~~SECTcallvercache for details of the caching.
+
+.conf callout@_random@_local@_part string$**$ "see below"
+This option defines the `random' local part that can be used as part of callout
+verification. The default value is
+.display asis
+$primary_host_name-$tod_epoch-testing
+.endd
+See section ~~CALLaddparcall for details of how this value is used.
+
+.conf check@_log@_inodes integer 0
+See \check@_spool@_space\ below.
+
+.conf check@_log@_space integer 0
+See \check@_spool@_space\ below.
+
+.conf check@_spool@_inodes integer 0
+See \check@_spool@_space\ below.
+
+.conf check@_spool@_space integer 0
+.index checking disk space
+.index disk space, checking
+.index spool directory||checking space
+The four \check@_...\ options allow for checking of disk resources before a
+message is accepted. \check@_spool@_space\ and \check@_spool@_inodes\ check the
+spool partition if either value is greater than zero, for example:
+.display asis
+check_spool_space = 10M
+check_spool_inodes = 100
+.endd
+The spool partition is the one which contains the directory defined by
+\\SPOOL@_DIRECTORY\\ in \(Local/Makefile)\. It is used for holding messages in
+transit.
+
+\check@_log@_space\ and \check@_log@_inodes\ check the partition in which log
+files are written if either is greater than zero. These should be set only if
+\log@_file@_path\ and \spool@_directory\ refer to different partitions.
+
+If there is less space or fewer inodes than requested, Exim refuses to accept
+incoming mail. In the case of SMTP input this is done by giving a 452 temporary
+error response to the \\MAIL\\ command. If ESMTP is in use and there was a
+\\SIZE\\ parameter on the \\MAIL\\ command, its value is added to the
+\check@_spool@_space\ value, and the check is performed even if
+\check@_spool@_space\ is zero, unless \no@_smtp@_check@_spool@_space\ is set.
+
+The values for \check@_spool@_space\ and \check@_log@_space\ are held as a
+number of kilobytes. If a non-multiple of 1024 is specified, it is rounded up.
+
+For non-SMTP input and for batched SMTP input, the test is done at start-up; on
+failure a message is written to stderr and Exim exits with a non-zero code, as
+it obviously cannot send an error message of any kind.
+
+.index port||for daemon
+.index TCP/IP||setting listening ports
+.conf daemon@_smtp@_ports string "$tt{smtp}"
+This option specifies one or more default SMTP ports on which the Exim daemon
+listens. See chapter ~~CHAPinterfaces for details of how it is used. For
+backward compatibility, \daemon@_smtp@_port\ (singular) is a synonym.
+
+.conf delay@_warning "time list" 24h
+.index warning of delay
+.index delay warning, specifying
+When a message is delayed, Exim sends a warning message to the sender at
+intervals specified by this option. If it is set to a zero, no warnings are
+sent. The data is a colon-separated list of times after which to send warning
+messages. Up to 10 times may be given. If a message has been on the queue for
+longer than the last time, the last interval between the times is used to
+compute subsequent warning times. For example, with
+.display asis
+delay_warning = 4h:8h:24h
+.endd
+the first message is sent after 4 hours, the second after 8 hours, and
+the third one after 24 hours. After that, messages are sent every 16 hours,
+because that is the interval between the last two times on the list. If you set
+just one time, it specifies the repeat interval. For example, with:
+.display asis
+delay_warning = 6h
+.endd
+messages are repeated every six hours. To stop warnings after a given time, set
+a very large time at the end of the list. For example:
+.display asis
+delay_warning = 2h:12h:99d
+.endd
+
+.conf delay@_warning@_condition string$**$ "see below"
+The string is expanded at the time a warning message might be sent. If all the
+deferred addresses have the same domain, it is set in \$domain$\ during the
+expansion. Otherwise \$domain$\ is empty. If the result of the expansion is a
+forced failure, an empty string, or a string matching any of `0', `no' or
+`false' (the comparison being done caselessly) then the warning message is not
+sent. The default is
+.display asis
+delay_warning_condition = \
+ ${if match{$h_precedence:}{(?i)bulk|list|junk}{no}{yes}}
+.endd
+which suppresses the sending of warnings about messages that have `bulk',
+`list' or `junk' in a ::Precedence:: header.
+
+.index unprivileged delivery
+.index delivery||unprivileged
+.conf deliver@_drop@_privilege boolean false
+If this option is set true, Exim drops its root privilege at the start of a
+delivery process, and runs as the Exim user throughout. This severely restricts
+the kinds of local delivery that are possible, but is viable in certain types
+of configuration. There is a discussion about the use of root privilege in
+chapter ~~CHAPsecurity.
+
+.index load average
+.index queue runner||abandoning
+.conf deliver@_queue@_load@_max fixed-point unset
+When this option is set, a queue run is abandoned if the system load average
+becomes greater than the value of the option. The option has no effect on
+ancient operating systems on which Exim cannot determine the load average.
+See also \queue@_only@_load\ and \smtp@_load@_reserve\.
+
+.conf delivery@_date@_remove boolean true
+.index ::Delivery-date:: header line
+Exim's transports have an option for adding a ::Delivery-date:: header to a
+message when it is delivered -- in exactly the same way as ::Return-path:: is
+handled. ::Delivery-date:: records the actual time of delivery. Such headers
+should not be present in incoming messages, and this option causes them to be
+removed at the time the message is received, to avoid any problems that might
+occur when a delivered message is subsequently sent on to some other recipient.
+
+.index DNS||`try again' response, overriding
+.conf dns@_again@_means@_nonexist "domain list$**$" unset
+DNS lookups give a `try again' response for the DNS errors `non-authoritative
+host not found' and `\\SERVERFAIL\\'. This can cause Exim to keep trying to
+deliver a message, or to give repeated temporary errors to incoming mail.
+Sometimes the effect is caused by a badly set up name server and may persist
+for a long time. If a domain which exhibits this problem matches anything in
+\dns__again__means__nonexist\, it is treated as if it did not exist. This
+option should be used with care.
+.em
+You can make it apply to reverse lookups by a setting such as this:
+.display asis
+dns_again_means_nonexist = *.in-addr.arpa
+.endd
+.nem
+
+.index DNS||pre-check of name syntax
+.conf dns@_check@_names@_pattern string "see below"
+When this option is set to a non-empty string, it causes Exim to check domain
+names for illegal characters before handing them to the DNS resolver, because
+some resolvers give temporary errors for malformed names. If a domain name
+contains any illegal characters, a `not found' result is forced, and the
+resolver is not called. The check is done by matching the domain name against a
+regular expression, which is the value of this option. The default pattern is
+.display asis
+dns_check_names_pattern = \
+ (?i)^(?>(?(1)\.|())[^\W_](?>[a-z0-9-]*[^\W_])?)+$
+.endd
+which permits only letters, digits, and hyphens in components, but they may not
+start or end with a hyphen.
+If you set \allow@_utf8@_domains\, you must modify this pattern, or set the
+option to an empty string.
+
+.conf dns@_ipv4@_lookup "domain list$**$" unset
+.index IPv6||DNS lookup for AAAA records
+.index DNS||IPv6 lookup for AAAA records
+When Exim is compiled with IPv6 support, it looks for IPv6 address records
+(AAAA and, if configured, A6) as well as IPv4 address records when trying to
+find IP addresses for hosts, unless the host's domain matches this list.
+
+This is a fudge to help with name servers that give big delays or otherwise do
+not work for the new IPv6 record types. If Exim is handed an IPv6 address
+record as a result of an MX lookup, it always recognizes it, and may as a
+result make an outgoing IPv6 connection. All this option does is to make Exim
+look only for IPv4-style A records when it needs to find an IP address for a
+host name. In due course, when the world's name servers have all been upgraded,
+there should be no need for this option.
+
+.conf dns@_retrans time 0s
+.index DNS||resolver options
+The options \dns@_retrans\ and \dns@_retry\ can be used to set the
+retransmission and retry parameters for DNS lookups. Values of zero (the
+defaults) leave the system default settings unchanged. The first value is the
+time between retries, and the second is the number of retries. It isn't
+totally clear exactly how these settings affect the total time a DNS lookup may
+take. I haven't found any documentation about timeouts on DNS lookups; these
+parameter values are available in the external resolver interface structure,
+but nowhere does it seem to describe how they are used or what you might want
+to set in them.
+
+.conf dns@_retry integer 0
+See \dns@_retrans\ above.
+
+.conf drop@_cr boolean false
+This is an obsolete option that is now a no-op. It used to affect the way Exim
+handled CR and LF characters in incoming messages. What happens now is
+described in section ~~SECTlineendings.
+
+.conf envelope@_to@_remove boolean true
+.index ::Envelope-to:: header line
+Exim's transports have an option for adding an ::Envelope-to:: header to a
+message when it is delivered -- in exactly the same way as ::Return-path:: is
+handled. ::Envelope-to:: records the original recipient address from the
+messages's envelope that caused the delivery to happen. Such headers should not
+be present in incoming messages, and this option causes them to be removed at
+the time the message is received, to avoid any problems that might occur when a
+delivered message is subsequently sent on to some other recipient.
+
+.conf errors@_copy "string list$**$" unset
+.index bounce message||copy to other address
+.index copy of bounce message
+Setting this option causes Exim to send bcc copies of bounce messages that it
+generates to other addresses. \**Note**\: this does not apply to bounce messages
+coming from elsewhere. The value of the option is a colon-separated list of
+items. Each item consists of a pattern, terminated by white space, followed by
+a comma-separated list of email addresses. If a pattern contains spaces, it
+must be enclosed in double quotes.
+
+Each pattern is processed in the same way as a single item in an address list
+(see section ~~SECTaddresslist). When a pattern matches the recipient of the
+bounce message, the message is copied to the addresses on the list. The items
+are scanned in order, and once a matching one is found, no further items are
+examined. For example:
+.display asis
+errors_copy = spqr@mydomain postmaster@mydomain.example :\
+ rqps@mydomain hostmaster@mydomain.example,\
+ postmaster@mydomain.example
+.endd
+The address list is expanded before use. The expansion variables
+\$local@_part$\ and \$domain$\ are set from the original recipient of the error
+message, and if there was any wildcard matching in the pattern, the expansion
+.index numerical variables (\$1$\, \$2$\, etc)||in \errors@_copy\
+variables \$0$\, \$1$\, etc. are set in the normal way.
+
+.conf errors@_reply@_to string unset
+.index bounce message||::Reply-to:: in
+Exim's bounce and delivery warning messages contain the header line
+.display
+From: Mail Delivery System @<Mailer-Daemon@@<<qualify-domain>>@>
+.endd
+where <<qualify-domain>> is the value of the \qualify@_domain\ option.
+Experience shows that people reply to bounce messages. If the
+\errors@_reply@_to\ option is set, a ::Reply-To:: header is added to bounce and
+warning messages. For example:
+.display asis
+errors_reply_to = postmaster@my.domain.example
+.endd
+The value of the option is not expanded. It must specify a valid RFC 2822
+address.
+
+.conf exim@_group string "compile-time configured"
+.index gid (group id)||Exim's own
+.index Exim group
+This option changes the gid under which Exim runs when it gives up root
+privilege. The default value is compiled into the binary. The value of this
+option is used only when \exim@_user\ is also set. Unless it consists entirely
+of digits, the string is looked up using \*getgrnam()*\, and failure causes a
+configuration error. See chapter ~~CHAPsecurity for a discussion of security
+issues.
+
+.conf exim@_path string "see below"
+.index Exim binary, path name
+This option specifies the path name of the Exim binary, which is used when Exim
+needs to re-exec itself. The default is set up to point to the file \*exim*\ in
+the directory configured at compile time by the \\BIN@_DIRECTORY\\ setting. It
+is necessary to change \exim@_path\ if, exceptionally, Exim is run from some
+other place.
+\**Warning**\: Do not use a macro to define the value of this option, because
+you will break those Exim utilities that scan the configuration file to find
+where the binary is. (They then use the \-bP-\ option to extract option
+settings such as the value of \spool@_directory\.)
+
+.conf exim@_user string "compile-time configured"
+.index uid (user id)||Exim's own
+.index Exim user
+This option changes the uid under which Exim runs when it gives up root
+privilege. The default value is compiled into the binary. Ownership of the run
+time configuration file and the use of the \-C-\ and \-D-\ command line options
+is checked against the values in the binary, not what is set here.
+
+Unless it consists entirely of digits, the string is looked up using
+\*getpwnam()*\, and failure causes a configuration error. If \exim@_group\ is
+not also supplied, the gid is taken from the result of \*getpwnam()*\ if it is
+used. See chapter ~~CHAPsecurity for a discussion of security issues.
+
+.conf extra@_local@_interfaces "string list" unset
+.index
+This option defines network interfaces that are to be considered local when
+routing, but which are not used for listening by the daemon. See section
+~~SECTreclocipadd for details.
+
+.conf extract@_addresses@_remove@_arguments boolean true
+.index \-t-\ option
+.index command line||addresses with \-t-\
+.index Sendmail compatibility||\-t-\ option
+According to some Sendmail documentation (Sun, IRIX, HP-UX), if any addresses
+are present on the command line when the \-t-\ option is used to build an
+envelope from a message's ::To::, ::Cc:: and ::Bcc:: headers, the command line
+addresses are removed from the recipients list. This is also how Smail behaves.
+However, other Sendmail documentation (the O'Reilly book) states that command
+line addresses are added to those obtained from the header lines. When
+\extract@_addresses@_remove@_arguments\ is true (the default), Exim subtracts
+argument headers. If it is set false, Exim adds rather than removes argument
+addresses.
+
+.conf finduser@_retries integer 0
+.index NIS, looking up users, retrying
+On systems running NIS or other schemes in which user and group information is
+distributed from a remote system, there can be times when \*getpwnam()*\ and
+related functions fail, even when given valid data, because things time out.
+Unfortunately these failures cannot be distinguished from genuine `not found'
+errors. If \finduser@_retries\ is set greater than zero, Exim will try that
+many extra times to find a user or a group, waiting for one second between
+retries.
+
+.conf freeze@_tell "string list, comma separated" unset
+.index freezing messages||sending a message when freezing
+On encountering certain errors, or when configured to do so in a system filter,
+or in an ACL,
+Exim freezes a message. This means that no further delivery attempts take place
+until an administrator (or the \auto@_thaw\ feature) thaws the message. If
+\freeze@_tell\ is set, Exim generates a warning message whenever it freezes
+something, unless the message it is freezing is a
+locally-generated
+bounce message. (Without this exception there is the possibility of looping.)
+The warning message is sent to the addresses supplied as the comma-separated
+value of this option. If several of the message's addresses cause freezing,
+only a single message is sent.
+If the freezing was automatic, the reason(s) for freezing can be found in the
+message log. If you configure freezing in a filter or ACL, you must arrange for
+any logging that you require.
+
+.conf gecos@_name string$**$ unset
+.index HP-UX
+.index `gecos' field, parsing
+Some operating systems, notably HP-UX, use the `gecos' field in the system
+password file to hold other information in addition to users' real names. Exim
+looks up this field for use when it is creating ::Sender:: or ::From:: headers.
+If either \gecos@_pattern\ or \gecos@_name\ are unset, the contents of the
+field are used unchanged, except that, if an ampersand is encountered, it is
+replaced by the user's login name with the first character forced to
+upper case, since this is a convention that is observed on many systems.
+
+When these options are set, \gecos@_pattern\ is treated as a regular expression
+that is to be applied to the field (again with & replaced by the login name),
+and if it matches, \gecos@_name\ is expanded and used as the user's name.
+.index numerical variables (\$1$\, \$2$\, etc)||in \gecos@_name\
+Numeric variables such as \$1$\, \$2$\, etc. can be used in the expansion to
+pick up sub-fields that were matched by the pattern. In HP-UX, where the user's
+name terminates at the first comma, the following can be used:
+.display asis
+gecos_pattern = ([^,]*)
+gecos_name = $1
+.endd
+
+.conf gecos@_pattern string unset
+See \gecos@_name\ above.
+
+.conf headers@_charset string "see below"
+This option sets a default character set for translating from encoded MIME
+`words' in header lines, when referenced by an \$h@_xxx$\ expansion item. The
+default is the value of \\HEADERS@_CHARSET\\ in \(Local/Makefile)\. The
+ultimate default is ISO-8859-1. For more details see the description of header
+insertions in section ~~SECTexpansionitems.
+
+
+.conf header@_maxsize integer "see below"
+.index header section||maximum size of
+.index limit||size of message header section
+This option controls the overall maximum size of a message's header
+section. The default is the value of \\HEADER@_MAXSIZE\\ in
+\(Local/Makefile)\; the default for that is 1M. Messages with larger header
+sections are rejected.
+
+.conf header@_line@_maxsize integer 0
+.index header lines||maximum size of
+.index limit||size of one header line
+This option limits the length of any individual header line in a message, after
+all the continuations have been joined together. Messages with individual
+header lines that are longer than the limit are rejected. The default value of
+zero means `no limit'.
+
+
+
+.conf helo@_accept@_junk@_hosts "host list$**$" unset
+.index \\HELO\\||accepting junk data
+.index \\EHLO\\||accepting junk data
+Exim checks the syntax of \\HELO\\ and \\EHLO\\ commands for incoming SMTP
+mail, and gives an error response for invalid data. Unfortunately, there are
+some SMTP clients that send syntactic junk. They can be accommodated by setting
+this option. Note that this is a syntax check only. See \helo@_verify@_hosts\
+if you want to do semantic checking.
+See also \helo@_allow@_chars\ for a way of extending the permitted character
+set.
+
+.conf helo@_allow@_chars string unset
+.index \\HELO\\||underscores in
+.index \\EHLO\\||underscores in
+.index underscore in \\EHLO\\/\\HELO\\
+This option can be set to a string of rogue characters that are permitted in
+all \\EHLO\\ and \\HELO\\ names in addition to the standard letters, digits,
+hyphens, and dots. If you really must allow underscores, you can set
+.display asis
+helo_allow_chars = _
+.endd
+Note that the value is one string, not a list.
+
+.conf helo@_lookup@_domains "domain list$**$" "$tt{@@:@@[]}"
+.index \\HELO\\||forcing reverse lookup
+.index \\EHLO\\||forcing reverse lookup
+If the domain given by a client in a \\HELO\\ or \\EHLO\\ command matches this
+list, a reverse lookup is done in order to establish the host's true name. The
+default forces a lookup if the client host gives the server's name or any of
+its IP addresses (in brackets), something that broken clients have been seen to
+do.
+
+.conf helo@_try@_verify@_hosts "host list$**$" unset
+.index \\HELO\\||verifying, optional
+.index \\EHLO\\||verifying, optional
+The RFCs mandate that a server must not reject a message because it doesn't
+like the \\HELO\\ or \\EHLO\\ command. By default, Exim just checks the syntax
+of these commands (see \helo__accept__junk__hosts\ and \helo@_allow@_chars\
+above). However, some sites like to be stricter. If the calling host matches
+\helo@_try@_verify@_hosts\, Exim checks that the host name given in the \\HELO\\
+or \\EHLO\\ command either:
+.numberpars $.
+is an IP literal matching the calling address of the host (the RFCs
+specifically allow this), or
+.nextp
+.index DNS||reverse lookup
+.index reverse DNS lookup
+matches the host name that Exim obtains by doing a reverse lookup of the
+calling host address, or
+.nextp
+when looked up using \*gethostbyname()*\ (or \*getipnodebyname()*\ when
+available) yields the calling host address.
+.endp
+However, the \\EHLO\\ or \\HELO\\ command is not rejected if any of the checks
+fail. Processing continues, but the result of the check is remembered, and can
+be detected later in an ACL by the \"verify = helo"\ condition. If you want
+verification failure to cause rejection of \\EHLO\\ or \\HELO\\, use
+\helo@_verify@_hosts\ instead.
+
+
+.conf helo@_verify@_hosts "host list$**$" unset
+.index \\HELO\\||verifying, mandatory
+.index \\EHLO\\||verifying, mandatory
+For hosts that match this option, Exim checks the host name given in the
+\\HELO\\ or \\EHLO\\ in the same way as for \helo@_try@_verify@_hosts\. If the
+check fails, the \\HELO\\ or \\EHLO\\ command is rejected with a 550 error, and
+entries are written to the main and reject logs. If a \\MAIL\\ command is
+received before \\EHLO\\ or \\HELO\\, it is rejected with a
+503
+error.
+
+.conf hold@_domains "domain list$**$" unset
+.index domain||delaying delivery
+.index delivery||delaying certain domains
+This option allows mail for particular domains to be held on the queue
+manually. The option is overridden if a message delivery is forced with the
+\-M-\, \-qf-\, \-Rf-\ or \-Sf-\ options, and also while testing or verifying
+addresses using \-bt-\ or \-bv-\. Otherwise, if a domain matches an item in
+\hold@_domains\, no routing or delivery for that address is done, and it is
+deferred every time the message is looked at.
+
+This option is intended as a temporary operational measure for delaying the
+delivery of mail while some problem is being sorted out, or some new
+configuration tested. If you just want to delay the processing of some
+domains until a queue run occurs, you should use \queue@_domains\ or
+\queue@_smtp@_domains\, not \hold@_domains\.
+
+A setting of \hold@_domains\ does not override Exim's code for removing
+messages from the queue if they have been there longer than the longest retry
+time in any retry rule. If you want to hold messages for longer than the normal
+retry times, insert a dummy retry rule with a long retry time.
+
+.conf host@_lookup "host list$**$" unset
+.index host||name lookup, forcing
+Exim does not look up the name of a calling host from its IP address unless it
+is required to compare against some host list, or the host matches
+\helo@_try@_verify@_hosts\ or \helo@_verify@_hosts\, or the host matches this
+option (which normally contains IP addresses rather than host names). The
+default configuration file contains
+.display asis
+host_lookup = *
+.endd
+which causes a lookup to happen for all hosts. If the expense of these lookups
+is felt to be too great, the setting can be changed or removed.
+
+After a successful reverse lookup, Exim does a forward lookup on the name it
+has obtained, to verify that it yields the IP address that it started with. If
+this check fails, Exim behaves as if the name lookup failed.
+
+After any kind of failure, the host name (in \$sender@_host@_name$\) remains
+unset, and \$host@_lookup@_failed$\ is set to the string `1'. See also
+\dns@_again@_means@_nonexist\, \helo__lookup__domains\, and \"verify =
+reverse@_host@_lookup"\ in ACLs.
+
+.conf host@_lookup@_order "string list" $tt{bydns:byaddr}
+This option specifies the order of different lookup methods when Exim is trying
+to find a host name from an IP address. The default is to do a DNS lookup
+first, and then to try a local lookup (using \*gethostbyaddr()*\ or equivalent)
+if that fails. You can change the order of these lookups, or omit one entirely,
+if you want.
+
+\**Warning**\: the `byaddr' method does not always yield aliases when there are
+multiple PTR records in the DNS and the IP address is not listed in
+\(/etc/hosts)\. Different operating systems give different results in this
+case. That is why the default tries a DNS lookup first.
+
+
+.conf host@_reject@_connection "host list$**$" unset
+.index host||rejecting connections from
+If this option is set, incoming SMTP calls from the hosts listed are rejected
+as soon as the connection is made.
+This option is obsolete, and retained only for backward compatibility, because
+nowadays the ACL specified by \acl@_smtp@_connect\ can also reject incoming
+connections immediately.
+
+The ability to give an immediate rejection (either by this option or using an
+ACL) is provided for use in unusual cases. Many hosts will just try again,
+sometimes without much delay. Normally, it is better to use an ACL to reject
+incoming messages at a later stage, such as after \\RCPT\\ commands. See
+chapter ~~CHAPACL.
+
+.conf hosts@_treat@_as@_local "domain list$**$" unset
+.index local host||domains treated as
+.index host||treated as local
+If this option is set, any host names that match the domain list are treated as
+if they were the local host when Exim is scanning host lists obtained from MX
+records
+or other sources. Note that the value of this option is a domain list, not a
+host list, because it is always used to check host names, not IP addresses.
+
+This option also applies when Exim is matching the special items
+\"@@mx@_any"\, \"@@mx@_primary"\, and \"@@mx@_secondary"\ in a domain list (see
+section ~~SECTdomainlist), and when checking the \hosts\ option in the \%smtp%\
+transport for the local host (see the \allow@_localhost\ option in that
+transport).
+See also \local@_interfaces\, \extra@_local@_interfaces\, and chapter
+~~CHAPinterfaces, which contains a discussion about local network interfaces
+and recognising the local host.
+
+.conf ignore@_bounce@_errors@_after time 10w
+.index bounce message||discarding
+.index discarding bounce message
+This option affects the processing of bounce messages that cannot be delivered,
+that is, those that suffer a permanent delivery failure. (Bounce messages that
+suffer temporary delivery failures are of course retried in the usual way.)
+
+After a permanent delivery failure, bounce messages are frozen,
+because there is no sender to whom they can be returned. When a frozen bounce
+message has been on the queue for more than the given time, it is unfrozen at
+the next queue run, and a further delivery is attempted. If delivery fails
+again, the bounce message is discarded. This makes it possible to keep failed
+bounce messages around for a shorter time than the normal maximum retry time
+for frozen messages. For example,
+.display asis
+ignore_bounce_errors_after = 12h
+.endd
+retries failed bounce message deliveries after 12 hours, discarding any further
+failures. If the value of this option is set to a zero time period, bounce
+failures are discarded immediately. Setting a very long time (as in the default
+value) has the effect of disabling this option. For ways of automatically
+dealing with other kinds of frozen message, see \auto@_thaw\ and
+\timeout@_frozen@_after\.
+
+.conf ignore@_fromline@_hosts "host list$**$" unset
+.index `From' line
+.index UUCP||`From' line
+Some broken SMTP clients insist on sending a UUCP-like `From' line before the
+headers of a message. By default this is treated as the start of the message's
+body, which means that any following headers are not recognized as such. Exim
+can be made to ignore it by setting \ignore@_fromline@_hosts\ to match those
+hosts that insist on sending it. If the sender is actually a local process
+rather than a remote host, and is using \-bs-\ to inject the messages,
+\ignore__fromline__local\ must be set to achieve this effect.
+
+.conf ignore@_fromline@_local boolean false
+See \ignore@_fromline@_hosts\ above.
+
+.conf keep@_malformed time 4d
+This option specifies the length of time to keep messages whose spool files
+have been corrupted in some way. This should, of course, never happen. At the
+next attempt to deliver such a message, it gets removed. The incident is
+logged.
+
+.conf ldap@_default@_servers "string list" unset
+.index LDAP||default servers
+This option provides a list of LDAP servers which are tried in turn when an
+LDAP query does not contain a server. See section ~~SECTforldaque for details
+of LDAP queries. This option is available only when Exim has been built with
+LDAP support.
+
+.conf ldap@_version integer unset
+.index LDAP||protocol version, forcing
+This option can be used to force Exim to set a specific protocol version for
+LDAP. If it option is unset, it is shown by the \-bP-\ command line option as
+-1. When this is the case, the default is 3 if \\LDAP@_VERSION3\\ is defined in
+the LDAP headers; otherwise it is 2. This option is available only when Exim
+has been built with LDAP support.
+
+
+.conf local@_from@_check boolean true
+.index ::Sender:: header line||disabling addition of
+.index ::From:: header line||disabling checking of
+When a message is submitted locally (that is, not over a TCP/IP connection) by
+an untrusted user, Exim removes any existing ::Sender:: header line, and checks
+that the ::From:: header line matches the login of the calling user. You can
+use \local@_from@_prefix\ and \local@_from@_suffix\ to permit affixes on the
+local part. If the ::From:: header line does not match, Exim adds a ::Sender::
+header with an address constructed from the calling user's login and the
+default qualify domain.
+
+If \local@_from@_check\ is set false, the ::From:: header check is disabled,
+and no ::Sender:: header is ever added. If, in addition, you want to retain
+::Sender:: header lines supplied by untrusted users, you must also set
+\local@_sender@_retain\ to be true.
+
+.index envelope sender
+These options affect only the header lines in the message. The envelope sender
+is still forced to be the login id at the qualify domain unless
+\untrusted@_set@_sender\ permits the user to supply an envelope sender.
+Section ~~SECTthesenhea has more details about ::Sender:: processing.
+
+
+.conf local@_from@_prefix string unset
+When Exim checks the ::From:: header line of locally submitted messages for
+matching the login id (see \local@_from@_check\ above), it can be configured to
+ignore certain prefixes and suffixes in the local part of the address. This is
+done by setting \local@_from@_prefix\ and/or \local@_from@_suffix\ to
+appropriate lists, in the same form as the \local@_part@_prefix\ and
+\local@_part@_suffix\ router options (see chapter ~~CHAProutergeneric). For
+example, if
+.display asis
+local_from_prefix = *-
+.endd
+is set, a ::From:: line containing
+.display asis
+From: anything-user@your.domain.example
+.endd
+will not cause a ::Sender:: header to be added if \*user@@your.domain.example*\
+matches the actual sender address that is constructed from the login name and
+qualify domain.
+
+.conf local@_from@_suffix string unset
+See \local@_from@_prefix\ above.
+
+.conf local@_interfaces "string list" "see below"
+This option controls which network interfaces are used by the daemon for
+listening; they are also used to identify the local host when routing. Chapter
+~~CHAPinterfaces contains a full description of this option and the related
+options \extra@_local@_interfaces\ and \hosts@_treat@_as@_local\. The default
+value for \local@_interfaces\ is
+.display asis
+local_interfaces = 0.0.0.0
+.endd
+when Exim is built without IPv6 support; otherwise it is
+.display asis
+local_interfaces = <; ::0 ; 0.0.0.0
+.endd
+
+.conf local@_scan@_timeout time 5m
+.index timeout||for \*local@_scan()*\ function
+.index \*local@_scan()*\ function||timeout
+This timeout applies to the \*local@_scan()*\ function (see chapter
+~~CHAPlocalscan). Zero means `no timeout'. If the timeout is exceeded, the
+incoming message is rejected with a temporary error if it is an SMTP message.
+For a non-SMTP message, the message is dropped and Exim ends with a non-zero
+code. The incident is logged on the main and reject logs.
+
+
+.conf local@_sender@_retain boolean false
+.index ::Sender:: header line||retaining from local submission
+When a message is submitted locally (that is, not over a TCP/IP connection) by
+an untrusted user, Exim removes any existing ::Sender:: header line. If you
+do not want this to happen, you must set \local@_sender@_retain\, and you must
+also set \local@_from@_check\ to be false (Exim will complain if you do not).
+Section ~~SECTthesenhea has more details about ::Sender:: processing.
+
+
+
+.conf localhost@_number string$**$ unset
+.index host||locally unique number for
+.index message||ids, with multiple hosts
+Exim's message ids are normally unique only within the local host. If
+uniqueness among a set of hosts is required, each host must set a different
+value for the \localhost@_number\ option. The string is expanded immediately
+after reading the configuration file (so that a number can be computed from the
+host name, for example) and the result of the expansion must be a number in the
+range 0--16 (or 0--10 on operating systems with case-insensitive file systems).
+This is available in subsequent string expansions via the variable
+\$localhost@_number$\. When \localhost@_number is set\, the final two
+characters of the message id, instead of just being a fractional part of the
+time, are computed from the time and the local host number as described in
+section ~~SECTmessiden.
+
+
+.conf log@_file@_path "string list$**$" "set at compile time"
+.index log||file path for
+This option sets the path which is used to determine the names of Exim's log
+files, or indicates that logging is to be to syslog, or both. It is expanded
+when Exim is entered, so it can, for example, contain a reference to the host
+name. If no specific path is set for the log files at compile or run time, they
+are written in a sub-directory called \(log)\ in Exim's spool directory.
+Chapter ~~CHAPlog contains further details about Exim's logging, and section
+~~SECTwhelogwri describes how the contents of \log@_file@_path\ are used. If
+this string is fixed at your installation (contains no expansion variables) it
+is recommended that you do not set this option in the configuration file, but
+instead supply the path using \\LOG@_FILE@_PATH\\ in \(Local/Makefile)\ so that
+it is available to Exim for logging errors detected early on -- in particular,
+failure to read the configuration file.
+
+.conf log@_selector string unset
+.index log||selectors
+This option can be used to reduce or increase the number of things that Exim
+writes to its log files. Its argument is made up of names preceded by plus or
+minus characters. For example:
+.display asis
+log_selector = +arguments -retry_defer
+.endd
+A list of possible names and what they control is given in the chapter on
+logging, in section ~~SECTlogselector.
+
+.conf log@_timezone boolean false
+.index log||timezone for entries
+By default, the timestamps on log lines are in local time without the
+timezone. This means that if your timezone changes twice a year, the timestamps
+in log lines are ambiguous for an hour when the clocks go back. One way of
+avoiding this problem is to set the timezone to UTC. An alternative is to set
+\log@_timezone\ true. This turns on the addition of the timezone offset to
+timestamps in log lines. Turning on this option can add quite a lot to the size
+of log files because each line is extended by 6 characters. Note that the
+\$tod@_log$\ variable contains the log timestamp without the zone, but there is
+another variable called \$tod@_zone$\ that contains just the timezone offset.
+
+.conf lookup@_open@_max integer 25
+.index too many open files
+.index open files, too many
+.index file||too many open
+.index lookup||maximum open files
+.index limit||open files for lookups
+This option limits the number of simultaneously open files for single-key
+lookups that use regular files (that is, \%lsearch%\, \%dbm%\, and \%cdb%\). Exim
+normally keeps these files open during routing, because often the same file is
+required several times. If the limit is reached, Exim closes the least recently
+used file. Note that if you are using the \*ndbm*\ library, it actually opens
+two files for each logical DBM database, though it still counts as one for the
+purposes of \lookup@_open@_max\. If you are getting `too many open files'
+errors with NDBM, you need to reduce the value of \lookup@_open@_max\.
+
+.conf max@_username@_length integer 0
+.index length of login name
+.index user name||maximum length
+.index limit||user name length
+Some operating systems are broken in that they truncate long arguments to
+\*getpwnam()*\ to eight characters, instead of returning `no such user'. If
+this option is set greater than zero, any attempt to call \*getpwnam()*\ with
+an argument that is longer behaves as if \*getpwnam()*\ failed.
+
+
+.conf message@_body@_visible integer 500
+.index body of message||visible size
+.index message||body, visible size
+This option specifies how much of a message's body is to be included in the
+\$message@_body$\ and \$message@_body@_end$\ expansion variables.
+
+.conf message@_id@_header@_domain string$**$ unset
+.index ::Message-ID:: header line
+If this option is set, the string is expanded and used as the right hand side
+(domain) of the ::Message-ID:: header that Exim creates if a
+locally-originated incoming message does not have one. `Locally-originated'
+means `not received over TCP/IP.'
+Otherwise, the primary host name is used.
+Only letters, digits, dot and hyphen are accepted; any other characters are
+replaced by hyphens. If the expansion is forced to fail, or if the result is an
+empty string, the option is ignored.
+
+.conf message@_id@_header@_text string$**$ unset
+If this variable is set, the string is expanded and used to augment the text of
+the ::Message-id:: header that Exim creates if a
+locally-originated
+incoming message does not have one. The text of this header is required by RFC
+2822 to take the form of an address. By default, Exim uses its internal message
+id as the local part, and the primary host name as the domain. If this option
+is set, it is expanded, and provided the expansion is not forced to fail, and
+does not yield an empty string, the result is inserted into the header
+immediately before the @@, separated from the internal message id by a dot. Any
+characters that are illegal in an address are automatically converted into
+hyphens. This means that variables such as \$tod@_log$\ can be used, because
+the spaces and colons will become hyphens.
+
+.conf message@_logs boolean true
+.index message||log, disabling
+.index log||message log, disabling
+If this option is turned off, per-message log files are not created in the
+\(msglog)\ spool sub-directory. This reduces the amount of disk I/O required by
+Exim, by reducing the number of files involved in handling a message from a
+minimum of four (header spool file, body spool file, delivery journal, and
+per-message log) to three. The other major I/O activity is Exim's main log,
+which is not affected by this option.
+
+.conf message@_size@_limit string$**$ 50M
+.index message||size limit
+.index limit||message size
+.index size||of message, limit
+This option limits the maximum size of message that Exim will process. The
+value is expanded for each incoming
+connection so, for example, it can be made to depend on the IP address of the
+remote host for messages arriving via TCP/IP. \**Note**\: This limit cannot be
+made to depend on a message's sender or any other properties of an individual
+message, because it has to be advertised in the server's response to \\EHLO\\.
+String expansion failure causes a temporary error. A value of zero means no
+limit, but its use is not recommended. See also \bounce@_return@_size@_limit\.
+
+Incoming SMTP messages are failed with a 552 error if the limit is
+exceeded; locally-generated messages either get a stderr message or a delivery
+failure message to the sender, depending on the \-oe-\ setting. Rejection of an
+oversized message is logged in both the main and the reject logs. See also the
+generic transport option \message@_size@_limit\, which limits the size of
+message that an individual transport can process.
+
+.conf move@_frozen@_messages boolean false
+.index frozen messages||moving
+This option, which is available only if Exim has been built with the setting
+.display asis
+SUPPORT_MOVE_FROZEN_MESSAGES=yes
+.endd
+in \(Local/Makefile)\, causes frozen messages and their message logs to be
+moved from the \(input)\ and \(msglog)\ directories on the spool to \(Finput)\
+and \(Fmsglog)\, respectively. There is currently no support in Exim or the
+standard utilities for handling such moved messages, and they do not show up in
+lists generated by \-bp-\ or by the Exim monitor.
+
+.conf mysql@_servers "string list" unset
+.index MySQL||server list
+This option provides a list of MySQL servers and associated connection data, to
+be used in conjunction with \%mysql%\ lookups (see section ~~SECTsql). The
+option is available only if Exim has been built with MySQL support.
+
+.conf never@_users "string list" unset
+Local message deliveries are normally run in processes that are setuid to the
+recipient, and remote deliveries are normally run under Exim's own uid and gid.
+It is usually desirable to prevent any deliveries from running as root, as a
+safety precaution.
+
+When Exim is built, an option called \\FIXED@_NEVER@_USERS\\ can be set to a
+list of users that must not be used for local deliveries. This list is fixed in
+the binary and cannot be overridden by the configuration file. By default, it
+contains just the single user name `root'. The \never@_users\ runtime option
+can be used to add more users to the fixed list.
+
+If a message is to be delivered as one of the users on the fixed list or the
+\never@_users\ list, an error occurs, and delivery is deferred. A common
+example is
+.display
+never@_users = root:daemon:bin
+.endd
+Including root is redundant if it is also on the fixed list, but it does no
+harm.
+This option overrides the \pipe@_as@_creator\ option of the \%pipe%\ transport
+driver.
+
+.conf oracle@_servers "string list" unset
+.index Oracle||server list
+This option provides a list of Oracle servers and associated connection data,
+to be used in conjunction with \%oracle%\ lookups (see section ~~SECTsql). The
+option is available only if Exim has been built with Oracle support.
+
+.conf percent@_hack@_domains "domain list$**$" unset
+.index `percent hack'
+.index source routing||in email address
+.index address||source-routed
+The `percent hack' is the convention whereby a local part containing a percent
+sign is re-interpreted as a new email address, with the percent replaced by @@.
+This is sometimes called `source routing', though that term is also applied to
+RFC 2822 addresses that begin with an @@ character. If this option is set, Exim
+implements the percent facility for those domains listed, but no others. This
+happens before an incoming SMTP address is tested against an ACL.
+
+\**Warning**\: The `percent hack' has often been abused by people who are
+trying to get round relaying restrictions. For this reason, it is best avoided
+if at all possible. Unfortunately, a number of less security-conscious MTAs
+implement it unconditionally. If you are running Exim on a gateway host, and
+routing mail through to internal MTAs without processing the local parts, it is
+a good idea to reject recipient addresses with percent characters in their
+local parts. Exim's default configuration does this.
+
+.conf perl@_at@_start boolean false
+This option is available only when Exim is built with an embedded Perl
+interpreter. See chapter ~~CHAPperl for details of its use.
+
+.conf perl@_startup string unset
+This option is available only when Exim is built with an embedded Perl
+interpreter. See chapter ~~CHAPperl for details of its use.
+
+.conf pgsql@_servers "string list" unset
+.index PostgreSQL lookup type||server list
+This option provides a list of PostgreSQL servers and associated connection
+data, to be used in conjunction with \%pgsql%\ lookups (see section ~~SECTsql).
+The option is available only if Exim has been built with PostgreSQL support.
+
+.conf pid@_file@_path string$**$ "set at compile time"
+.index daemon||pid file path
+.index pid file, path for
+This option sets the name of the file to which the Exim daemon writes its
+process id. The string is expanded, so it can contain, for example, references
+to the host name:
+.display asis
+pid_file_path = /var/log/$primary_hostname/exim.pid
+.endd
+If no path is set, the pid is written to the file \(exim-daemon.pid)\ in Exim's
+spool directory.
+The value set by the option can be overridden by the \-oP-\ command line
+option. A pid file is not written if a `non-standard' daemon is run by means of
+the \-oX-\ option, unless a path is explicitly supplied by \-oP-\.
+
+.conf pipelining@_advertise@_hosts "host list$**$" $*$
+.index \\PIPELINING\\||advertising, suppressing
+This option can be used to suppress the advertisement of the SMTP
+\\PIPELINING\\ extension to specific hosts. When \\PIPELINING\\ is not
+advertised and \smtp@_enforce@_sync\ is true, an Exim server enforces strict
+synchronization for each SMTP command and response.
+.em
+When \\PIPELINING\\ is advertised, Exim assumes that clients will use it; `out
+of order' commands that are `expected' do not count as protocol errors (see
+\smtp@_max@_synprot@_errors\).
+.nem
+
+.conf preserve@_message@_logs boolean false
+.index message logs, preserving
+If this option is set, message log files are not deleted when messages are
+completed. Instead, they are moved to a sub-directory of the spool directory
+called \(msglog.OLD)\, where they remain available for statistical or debugging
+purposes. This is a dangerous option to set on systems with any appreciable
+volume of mail. Use with care!
+
+.conf primary@_hostname string "see below"
+.index name||of local host
+.index host||name of local
+.index local host||name of
+.em
+This specifies the name of the current host. It is used in the default \\EHLO\\
+or \\HELO\\ command for outgoing SMTP messages (changeable via the \helo@_data\
+option in the \%smtp%\ transport),
+.nem
+and as the default for \qualify@_domain\. If it is not set, Exim calls
+\*uname()*\ to find it. If this fails, Exim panics and dies. If the name
+returned by \*uname()*\ contains only one component, Exim passes it to
+\*gethostbyname()*\ (or \*getipnodebyname()*\ when available) in order to
+obtain the fully qualified version.
+
+.em
+The value of \$primary@_hostname$\ is also used by default in some SMTP
+response messages from an Exim server. This can be changed dynamically by
+setting \smtp@_active@_hostname\.
+.nem
+
+.conf print@_topbitchars boolean false
+.index printing characters
+.index 8-bit characters
+By default, Exim considers only those characters whose codes lie in the range
+32--126 to be printing characters. In a number of circumstances (for example,
+when writing log entries) non-printing characters are converted into escape
+sequences, primarily to avoid messing up the layout. If \print@_topbitchars\ is
+set, code values of 128 and above are also considered to be printing
+characters.
+
+.conf process@_log@_path string unset
+.index process log path
+.index log||process log
+.index \*exiwhat*\
+This option sets the name of the file to which an Exim process writes its
+`process log' when sent a USR1 signal. This is used by the \*exiwhat*\ utility
+script. If this option is unset, the file called \(exim-process.info)\ in
+Exim's spool directory is used. The ability to specify the name explicitly can
+be useful in environments where two different Exims are running, using
+different spool directories.
+
+.conf prod@_requires@_admin boolean true
+.index \-M-\ option
+.index \-R-\ option
+.index \-q-\ option
+The \-M-\, \-R-\, and \-q-\ command-line options require the caller to be an
+admin user unless \prod@_requires@_admin\ is set false. See also
+\queue@_list@_requires@_admin\.
+
+.conf qualify@_domain string "see below"
+.index domain||for qualifying addresses
+.index address||qualification
+This option specifies the domain name that is added to any sender addresses
+that do not have a domain qualification. It also applies to recipient addresses
+if \qualify@_recipient\ is not set. Such addresses are accepted by default only
+for locally-generated messages. Messages from external sources must always
+contain fully qualified addresses, unless the sending host matches
+\sender@_unqualified@_hosts\ or \recipient@_unqualified@_hosts\ (as
+appropriate), in which case incoming addresses are qualified with
+\qualify@_domain\ or \qualify@_recipient\ as necessary. Internally, Exim always
+works with fully qualified addresses.
+If \qualify@_domain\ is not set, it defaults to the \primary@_hostname\ value.
+
+.conf qualify@_recipient string "see below"
+This specifies the domain name that is added to any recipient addresses that do
+not have a domain qualification. Such addresses are accepted by default only
+for locally-generated messages. Messages from external sources must always
+contain fully qualified recipient addresses, unless the sending host matches
+\recipient@_unqualified@_hosts\,
+in which case incoming recipient addresses are qualified with
+\qualify@_recipient\.
+If \qualify@_recipient\ is not set, it defaults to the \qualify@_domain\ value.
+
+.conf queue@_domains "domain list$**$" unset
+.index domain||specifying non-immediate delivery
+.index queueing incoming messages
+.index message||queueing certain domains
+This option lists domains for which immediate delivery is not required.
+A delivery process is started whenever a message is received, but only those
+domains that do not match are processed. All other deliveries wait until the
+next queue run. See also \hold@_domains\ and \queue@_smtp@_domains\.
+
+.conf queue@_list@_requires@_admin boolean true
+.index \-bp-\ option
+The \-bp-\ command-line option, which lists the messages that are on the queue,
+requires the caller to be an admin user unless \queue__list__requires__admin\
+is set false. See also \prod@_requires@_admin\.
+
+.conf queue@_only boolean false
+.index queueing incoming messages
+.index message||queueing unconditionally
+If \queue@_only\ is set, a delivery process is not automatically started
+whenever a message is received. Instead, the message waits on the queue for the
+next queue run. Even if \queue@_only\ is false, incoming messages may not get
+delivered immediately when certain conditions (such as heavy load) occur.
+
+The \-odq-\ command line has the same effect as \queue@_only\. The \-odb-\ and
+\-odi-\ command line options override \queue@_only\ unless
+\queue@_only@_override\ is set false. See also \queue@_only@_file\,
+\queue@_only@_load\, and \smtp@_accept@_queue\.
+
+.conf queue@_only@_file string unset
+.index queueing incoming messages
+.index message||queueing by file existence
+This option can be set to a colon-separated list of absolute path names, each
+one optionally preceded by `smtp'. When Exim is receiving a message,
+it tests for the existence of each listed path using a call to \*stat()*\. For
+each path that exists, the corresponding queuing option is set.
+For paths with no prefix, \queue@_only\ is set; for paths prefixed by `smtp',
+\queue@_smtp@_domains\ is set to match all domains. So, for example,
+.display asis
+queue_only_file = smtp/some/file
+.endd
+causes Exim to behave as if \queue@_smtp@_domains\ were set to `$*$' whenever
+\(/some/file)\ exists.
+
+.conf queue@_only@_load fixed-point unset
+.index load average
+.index queueing incoming messages
+.index message||queueing by load
+If the system load average is higher than this value, incoming messages from
+all sources are queued, and no automatic deliveries are started. If this
+happens during local or remote SMTP input, all subsequent messages on the same
+connection are queued. Deliveries will subsequently be performed by queue
+runner processes. This option has no effect on ancient operating systems on
+which Exim cannot determine the load average. See also
+\deliver@_queue@_load@_max\ and \smtp@_load@_reserve\.
+
+.conf queue@_only@_override boolean true
+.index queueing incoming messages
+When this option is true, the \-od\*x*\-\ command line options override the
+setting of \queue@_only\ or \queue@_only@_file\ in the configuration file. If
+\queue@_only@_override\ is set false, the \-od\*x*\-\ options cannot be used to
+override; they are accepted, but ignored.
+
+.conf queue@_run@_in@_order boolean false
+.index queue runner||processing messages in order
+If this option is set, queue runs happen in order of message arrival instead of
+in an arbitrary order. For this to happen, a complete list of the entire queue
+must be set up before the deliveries start. When the queue is all in a single
+directory (the default), this happens anyway, but if \split@_spool@_directory\
+is set it does not -- for delivery in random order, the sub-directories are
+processed one at a time (in random order), to avoid setting up one huge list.
+Thus, setting \queue@_run@_in@_order\ with \split@_spool@_directory\ may
+degrade performance when the queue is large. In most situations,
+\queue@_run@_in@_order\ should not be set.
+
+.conf queue@_run@_max integer 5
+.index queue runner||maximum number of
+This controls the maximum number of queue runner processes that an Exim daemon
+can run simultaneously. This does not mean that it starts them all at once,
+but rather that if the maximum number are still running when the time comes to
+start another one, it refrains from starting another one. This can happen with
+very large queues and/or very sluggish deliveries. This option does not,
+however, interlock with other processes, so additional queue runners can be
+started by other means, or by killing and restarting the daemon.
+
+.conf queue@_smtp@_domains "domain list$**$" unset
+.index queueing incoming messages
+.index message||queueing remote deliveries
+When this option is set, a delivery process is started whenever a message is
+received, routing is performed, and local deliveries take place.
+However, if any SMTP deliveries are required for domains that match
+\queue@_smtp@_domains\, they are not immediately delivered, but instead the
+message waits on the queue for the next queue run. Since routing of the message
+has taken place, Exim knows to which remote hosts it must be delivered, and so
+when the queue run happens, multiple messages for the same host are delivered
+over a single SMTP connection. The \-odqs-\ command line option causes all SMTP
+deliveries to be queued in this way, and is equivalent to setting
+\queue@_smtp@_domains\ to `$*$'. See also \hold@_domains\ and \queue@_domains\.
+
+.conf receive@_timeout time 0s
+.index timeout||for non-SMTP input
+This option sets the timeout for accepting a non-SMTP message, that is, the
+maximum time that Exim waits when reading a message on the standard input. If
+the value is zero, it will wait for ever. This setting is overridden by the
+\-or-\ command line option. The timeout for incoming SMTP messages is
+controlled by \smtp@_receive@_timeout\.
+
+.index customizing|| ::Received:: header
+.index ::Received:: header line||customizing
+.conf received@_header@_text string$**$ "see below"
+This string defines the contents of the ::Received:: message header that is
+added to each message, except for the timestamp, which is automatically added
+on at the end (preceded by a semicolon). The string is expanded each time it is
+used. If the expansion yields an empty string, no ::Received:: header line is
+added to the message. Otherwise, the string should start with the text
+`Received:' and conform to the RFC 2822 specification for ::Received:: header
+lines. The default setting is:
+.display asis
+received_header_text = Received: \
+ ${if def:sender_rcvhost {from $sender_rcvhost\n\t}\
+ {${if def:sender_ident {from $sender_ident }}\
+ ${if def:sender_helo_name {(helo=$sender_helo_name)\n\t}}}}\
+ by $primary_hostname \
+ ${if def:received_protocol {with $received_protocol}} \
+ ${if def:tls_cipher {($tls_cipher)\n\t}}\
+ (Exim $version_number)\n\t\
+ id $message_id\
+ ${if def:received_for {\n\tfor $received_for}}
+.endd
+Note the use of quotes, to allow the sequences \"@\n"\ and \"@\t"\ to be used
+for newlines and tabs, respectively. The reference to the TLS cipher is omitted
+when Exim is built without TLS support. The use of conditional expansions
+ensures that this works for both locally generated messages and messages
+received from remote hosts, giving header lines such as the following:
+.display asis
+Received: from scrooge.carol.example ([192.168.12.25] ident=root)
+ by marley.carol.example with esmtp (Exim 4.00)
+ id 16IOWa-00019l-00
+ for chas@dickens.example; Tue, 25 Dec 2001 14:43:44 +0000
+Received: by scrooge.carol.example with local (Exim 4.00)
+ id 16IOWW-000083-00; Tue, 25 Dec 2001 14:43:41 +0000
+.endd
+.em
+Until the body of the message has been received, the timestamp is the time when
+the message started to be received. Once the body has arrived, and all policy
+checks have taken place, the timestamp is updated to the time at which the
+message was accepted.
+.nem
+
+.conf received@_headers@_max integer 30
+.index loop||prevention
+.index mail loop prevention
+.index ::Received:: header line||counting
+When a message is to be delivered, the number of ::Received:: headers is
+counted, and if it is greater than this parameter, a mail loop is assumed to
+have occurred, the delivery is abandoned, and an error message is generated.
+This applies to both local and remote deliveries.
+
+.conf recipient@_unqualified@_hosts "host list$**$" unset
+.index unqualified addresses
+.index host||unqualified addresses from
+This option lists those hosts from which Exim is prepared to accept unqualified
+recipient addresses in message envelopes. The addresses are made fully
+qualified by the addition of the \qualify@_recipient\ value. This option also
+affects message header lines. Exim does not reject unqualified recipient
+addresses in headers, but it qualifies them only if the message came from a
+host that matches \recipient@_unqualified@_hosts\,
+.em
+or if the message was submitted locally (not using TCP/IP), and the \-bnq-\
+option was not set.
+.nem
+
+.conf recipients@_max integer 0
+.index limit||number of recipients
+.index recipient||maximum number
+If this option is set greater than zero, it specifies the maximum number of
+original recipients for any message. Additional recipients that are generated
+by aliasing or forwarding do not count. SMTP messages get a 452 response for
+all recipients over the limit; earlier recipients are delivered as normal.
+Non-SMTP messages with too many recipients are failed, and no deliveries are
+done.
+.index \\RCPT\\||maximum number of incoming
+Note that the RFCs specify that an SMTP server should accept at least 100
+\\RCPT\\ commands in a single message.
+
+.conf recipients@_max@_reject boolean false
+If this option is set true, Exim rejects SMTP messages containing too many
+recipients by giving 552 errors to the surplus \\RCPT\\ commands, and a 554
+error to the eventual \\DATA\\ command. Otherwise (the default) it gives a 452
+error to the surplus \\RCPT\\ commands and accepts the message on behalf of the
+initial set of recipients. The remote server should then re-send the message
+for the remaining recipients at a later time.
+
+.conf remote@_max@_parallel integer 2
+.index delivery||parallelism for remote
+This option controls parallel delivery of one message to a number of remote
+hosts. If the value is less than 2, parallel delivery is disabled, and Exim
+does all the remote deliveries for a message one by one. Otherwise, if a single
+message has to be delivered to more than one remote host, or if several copies
+have to be sent to the same remote host, up to \remote@_max@_parallel\
+deliveries are done simultaneously. If more than \remote@_max@_parallel\
+deliveries are required, the maximum number of processes are started, and as
+each one finishes, another is begun. The order of starting processes is the
+same as if sequential delivery were being done, and can be controlled by the
+\remote@_sort@_domains\ option. If parallel delivery takes place while running
+with debugging turned on, the debugging output from each delivery process is
+tagged with its process id.
+
+This option controls only the maximum number of parallel deliveries for one
+message in one Exim delivery process. Because Exim has no central queue
+manager, there is no way of controlling the total number of simultaneous
+deliveries if the configuration allows a delivery attempt as soon as a message
+is received.
+.index number of deliveries
+.index delivery||maximum number of
+If you want to control the total number of deliveries on the system, you
+need to set the \queue@_only\ option. This ensures that all incoming messages
+are added to the queue without starting a delivery process. Then set up an Exim
+daemon to start queue runner processes at appropriate intervals (probably
+fairly often, for example, every minute), and limit the total number of queue
+runners by setting the \queue__run__max\ parameter. Because each queue runner
+delivers only one message at a time, the maximum number of deliveries that can
+then take place at once is \queue@_run@_max\ multiplied by
+\remote@_max@_parallel\.
+
+If it is purely remote deliveries you want to control, use \queue@_smtp\
+instead of \queue@_only\. This has the added benefit of doing the SMTP routing
+before queuing, so that several messages for the same host will eventually get
+delivered down the same connection.
+
+.conf remote@_sort@_domains "domain list$**$" unset
+.index sorting remote deliveries
+.index delivery||sorting remote
+When there are a number of remote deliveries for a message, they are sorted by
+domain into the order given by this list. For example,
+.display asis
+remote_sort_domains = *.cam.ac.uk:*.uk
+.endd
+would attempt to deliver to all addresses in the \*cam.ac.uk*\ domain first, then
+to those in the \uk\ domain, then to any others.
+
+.conf retry@_data@_expire time 7d
+.index hints database||data expiry
+This option sets a `use before' time on retry information in Exim's hints
+database. Any older retry data is ignored. This means that, for example, once a
+host has not been tried for 7 days, Exim behaves as if it has no knowledge of
+past failures.
+
+.conf retry@_interval@_max time 24h
+.index retry||limit on interval
+.index limit||on retry interval
+Chapter ~~CHAPretry describes Exim's mechanisms for controlling the intervals
+between delivery attempts for messages that cannot be delivered straight away.
+This option sets an overall limit to the length of time between retries.
+
+.conf return@_path@_remove boolean true
+.index ::Return-path:: header line||removing
+RFC 2821, section 4.4, states that an SMTP server must insert a ::Return-path::
+header line into a message when it makes a `final delivery'. The ::Return-path::
+header preserves the sender address as received in the \\MAIL\\ command. This
+description implies that this header should not be present in an incoming
+message. If \return@_path@_remove\ is true, any existing ::Return-path::
+headers are removed from messages at the time they are received. Exim's
+transports have options for adding ::Return-path:: headers at the time of
+delivery. They are normally used only for final local deliveries.
+
+.conf return@_size@_limit integer 100K
+This option is an obsolete synonym for \bounce@_return@_size@_limit\.
+
+.conf rfc1413@_hosts "host list$**$" $*$
+.index RFC 1413
+.index host||for RFC 1413 calls
+RFC 1413 identification calls are made to any client host which matches an item
+in the list.
+
+.conf rfc1413@_query@_timeout time 30s
+.index RFC 1413||query timeout
+.index timeout||for RFC 1413 call
+This sets the timeout on RFC 1413 identification calls. If it is set to zero,
+no RFC 1413 calls are ever made.
+
+.conf sender@_unqualified@_hosts "host list$**$" unset
+.index unqualified addresses
+.index host||unqualified addresses from
+This option lists those hosts from which Exim is prepared to accept unqualified
+sender addresses. The addresses are made fully qualified by the addition of
+\qualify@_domain\. This option also affects message header lines. Exim does not
+reject unqualified addresses in headers that contain sender addresses, but it
+qualifies them only if the message came from a host that matches
+\sender@_unqualified@_hosts\,
+.em
+or if the message was submitted locally (not using TCP/IP), and the \-bnq-\
+option was not set.
+.nem
+
+.conf smtp@_accept@_keepalive boolean true
+.index keepalive||on incoming connection
+This option controls the setting of the \\SO@_KEEPALIVE\\ option on incoming
+TCP/IP socket connections. When set, it causes the kernel to probe idle
+connections periodically, by sending packets with `old' sequence numbers. The
+other end of the connection should send an acknowledgement if the connection is
+still okay or a reset if the connection has been aborted. The reason for doing
+this is that it has the beneficial effect of freeing up certain types of
+connection that can get stuck when the remote host is disconnected without
+tidying up the TCP/IP call properly. The keepalive mechanism takes several
+hours to detect unreachable hosts.
+
+
+.conf smtp@_accept@_max integer 20
+.index limit||incoming SMTP connections
+.index SMTP||incoming connection count
+.index inetd
+This option specifies the maximum number of simultaneous incoming SMTP calls
+that Exim will accept. It applies only to the listening daemon; there is no
+control (in Exim) when incoming SMTP is being handled by \*inetd*\. If the value
+is set to zero, no limit is applied. However, it is required to be non-zero if
+either \smtp@_accept@_max@_per@_host\ or \smtp@_accept@_queue\ is set. See also
+\smtp@_accept@_reserve\.
+
+
+.conf smtp@_accept@_max@_nonmail integer 10
+.index limit||non-mail SMTP commands
+.index SMTP||limiting non-mail commands
+Exim counts the number of `non-mail' commands in an SMTP session, and drops the
+connection if there are too many. This option defines `too many'. The check
+catches some denial-of-service attacks, repeated failing \\AUTH\\s, or a mad
+client looping sending \\EHLO\\, for example. The check is applied only if the
+client host matches \smtp@_accept@_max@_nonmail@_hosts\.
+
+When a new message is expected, one occurrence of \\RSET\\ is not counted. This
+allows a client to send one \\RSET\\ between messages (this is not necessary,
+but some clients do it). Exim also allows one uncounted occurence of \\HELO\\
+or \\EHLO\\, and one occurrence of \\STARTTLS\\ between messages. After
+starting up a TLS session, another \\EHLO\\ is expected, and so it too is not
+counted. The first occurrence of \\AUTH\\ in a connection, or immediately
+following \\STARTTLS\\ is not counted. Otherwise, all commands other than
+\\MAIL\\, \\RCPT\\, \\DATA\\, and \\QUIT\\ are counted.
+
+.conf smtp@_accept@_max@_nonmail@_hosts "host list$**$" $*$
+You can control which hosts are subject to the \smtp@_accept@_max@_nonmail\
+check by setting this option. The default value makes it apply to all hosts. By
+changing the value, you can exclude any badly-behaved hosts that you have to
+live with.
+
+
+.conf smtp@_accept@_max@_per@_connection integer 1000
+.index SMTP||incoming message count, limiting
+.index limit||messages per SMTP connection
+The value of this option limits the number of \\MAIL\\ commands that Exim is
+prepared to accept over a single SMTP connection, whether or not each command
+results in the transfer of a message. After the limit is reached, a 421
+response is given to subsequent \\MAIL\\ commands. This limit is a safety
+precaution against a client that goes mad (incidents of this type have been
+seen).
+
+.conf smtp@_accept@_max@_per@_host string$**$ unset
+.index limit||SMTP connections from one host
+.index host||limiting SMTP connections from
+This option restricts the number of simultaneous IP connections from a single
+host (strictly, from a single IP address) to the Exim daemon. The option is
+expanded, to enable different limits to be applied to different hosts by
+reference to \$sender@_host@_address$\. Once the limit is reached, additional
+connection attempts from the same host are rejected with error code 421. The
+default value of zero imposes no limit. If this option is set, it is required
+that \smtp@_accept@_max\ be non-zero.
+
+\**Warning**\: When setting this option you should not use any expansion
+constructions that take an appreciable amount of time. The expansion and test
+happen in the main daemon loop, in order to reject additional connections
+without forking additional processes (otherwise a denial-of-service attack
+could cause a vast number or processes to be created). While the daemon is
+doing this processing, it cannot accept any other incoming connections.
+
+
+.conf smtp@_accept@_queue integer 0
+.index SMTP||incoming connection count
+.index queueing incoming messages
+.index message||queueing by SMTP connection count
+If the number of simultaneous incoming SMTP calls handled via the listening
+daemon exceeds this value, messages received by SMTP are just placed on the
+queue; no delivery processes are started automatically. A value of zero implies
+no limit, and clearly any non-zero value is useful only if it is less than the
+\smtp@_accept@_max\ value (unless that is zero). See also \queue@_only\,
+\queue@_only@_load\, \queue@_smtp@_domains\, and the various \-od-\ command
+line options.
+
+.conf smtp@_accept@_queue@_per@_connection integer 10
+.index queueing incoming messages
+.index message||queueing by message count
+This option limits the number of delivery processes that Exim starts
+automatically when receiving messages via SMTP, whether via the daemon or by
+the use of \-bs-\ or \-bS-\. If the value of the option is greater than zero,
+and the number of messages received in a single SMTP session exceeds this
+number, subsequent messages are placed on the queue, but no delivery processes
+are started. This helps to limit the number of Exim processes when a server
+restarts after downtime and there is a lot of mail waiting for it on other
+systems. On large systems, the default should probably be increased, and on
+dial-in client systems it should probably be set to zero (that is, disabled).
+
+.conf smtp@_accept@_reserve integer 0
+.index SMTP||incoming call count
+.index host||reserved
+When \smtp@_accept@_max\ is set greater than zero, this option specifies a
+number of SMTP connections that are reserved for connections from the hosts
+that are specified in \smtp@_reserve@_hosts\. The value set in
+\smtp@_accept@_max\ includes this reserve pool. The specified hosts are not
+restricted to this number of connections; the option specifies a minimum number
+of connection slots for them, not a maximum. It is a guarantee that that group
+of hosts can always get at least \smtp@_accept@_reserve\ connections.
+
+For example, if \smtp@_accept@_max\ is set to 50 and \smtp@_accept@_reserve\ is
+set to 5, once there are 45 active connections (from any hosts), new
+connections are accepted only from hosts listed in \smtp@_reserve@_hosts\.
+See also \smtp@_accept@_max@_per@_host\.
+
+.em
+.conf smtp@_active@_hostname string$**$ unset
+.index host||name in SMTP responses
+.index SMTP||host name in responses
+This option is provided for multi-homed servers that want to masquerade as
+several different hosts. At the start of an SMTP connection, its value is
+expanded and used instead of the value of \$primary@_hostname$\ in SMTP
+responses. For example, it is used as domain name in the response to an
+incoming \\HELO\\ or \\EHLO\\ command. If this option is unset, or if its
+expansion is forced to fail, or if the expansion results in an empty string,
+the value of \$primary@_hostname$\ is used. Other expansion failures cause a
+message to be written to the main and panic logs, and the SMTP command receives
+a temporary error. Typically, the value of \smtp@_active@_hostname\ depends on
+the incoming interface address. For example:
+.display asis
+smtp_active_hostname = ${if eq{$interface_address}{10.0.0.1}\
+ {cox.mydomain}{box.mydomain}}
+.endd
+If you set \smtp@_active@_hostname\, you probably also want to set
+\smtp@_banner\, since its default value references \$primary@_hostname$\.
+.nem
+
+.conf smtp@_banner string$**$ "see below"
+.index SMTP||welcome banner
+.index banner for SMTP
+.index welcome banner for SMTP
+.index customizing||SMTP banner
+This string, which is expanded every time it is used, is output as the initial
+positive response to an SMTP connection. The default setting is:
+.display asis
+smtp_banner = $primary_hostname ESMTP Exim $version_number \
+ $tod_full
+.endd
+Failure to expand the string causes a panic error. If you want to create a
+multiline response to the initial SMTP connection, use `@\n' in the string at
+appropriate points, but not at the end. Note that the 220 code is not included
+in this string. Exim adds it automatically (several times in the case of a
+multiline response).
+
+.conf smtp@_check@_spool@_space boolean true
+.index checking disk space
+.index disk space, checking
+.index spool directory||checking space
+When this option is set, if an incoming SMTP session encounters the \\SIZE\\
+option on a \\MAIL\\ command, it checks that there is enough space in the
+spool directory's partition to accept a message of that size, while still
+leaving free the amount specified by \check@_spool@_space\ (even if that value
+is zero). If there isn't enough space, a temporary error code is returned.
+
+.conf smtp@_connect@_backlog integer 20
+.index connection backlog
+.index SMTP||connection backlog
+.index backlog of connections
+This option specifies a maximum number of waiting SMTP connections. Exim passes
+this value to the TCP/IP system when it sets up its listener. Once this number
+of connections are waiting for the daemon's attention, subsequent connection
+attempts are refused at the TCP/IP level. At least, that is what the manuals
+say; in some circumstances such connection attempts have been observed to time
+out instead. For large systems it is probably a good idea to increase the
+value (to 50, say). It also gives some protection against denial-of-service
+attacks by SYN flooding.
+
+.conf smtp@_enforce@_sync boolean true
+.index SMTP||synchronization checking
+.index synchronization checking in SMTP
+The SMTP protocol specification requires the client to wait for a response from
+the server at certain points in the dialogue. Without \\PIPELINING\\ these
+synchronization points are after every command; with \\PIPELINING\\ they are
+fewer, but they still exist. Some spamming sites send out a complete set of
+SMTP commands without waiting for any response. Exim protects against this by
+rejecting a message if the client has sent further input when it should not
+have. The error response `554 SMTP synchronization error' is sent, and the
+connection is dropped. Testing for this error cannot be perfect because of
+transmission delays (unexpected input may be on its way but not yet received
+when Exim checks). However, it does detect many instances. The check can be
+disabled by setting \smtp@_enforce@_sync\ false.
+.em
+See also \pipelining@_advertise@_hosts\.
+.nem
+
+.conf smtp@_etrn@_command string$**$ unset
+.index \\ETRN\\||command to be run
+If this option is set, the given command is run whenever an SMTP \\ETRN\\
+command is received from a host that is permitted to issue such commands (see
+chapter ~~CHAPACL). The string is split up into separate arguments which are
+independently expanded. The expansion variable \$domain$\ is set to the
+argument of the \\ETRN\\ command, and no syntax checking is done on it. For
+example:
+.display asis
+smtp_etrn_command = /etc/etrn_command $domain $sender_host_address
+.endd
+A new process is created to run the command, but Exim does not wait for it to
+complete. Consequently, its status cannot be checked. If the command cannot be
+run, a line is written to the panic log, but the \\ETRN\\ caller still receives
+a 250 success response. Exim is normally running under its own uid when
+receiving SMTP, so it is not possible for it to change the uid before running
+the command.
+
+.conf smtp@_etrn@_serialize boolean true
+.index \\ETRN\\||serializing
+When this option is set, it prevents the simultaneous execution of more than
+one identical command as a result of \\ETRN\\ in an SMTP connection. See
+section ~~SECTETRN for details.
+
+.conf smtp@_load@_reserve fixed-point unset
+.index load average
+If the system load average ever gets higher than this, incoming SMTP calls are
+accepted only from those hosts that match an entry in \smtp@_reserve@_hosts\.
+If \smtp@_reserve@_hosts\ is not set, no incoming SMTP calls are accepted when
+the load is over the limit. The option has no effect on ancient operating
+systems on which Exim cannot determine the load average. See also
+\deliver@_queue@_load@_max\ and \queue@_only@_load\.
+
+
+.conf smtp@_max@_synprot@_errors integer 3
+.index SMTP||limiting syntax and protocol errors
+.index limit||SMTP syntax and protocol errors
+Exim rejects SMTP commands that contain syntax or protocol errors. In
+particular, a syntactically invalid email address, as in this command:
+.display asis
+RCPT TO:<abc xyz@a.b.c>
+.endd
+causes immediate rejection of the command, before any other tests are done.
+(The ACL cannot be run if there is no valid address to set up for it.) An
+example of a protocol error is receiving \\RCPT\\ before \\MAIL\\. If there are
+too many syntax or protocol errors in one SMTP session, the connection is
+dropped. The limit is set by this option.
+
+.em
+.index \\PIPELINING\\||expected errors
+When the \\PIPELINING\\ extension to SMTP is in use, some protocol errors are
+`expected', for instance, a \\RCPT\\ command after a rejected \\MAIL\\ command.
+Exim assumes that \\PIPELINING\\ will be used if it advertises it (see
+\pipelining@_advertise@_hosts\), and in this situation, `expected' errors do
+not count towards the limit.
+.nem
+
+
+.conf smtp@_max@_unknown@_commands integer 3
+.index SMTP||limiting unknown commands
+.index limit||unknown SMTP commands
+If there are too many unrecognized commands in an incoming SMTP session, an
+Exim server drops the connection. This is a defence against some kinds of abuse
+that subvert web
+.em
+clients
+.nem
+into making connections to SMTP ports; in these circumstances, a number of
+non-SMTP command lines are sent first.
+
+
+.conf smtp@_ratelimit@_hosts "host list$**$" unset
+.index SMTP||rate limiting
+.index limit||rate of message arrival
+.index \\RCPT\\||rate limiting
+Some sites find it helpful to be able to limit the rate at which certain hosts
+can send them messages, and the rate at which an individual message can specify
+recipients. When a host matches \smtp@_ratelimit@_hosts\, the values of
+\smtp@_ratelimit@_mail\ and \smtp@_ratelimit@_rcpt\ are used to control the
+rate of acceptance of \\MAIL\\ and \\RCPT\\ commands in a single SMTP session,
+respectively. Each option, if set, must contain a set of four comma-separated
+values:
+.numberpars $.
+A threshold, before which there is no rate limiting.
+.nextp
+An initial time delay. Unlike other times in Exim, numbers with decimal
+fractional parts are allowed here.
+.nextp
+A factor by which to increase the delay each time.
+.nextp
+A maximum value for the delay. This should normally be less than 5 minutes,
+because after that time, the client is liable to timeout the SMTP command.
+.endp
+For example, these settings have been used successfully at the site which
+first suggested this feature, for controlling mail from their customers:
+.display asis
+smtp_ratelimit_mail = 2,0.5s,1.05,4m
+smtp_ratelimit_rcpt = 4,0.25s,1.015,4m
+.endd
+The first setting specifies delays that are applied to \\MAIL\\ commands after
+two have been received over a single connection. The initial delay is 0.5
+seconds, increasing by a factor of 1.05 each time. The second setting applies
+delays to \\RCPT\\ commands when more than four occur in a single message.
+
+It is also possible to configure delays explicitly in ACLs. See section
+~~SECTACLmodi for details.
+
+
+.conf smtp@_ratelimit@_mail string unset
+See \smtp@_ratelimit@_hosts\ above.
+
+.conf smtp@_ratelimit@_rcpt string unset
+See \smtp@_ratelimit@_hosts\ above.
+
+.conf smtp@_receive@_timeout time 5m
+.index timeout||for SMTP input
+.index SMTP||timeout, input
+This sets a timeout value for SMTP reception. It applies to all forms of SMTP
+input, including batch SMTP. If a line of input (either an SMTP command or a
+data line) is not received within this time, the SMTP connection is dropped and
+the message is abandoned.
+A line is written to the log containing one of the following messages:
+.display asis
+SMTP command timeout on connection from...
+SMTP data timeout on connection from...
+.endd
+The former means that Exim was expecting to read an SMTP command; the latter
+means that it was in the \\DATA\\ phase, reading the contents of a message.
+
+
+.index \-os-\ option
+The value set by this option can be overridden by the
+\-os-\ command-line option. A setting of zero time disables the timeout, but
+this should never be used for SMTP over TCP/IP. (It can be useful in some cases
+of local input using \-bs-\ or \-bS-\.) For non-SMTP input, the reception
+timeout is controlled by \receive@_timeout\ and \-or-\.
+
+.conf smtp@_reserve@_hosts "host list$**$" unset
+This option defines hosts for which SMTP connections are reserved; see
+\smtp@_accept@_reserve\ and \smtp@_load@_reserve\ above.
+
+.conf smtp@_return@_error@_details boolean false
+.index SMTP||details policy failures
+.index policy control||rejection, returning details
+In the default state, Exim uses bland messages such as
+`Administrative prohibition' when it rejects SMTP commands for policy
+reasons. Many sysadmins like this because it gives away little information
+to spammers. However, some other syadmins who are applying strict checking
+policies want to give out much fuller information about failures. Setting
+\smtp@_return@_error@_details\ true causes Exim to be more forthcoming. For
+example, instead of `Administrative prohibition', it might give:
+.display asis
+550-Rejected after DATA: '>' missing at end of address:
+550 failing address in "From" header is: <user@dom.ain
+.endd
+
+.conf split@_spool@_directory boolean false
+.index multiple spool directories
+.index spool directory||split
+.index directories, multiple
+If this option is set, it causes Exim to split its input directory into 62
+subdirectories, each with a single alphanumeric character as its name. The
+sixth character of the message id is used to allocate messages to
+subdirectories; this is the least significant base-62 digit of the time of
+arrival of the message.
+
+Splitting up the spool in this way may provide better performance on systems
+where there are long mail queues, by reducing the number of files in any one
+directory. The msglog directory is also split up in a similar way to the input
+directory; however, if \preserve@_message@_logs\ is set, all old msglog files
+are still placed in the single directory \(msglog.OLD)\.
+
+It is not necessary to take any special action for existing messages when
+changing \split@_spool@_directory\. Exim notices messages that are in the
+`wrong' place, and continues to process them. If the option is turned off after
+a period of being on, the subdirectories will eventually empty and be
+automatically deleted.
+
+When \split@_spool@_directory\ is set, the behaviour of queue runner processes
+changes. Instead of creating a list of all messages in the queue, and then
+trying to deliver each one in turn, it constructs a list of those in one
+sub-directory and tries to deliver them, before moving on to the next
+sub-directory. The sub-directories are processed in a random order. This
+spreads out the scanning of the input directories, and uses less memory. It is
+particularly beneficial when there are lots of messages on the queue. However,
+if \queue@_run@_in@_order\ is set, none of this new processing happens. The
+entire queue has to be scanned and sorted before any deliveries can start.
+
+.conf spool@_directory string$**$ "set at compile time"
+.index spool directory||path to
+This defines the directory in which Exim keeps its spool, that is, the messages
+it is waiting to deliver. The default value is taken from the compile-time
+configuration setting, if there is one. If not, this option must be set. The
+string is expanded, so it can contain, for example, a reference to
+\$primary@_hostname$\.
+
+If the spool directory name is fixed on your installation, it is recommended
+that you set it at build time rather than from this option, particularly if the
+log files are being written to the spool directory (see \log@_file@_path\).
+Otherwise log files cannot be used for errors that are detected early on, such
+as failures in the configuration file.
+
+By using this option to override the compiled-in path, it is possible to run
+tests of Exim without using the standard spool.
+
+.conf strip@_excess@_angle@_brackets boolean false
+.index angle brackets, excess
+If this option is set, redundant pairs of angle brackets round `route-addr'
+items in addresses are stripped. For example, \*@<@<xxx@@a.b.c.d@>@>*\ is treated
+as \*@<xxx@@a.b.c.d@>*\. If this is in the envelope and the message is passed on
+to another MTA, the excess angle brackets are not passed on. If this option is
+not set, multiple pairs of angle brackets cause a syntax error.
+
+.conf strip@_trailing@_dot boolean false
+.index trailing dot on domain
+.index dot||trailing on domain
+If this option is set, a trailing dot at the end of a domain in an address is
+ignored. If this is in the envelope and the message is passed on to another
+MTA, the dot is not passed on. If this option is not set, a dot at the end of a
+domain causes a syntax error.
+.em
+However, addresses in header lines are checked only when an ACL requests header
+syntax checking.
+.nem
+
+.conf syslog@_duplication boolean true
+.index syslog||duplicate log lines, suppressing
+When Exim is logging to syslog, it writes the log lines for its three
+separate logs at different syslog priorities so that they can in principle
+be separated on the logging hosts. Some installations do not require this
+separation, and in those cases, the duplication of certain log lines is a
+nuisance. If \syslog@_duplication\ is set false, only one copy of any
+particular log line is written to syslog. For lines that normally go to
+both the main log and the reject log, the reject log version (possibly
+containing message header lines) is written, at \\LOG@_NOTICE\\ priority.
+Lines that normally go to both the main and the panic log are written at
+the \\LOG@_ALERT\\ priority.
+
+.conf syslog@_facility string unset
+.index syslog||facility, setting
+This option sets the syslog `facility' name, used when Exim is logging to
+syslog. The value must be one of the strings `mail', `user', `news', `uucp',
+`daemon', or `local\*x*\' where \*x*\ is a digit between 0 and 7. If this
+option is unset, `mail' is used. See chapter ~~CHAPlog for details of Exim's
+logging.
+
+
+.conf syslog@_processname string "$tt{exim}"
+.index syslog||process name, setting
+This option sets the syslog `ident' name, used when Exim is logging to syslog.
+The value must be no longer than 32 characters. See chapter ~~CHAPlog for
+details of Exim's logging.
+
+
+.conf syslog@_timestamp boolean true
+.index syslog||timestamps
+If \syslog@_timestamp\ is set false, the timestamps on Exim's log lines are
+omitted when these lines are sent to syslog. See chapter ~~CHAPlog for
+details of Exim's logging.
+
+.conf system@_filter string$**$ unset
+.index filter||system filter
+.index system filter||specifying
+.index Sieve filter||not available for system filter
+This option specifies an Exim filter file that is applied to all messages at
+the start of each delivery attempt, before any routing is done. System filters
+must be Exim filters; they cannot be Sieve filters. If the system filter
+generates any deliveries to files or pipes, or any new mail messages, the
+appropriate \system@_filter@_...@_transport\ option(s) must be set, to define
+which transports are to be used. Details of this facility are given in chapter
+~~CHAPsystemfilter.
+
+.conf system@_filter@_directory@_transport string$**$ unset
+This sets the name of the transport driver that is to be used when the
+\save\ command in a system message filter specifies a path ending in `/',
+implying delivery of each message into a separate file in some directory.
+During the delivery, the variable \$address@_file$\ contains the path name.
+
+.conf system@_filter@_file@_transport string$**$ unset
+.index file||transport for system filter
+This sets the name of the transport driver that is to be used when the \save\
+command in a system message filter specifies a path not ending in `/'. During
+the delivery, the variable \$address@_file$\ contains the path name.
+
+.index gid (group id)||system filter
+.conf system@_filter@_group string unset
+This option is used only when \system@_filter@_user\ is also set. It sets the
+gid under which the system filter is run, overriding any gid that is associated
+with the user. The value may be numerical or symbolic.
+
+.conf system@_filter@_pipe@_transport string$**$ unset 7
+.index \%pipe%\ transport||for system filter
+This specifies the transport driver that is to be used when a \pipe\ command is
+used in a system filter. During the delivery, the variable \$address@_pipe$\
+contains the pipe command.
+
+.conf system@_filter@_reply@_transport string$**$ unset
+.index \%autoreply%\ transport||for system filter
+This specifies the transport driver that is to be used when a \mail\ command is
+used in a system filter.
+
+.index uid (user id)||system filter
+.conf system@_filter@_user string unset
+If this option is not set, the system filter is run in the main Exim delivery
+process, as root. When the option is set, the system filter runs in a separate
+process, as the given user. Unless the string consists entirely of digits, it
+is looked up in the password data. Failure to find the named user causes a
+configuration error. The gid is either taken from the password data, or
+specified by \system@_filter@_group\. When the uid is specified numerically,
+\system@_filter@_group\ is required to be set.
+
+If the system filter generates any pipe, file, or reply deliveries, the uid
+under which the filter is run is used when transporting them, unless a
+transport option overrides.
+Normally you should set \system@_filter@_user\ if your system filter generates
+these kinds of delivery.
+
+.conf tcp@_nodelay boolean true
+.index daemon||\\TCP@_NODELAY\\ on sockets
+.index Nagle algorithm
+.index \\TCP@_NODELAY\\ on listening sockets
+If this option is set false, it stops the Exim daemon setting the
+\\TCP@_NODELAY\\ option on its listening sockets. Setting \\TCP@_NODELAY\\
+turns off the `Nagle algorithm', which is a way of improving network
+performance in interactive (character-by-character) situations. Turning it off
+should improve Exim's performance a bit, so that is what happens by default.
+However, it appears that some broken clients cannot cope, and time out. Hence
+this option. It affects only those sockets that are set up for listening by the
+daemon. Sockets created by the smtp transport for delivering mail always set
+\\TCP@_NODELAY\\.
+
+.conf timeout@_frozen@_after time 0s
+.index frozen messages||timing out
+.index timeout||frozen messages
+If \timeout@_frozen@_after\ is set to a time greater than zero, a frozen
+message of any kind that has been on the queue for longer than the given
+time is automatically cancelled at the next queue run. If it is a bounce
+message, it is just discarded; otherwise, a bounce is sent to the sender, in a
+similar manner to cancellation by the \-Mg-\ command line option. If you want
+to timeout frozen bounce messages earlier than other kinds of frozen message,
+see \ignore@_bounce@_errors@_after\.
+
+.conf timezone string unset
+.index timezone, setting
+The value of \timezone\ is used to set the environment variable \\TZ\\ while
+running Exim (if it is different on entry). This ensures that all timestamps
+created by Exim are in the required timezone. If you want all your timestamps
+to be in UTC (aka GMT) you should set
+.display asis
+timezone = UTC
+.endd
+The default value is taken from \\TIMEZONE@_DEFAULT\\ in \(Local/Makefile)\,
+or, if that is not set, from the value of the TZ environment variable when Exim
+is built. If \timezone\ is set to the empty string, either at build or run
+time, any existing \\TZ\\ variable is removed from the environment when Exim
+runs. This is appropriate behaviour for obtaining wall-clock time on some, but
+unfortunately not all, operating systems.
+
+.conf tls@_advertise@_hosts "host list$**$" unset
+.index TLS||advertising
+.index encryption||on SMTP connection
+.index SMTP||encrypted connection
+When Exim is built with support for TLS encrypted connections, the availability
+of the \\STARTTLS\\ command to set up an encrypted session is advertised in
+response to \\EHLO\\ only to those client hosts that match this option. See
+chapter ~~CHAPTLS for details of Exim's support for TLS.
+
+.conf tls@_certificate string$**$ unset
+.index TLS||server certificate, location of
+.index certificate||for server, location of
+The value of this option is expanded, and must then be the absolute path to a
+file which contains the server's certificates. The server's private key is also
+assumed to be in this file if \tls@_privatekey\ is unset. See chapter ~~CHAPTLS
+for further details.
+
+\**Note**\: The certificates defined by this option are used only when Exim is
+receiving incoming messages as a server. If you want to supply certificates for
+use when sending messages as a client, you must set the \tls@_certificate\
+option in the relevant \%smtp%\ transport.
+
+.em
+.conf tls@_crl string$**$ unset
+.index TLS||server certificate revocation list
+.index certificate||revocation list for server
+This option specifies a certificate revocation list. The expanded value must
+be the name of a file that contains a CRL in PEM format.
+.nem
+
+.conf tls@_dhparam string$**$ unset
+.index TLS||D-H parameters for server
+The value of this option is expanded, and must then be the absolute path to
+a file which contains the server's DH parameter values.
+This is used only for OpenSSL. When Exim is linked with GnuTLS, this option is
+ignored. See section ~~SECTopenvsgnu for further details.
+
+.conf tls@_privatekey string$**$ unset
+.index TLS||server private key, location of
+The value of this option is expanded, and must then be the absolute path to
+a file which contains the server's private key.
+If this option is unset, the private key is assumed to be in the same file as
+the server's certificates. See chapter ~~CHAPTLS for further details.
+
+.conf tls@_remember@_esmtp boolean false
+.index TLS||esmtp state, remembering
+.index TLS||broken clients
+If this option is set true, Exim violates the RFCs by remembering that it is in
+`esmtp' state after successfully negotiating a TLS session. This provides
+support for broken clients that fail to send a new \\EHLO\\ after starting a
+TLS session.
+
+.em
+.conf tls@_require@_ciphers string$**$ unset
+.index TLS||requiring specific ciphers
+.index cipher||requiring specific
+This option controls which ciphers can be used for incoming TLS connections.
+(The \%smtp%\ transport has an option of the same name for controlling outgoing
+connections.) This option is expanded for each connection, so can be varied for
+different clients if required. The value of this option must be a list of
+permitted cipher suites. The OpenSSL and GnuTLS libraries handle cipher control
+in somewhat different ways. Details are given in section ~~SECTreqciphsslgnu.
+.nem
+
+.conf tls@_try@_verify@_hosts "host list$**$" unset
+.index TLS||client certificate verification
+.index certificate||verification of client
+See \tls@_verify@_hosts\ below.
+
+.conf tls@_verify@_certificates string$**$ unset
+.index TLS||client certificate verification
+.index certificate||verification of client
+The value of this option is expanded, and must then be the absolute path to
+a file containing permitted certificates for clients that
+match \tls@_verify@_hosts\ or \tls@_try@_verify@_hosts\. Alternatively, if you
+are using OpenSSL, you can set \tls@_verify@_certificates\ to the name of a
+directory containing certificate files. This does not work with GnuTLS; the
+option must be set to the name of a single file if you are using GnuTLS.
+
+.conf tls@_verify@_hosts "host list$**$" unset
+.index TLS||client certificate verification
+.index certificate||verification of client
+This option, along with \tls@_try@_verify@_hosts\, controls the checking of
+certificates from clients.
+The expected certificates are defined by \tls@_verify@_certificates\, which
+must be set. A configuration error occurs if either \tls@_verify@_hosts\ or
+\tls@_try@_verify@_hosts\ is set and \tls@_verify@_certificates\ is not set.
+
+Any client that matches \tls@_verify@_hosts\ is constrained by
+\tls@_verify@_certificates\. The client must present one of the listed
+certificates. If it does not, the connection is aborted.
+
+A weaker form of checking is provided by \tls@_try@_verify@_hosts\. If a client
+matches this option (but not \tls@_verify@_hosts\), Exim requests a
+certificate and checks it against \tls@_verify@_certificates\, but does not
+abort the connection if there is no certificate or if it does not match. This
+state can be detected in an ACL, which makes it possible to implement policies
+such as `accept for relay only if a verified certificate has been received, but
+accept for local delivery if encrypted, even without a verified certificate'.
+
+Client hosts that match neither of these lists are not asked to present
+certificates.
+
+.conf trusted@_groups "string list" unset
+.index trusted group
+.index group||trusted
+If this option is set, any process that is running in one of the listed groups,
+or which has one of them as a supplementary group, is trusted.
+The groups can be specified numerically or by name.
+See section ~~SECTtrustedadmin for details of what trusted callers are
+permitted to do. If neither \trusted@_groups\ nor \trusted@_users\ is set, only
+root and the Exim user are trusted.
+
+.conf trusted@_users "string list" unset
+.index trusted user
+.index user||trusted
+If this option is set, any process that is running as one of the listed users
+is trusted.
+The users can be specified numerically or by name.
+See section ~~SECTtrustedadmin for details of what trusted callers are
+permitted to do. If neither \trusted@_groups\ nor \trusted@_users\ is set, only
+root and the Exim user are trusted.
+
+.index uid (user id)||unknown caller
+.conf unknown@_login string$**$ unset
+This is a specialized feature for use in unusual configurations. By default, if
+the uid of the caller of Exim cannot be looked up using \*getpwuid()*\, Exim
+gives up. The \unknown@_login\ option can be used to set a login name to be
+used in this circumstance. It is expanded, so values like \user@$caller@_uid\
+can be set. When \unknown@_login\ is used, the value of \unknown@_username\ is
+used for the user's real name (gecos field), unless this has been set by the
+\-F-\ option.
+
+.conf unknown@_username string unset
+See \unknown@_login\.
+
+.conf untrusted@_set@_sender "address list$**$" unset
+.index trusted user
+.index sender||setting by untrusted user
+.index untrusted user, setting sender
+.index user||untrusted setting sender
+.index envelope sender
+When an untrusted user submits a message to Exim using the standard input, Exim
+normally creates an envelope sender address from the user's login and the
+default qualification domain. Data from the \-f-\ option (for setting envelope
+senders on non-SMTP messages) or the SMTP \\MAIL\\ command (if \-bs-\ or \-bS-\
+is used) is ignored.
+
+However, untrusted users are permitted to set an empty envelope sender address,
+to declare that a message should never generate any bounces. For example:
+.display asis
+exim -f '<>' user@domain.example
+.endd
+The \untrusted@_set@_sender\ option allows you to permit untrusted users to set
+other envelope sender addresses in a controlled way. When it is set, untrusted
+users are allowed to set envelope sender addresses that match any of the
+patterns in the list. Like all address lists, the string is expanded. The
+identity of the user is in \$sender@_ident$\, so you can, for example, restrict
+users to setting senders that start with their login ids
+followed by a hyphen
+by a setting like this:
+.display asis
+untrusted_set_sender = ^$sender_ident-
+.endd
+If you want to allow untrusted users to set envelope sender addresses without
+restriction, you can use
+.display asis
+untrusted_set_sender = *
+.endd
+The \untrusted@_set@_sender\ option applies to all forms of local input, but
+only to the setting of the envelope sender. It does not permit untrusted users
+to use the other options which trusted user can use to override message
+parameters. Furthermore, it does not stop Exim from removing an existing
+::Sender:: header in the message, or from adding a ::Sender:: header if
+necessary. See \local__sender__retain\ and \local@_from@_check\ for ways of
+overriding these actions. The handling of the ::Sender:: header is also
+described in section ~~SECTthesenhea.
+
+The log line for a message's arrival shows the envelope sender following `<='.
+For local messages, the user's login always follows, after `U='. In \-bp-\
+displays, and in the Exim monitor, if an untrusted user sets an envelope sender
+address, the user's login is shown in parentheses after the sender address.
+
+.conf uucp@_from@_pattern string "see below"
+.index `From' line
+.index UUCP||`From' line
+Some applications that pass messages to an MTA via a command line interface use
+an initial line starting with `From' to pass the envelope sender. In
+particular, this is used by UUCP software. Exim recognizes such a line by means
+of a regular expression that is set in \uucp@_from@_pattern\. When the pattern
+matches, the sender address is constructed by expanding the contents of
+\uucp@_from@_sender\, provided that the caller of Exim is a trusted user. The
+default pattern recognizes lines in the following two forms:
+.display asis
+ From ph10 Fri Jan 5 12:35 GMT 1996
+ From ph10 Fri, 7 Jan 97 14:00:00 GMT
+.endd
+The pattern can be seen by running
+.display asis
+exim -bP uucp_from_pattern
+.endd
+It checks only up to the hours and minutes, and allows for a 2-digit or 4-digit
+year in the second case. The first word after `From' is matched in the regular
+expression by a parenthesized subpattern. The default value for
+\uucp@_from@_sender\ is `$1', which therefore just uses this first word (`ph10'
+in the example above) as the message's sender. See also
+\ignore@_fromline@_hosts\.
+
+.conf uucp@_from@_sender string$**$ "$tt{@$1}"
+See \uucp@_from@_pattern\ above.
+
+.conf warn@_message@_file string unset
+.index warning of delay||customizing the message
+.index customizing||warning message
+This option defines a template file containing paragraphs of text to be used
+for constructing the warning message which is sent by Exim when a message has
+been on the queue for a specified amount of time, as specified by
+\delay@_warning\. Details of the file's contents are given in chapter
+~~CHAPemsgcust. See also \bounce@_message@_file\.
+
+.em
+.conf write@_rejectlog boolean true
+.index reject log||disabling
+If this option is set false, Exim no longer writes anything to the reject log.
+See chapter ~~CHAPlog for details of what Exim writes to its logs.
+.nem
+
+.endconf
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Generic options for routers
+.rset CHAProutergeneric "~~chapter"
+.set runningfoot "generic router options"
+.index options||generic, for routers
+.index generic options||router
+
+This chapter describes the generic options that apply to all routers,
+identifying those that are preconditions. For a general description of how a
+router operates, see sections ~~SECTrunindrou and ~~SECTrouprecon. The second
+of these sections specifies the order in which the preconditions are tested.
+The order of expansion of the options that provide data for a transport is:
+\errors@_to\, \headers@_add\, \headers@_remove\, \transport\.
+
+.startconf
+
+.conf address@_data string$**$ unset
+.index router||data attached to address
+The string is expanded just before the router is run, that is, after all the
+precondition tests have succeeded. If the expansion is forced to fail, the
+router declines. Other expansion failures cause delivery of the address to be
+deferred.
+
+When the expansion succeeds, the value is retained with the address, and can be
+accessed using the variable \$address@_data$\ in the current router, subsequent
+routers, and the eventual transport.
+
+\**Warning**\: if the current or any subsequent router is a \%redirect%\ router
+that runs a user's filter file, the contents of \$address@_data$\ are
+accessible in the filter. This is not normally a problem, because such data is
+usually either not confidential or it `belongs' to the current user, but if you
+do put confidential data into \$address@_data$\ you need to remember this
+point.
+
+Even if the router declines or passes, the value of \$address@_data$\ remains
+with the address, though it can be changed by another \address@_data\ setting
+on a subsequent router. If a router generates child addresses, the value of
+\$address@_data$\ propagates to them. This also applies to the special kind of
+`child' that is generated by a router with the \unseen\ option.
+
+The idea of \address@_data\ is that you can use it to look up a lot of data for
+the address once, and then pick out parts of the data later. For example, you
+could use a single LDAP lookup to return a string of the form
+.display asis
+uid=1234 gid=5678 mailbox=/mail/xyz forward=/home/xyz/.forward
+.endd
+In the transport you could pick out the mailbox by a setting such as
+.display asis
+file = ${extract{mailbox}{$address_data}}
+.endd
+This makes the configuration file less messy, and also reduces the number of
+lookups. (Exim does cache the most recent lookup, but there may be several
+addresses in a message which cause lookups to occur.)
+
+The \address@_data\ facility is also useful as a means of passing information
+from one router to another,
+and from a router to a transport. In addition, if \address@_data\ is set by a
+router when verifying an address from an ACL, its value is available for use in
+the rest of the ACL statement.
+
+
+.conf address@_test "boolean (precondition)" true
+.index \-bt-\ option
+.index router||skipping when address testing
+If this option is set false, the router is skipped when routing is being tested
+by means of the \-bt-\ command line option. This can be a convenience when your
+first router sends messages to an external scanner, because it saves you
+having to set the `already scanned' indicator when testing real address
+routing.
+
+
+.conf cannot@_route@_message string$**$ unset
+.index router||customizing `cannot route' message
+.index customizing||`cannot route' message
+This option specifies a text message that is used when an address cannot be
+routed because Exim has run out of routers. The default message is `Unrouteable
+address'. This option is useful only on routers that have \more\ set false, or
+on the very last router in a configuration, because the value that is used is
+taken from the last router that inspects an address. For example, using the
+default configuration, you could put:
+.display asis
+cannot_route_message = Remote domain not found in DNS
+.endd
+on the first (\%dnslookup%\) router, and
+.display asis
+cannot_route_message = Unknown local user
+.endd
+on the final router that checks for local users. If string expansion fails, the
+default message is used.
+Unless the expansion failure was explicitly forced, a message about the failure
+is written to the main and panic logs, in addition to the normal message about
+the routing failure.
+
+.conf caseful@_local@_part boolean false
+.index case of local parts
+.index router||case of local parts
+By default, routers handle the local parts of addresses in a case-insensitive
+manner, though the actual case is preserved for transmission with the message.
+If you want the case of letters to be significant in a router, you must set
+this option true. For individual router options that contain address or local
+part lists (for example, \local@_parts\), case-sensitive matching can be turned
+on by `+caseful' as a list item. See section ~~SECTcasletadd for more details.
+
+
+.conf check@_local@_user "boolean (precondition)" false
+.index local user, checking in router
+.index router||checking for local user
+When this option is true, Exim checks that the local part of the recipient
+address (with affixes removed if relevant) is the name of an account on the
+local system. The check is done by calling the \*getpwnam()*\ function rather
+than trying to read \(/etc/passwd)\ directly. This means that other methods of
+holding password data (such as NIS) are supported. If the local part is a local
+user, \$home$\ is set from the password data, and can be tested in other
+preconditions that are evaluated after this one
+(the order of evaluation is given in section ~~SECTrouprecon). However, the
+value of \$home$\ can be overridden by \router@_home@_directory\.
+If the local part is not a local user, the router is skipped.
+
+If you want to check that the local part is either the name of a local user
+or matches something else, you cannot combine \check@_local@_user\ with a
+setting of \local@_parts\, because that specifies the logical \*and*\ of the
+two conditions. However, you can use a \%passwd%\ lookup in a \local@_parts\
+setting to achieve this. For example:
+.display asis
+local_parts = passwd;$local_part : lsearch;/etc/other/users
+.endd
+Note, however, that the side effects of \check@_local@_user\ (such as setting
+up a home directory) do not occur when a \%passwd%\ lookup is used in a
+\local@_parts\ (or any other) precondition.
+
+.conf condition "string$**$ (precondition)" unset
+.index router||customized precondition
+This option specifies a general precondition test that has to succeed for the
+router to be called. The string is expanded, and if the result is a forced
+failure or an empty string or one of the strings `0' or `no' or `false'
+(checked without regard to the case of the letters), the router is skipped, and
+the address is offered to the next one. This provides a means of applying
+special-purpose conditions to the running of routers.
+
+If the expansion fails (other than forced failure) delivery is deferred. Some
+of the other options below are common special cases that could in fact be
+specified using \condition\.
+Note that \condition\ is the last precondition to be evaluated (see
+section ~~SECTrouprecon).
+
+
+.conf debug@_print string$**$ unset
+.index testing||variables in drivers
+If this option is set and debugging is enabled (see the \-d-\ command line
+option), the string is expanded and included in the debugging output.
+If expansion of the string fails, the error message is written to the debugging
+output, and Exim carries on processing.
+This option is provided to help with checking out the values of variables and
+so on when debugging router configurations. For example, if a \condition\
+option appears not to be working, \debug@_print\ can be used to output the
+variables it references. The output happens after checks for \domains\,
+\local@_parts\, and \check@_local@_user\ but before any other preconditions are
+tested. A newline is added to the text if it does not end with one.
+
+
+.conf disable@_logging boolean false
+If this option is set true, nothing is logged for any routing errors
+.em
+or for any deliveries caused by this router. You should not set this option
+unless you really, really know what you are doing. See also the generic
+transport option of the same name.
+.nem
+
+.conf domains "domain list$**$ (precondition)" unset
+.index router||restricting to specific domains
+If this option is set, the router is skipped unless the current domain matches
+the list. If the match is achieved by means of a file lookup, the data that the
+lookup returned for the domain is placed in \$domain@_data$\ for use in string
+expansions of the driver's private options.
+See section ~~SECTrouprecon for a list of the order in which preconditions
+are evaluated.
+
+
+.conf driver string unset
+This option must always be set. It specifies which of the available routers is
+to be used.
+
+
+.conf errors@_to string$**$ unset
+.index envelope sender
+.index router||changing address for errors
+If a router successfully handles an address, it may queue the address for
+delivery or it may generate child addresses. In both cases, if there is a
+delivery problem during later processing, the resulting bounce message is sent
+to the address that results from expanding this string, provided that the
+address verifies successfully.
+\errors@_to\ is expanded before \headers@_add\, \headers@_remove\, and
+\transport\.
+
+If the option is unset, or the expansion is forced to fail, or the result of
+the expansion fails to verify, the errors address associated with the incoming
+address is used. At top level, this is the envelope sender. A non-forced
+expansion failure causes delivery to be deferred.
+
+If an address for which \errors@_to\ has been set ends up being delivered over
+SMTP, the envelope sender for that delivery is the \errors@_to\ value, so that
+any bounces that are generated by other MTAs on the delivery route are also
+sent there. The most common use of \errors@_to\ is probably to direct mailing
+list bounces to the manager of the list, as described in section
+~~SECTmailinglists.
+
+The \errors@_to\ setting associated with an address can be overridden if it
+subsequently passes through other routers that have their own \errors@_to\
+settings,
+or if it is delivered by a transport with a \return@_path\ setting.
+
+You can set \errors@_to\ to the empty string by either of these settings:
+.display asis
+errors_to =
+errors_to = ""
+.endd
+An expansion item that yields an empty string has the same effect. If you do
+this, a locally detected delivery error for addresses processed by this router
+no longer gives rise to a bounce message; the error is discarded. If the
+address is delivered to a remote host, the return path is set to \"<>"\, unless
+overridden by the \return@_path\ option on the transport.
+
+If for some reason you want to discard local errors, but use a non-empty
+\\MAIL\\ command for remote delivery, you can preserve the original return
+path in \$address@_data$\ in the router, and reinstate it in the transport by
+setting \return@_path\.
+
+
+.conf expn "boolean (precondition)" true
+.index address||testing
+.index testing||addresses
+.index \\EXPN\\||router skipping
+.index router||skipping for \\EXPN\\
+If this option is turned off, the router is skipped when testing an address
+as a result of processing an SMTP \\EXPN\\ command. You might, for example,
+want to turn it off on a router for users' \(.forward)\ files, while leaving it
+on for the system alias file.
+See section ~~SECTrouprecon for a list of the order in which preconditions
+are evaluated.
+
+The use of the SMTP \\EXPN\\ command is controlled by an ACL (see chapter
+~~CHAPACL). When Exim is running an \\EXPN\\ command, it is similar to testing
+an address with \-bt-\. Compare \\VRFY\\, whose counterpart is \-bv-\.
+
+
+.conf fail@_verify boolean false
+.index router||forcing verification failure
+Setting this option has the effect of setting both \fail@_verify@_sender\ and
+\fail@_verify@_recipient\ to the same value.
+
+
+.conf fail@_verify@_recipient boolean false
+If this option is true and an address is accepted by this router when
+verifying a recipient, verification fails.
+
+
+.conf fail@_verify@_sender boolean false
+If this option is true and an address is accepted by this router when
+verifying a sender, verification fails.
+
+
+.conf fallback@_hosts "string list" unset
+.index router||fallback hosts
+.index fallback||hosts specified on router
+String expansion is not applied to this option. The argument must be a
+colon-separated list of host names or IP addresses. If a router queues an
+address for a remote transport, this host list is associated with the address,
+and used instead of the transport's fallback host list. If \hosts@_randomize\
+is set on the transport, the order of the list is randomized for each use. See
+the \fallback@_hosts\ option of the \%smtp%\ transport for further details.
+
+.conf group string$**$ "see below"
+.index gid (group id)||local delivery
+.index local transports||uid and gid
+.index transport||local
+.index router||setting group
+When a router queues an address for a transport, and the transport does not
+specify a group, the group given here is used when running the delivery
+process.
+The group may be specified numerically or by name. If expansion fails, the
+error is logged and delivery is deferred.
+The default is unset, unless \check@_local@_user\ is set, when the default
+is taken from the password information. See also \initgroups\ and \user\ and
+the discussion in chapter ~~CHAPenvironment.
+
+
+.conf headers@_add string$**$ unset
+.index header lines||adding
+.index router||adding header lines
+This option specifies a string of text that is expanded at routing time, and
+associated with any addresses that are processed by the router
+when delivering a message. This option has no effect when an address is just
+being verified.
+
+The \headers@_add\ option is expanded after \errors@_to\, but before
+\headers@_remove\ and \transport\.
+If the expanded string is empty, or if the expansion is forced to fail, the
+option has no effect. Other expansion failures are treated as configuration
+errors. The expanded string must be in the form of one or more RFC 2822 header
+lines, separated by newlines (coded as `@\n'). For example:
+.display asis
+headers_add = X-added-header: added by $primary_hostname\n\
+ X-added-second: another added header line
+.endd
+Exim does not check the syntax of these added header lines. If an address
+passes through several routers as a result of aliasing or forwarding
+operations, any \headers@_add\ or \headers@_remove\ specifications are
+cumulative. This does not apply for multiple routers that result from the use
+of `unseen'.
+
+At transport time, all the original headers listed in \headers__remove\ are
+removed. If there are multiple instances of any listed header, they are all
+removed.
+Then the new headers specified by \headers@_add\ are added, in the order in
+which they were attached to the address. Finally, any additional headers
+specified by the transport are added. It is not possible to remove headers
+added to an address by \headers@_add\.
+
+Because the addition does not happen until transport time, header lines that
+are added by \headers@_add\ are not accessible by means of the \$header@_xxx$\
+expansion syntax. Conversely, header lines that are removed by
+\headers@_remove\ remain visible.
+
+Addresses with different \headers@_add\ or \headers@_remove\ settings cannot be
+delivered together in a batch. The \headers@_add\ option cannot be used for a
+\%redirect%\ router that has the \one@_time\ option set.
+
+
+.conf headers@_remove string$**$ unset
+.index header lines||removing
+.index router||removing header lines
+The string is expanded at routing time and is then associated with any
+addresses that are processed by the router when delivering a message. This
+option has no effect when an address is being verified. The \headers@_remove\
+option is expanded after \errors@_to\ and \headers@_add\, but before
+\transport\. If the expansion is forced to fail, the option has no effect.
+Other expansion failures are treated as configuration errors.
+
+.em
+After expansion, the string must consist of a colon-separated list of header
+names. This is confusing, because header names themselves are often terminated
+by colons. In this case, the colons are the list separators, not part of the
+names.
+.nem
+For example:
+.display asis
+headers_remove = return-receipt-to:acknowledge-to
+.endd
+The list is used at transport time as described under \headers@_add\ above. The
+\headers@_remove\ option cannot be used for a \%redirect%\ router that has the
+\one@_time\ option set.
+
+.conf ignore@_target@_hosts "host list$**$" unset
+.index IP address||discarding
+.index router||discarding IP addresses
+Although this option is a host list, it should normally contain IP address
+entries rather than names. If any host that is looked up by the router has an
+IP address that matches an item in this list, Exim behaves as if that IP
+address did not exist. This option allows you to cope with rogue DNS entries
+like
+.display asis
+remote.domain.example. A 127.0.0.1
+.endd
+by setting
+.display asis
+ignore_target_hosts = 127.0.0.1
+.endd
+on the relevant router.
+.em
+If all the hosts found by a \%dnslookup%\ router are discarded in this way, the
+router declines. In a conventional configuration, an attempt to mail to such a
+domain would then normally provoke the `unrouteable domain' error, and an
+attempt to verify an address in the domain would fail.
+
+Similarly, if \ignore@_target@_hosts\ is set on an \%ipliteral%\ router, the
+router declines if presented with one of the listed addresses.
+.nem
+
+This option may also be useful for ignoring link-local and site-local IPv6
+addresses. Because, like all host lists, the value of \ignore@_target@_hosts\
+is expanded before use as a list, it is possible to make it dependent on the
+domain that is being routed.
+
+
+
+.index additional groups
+.index groups, additional
+.index local transports||uid and gid
+.index transport||local
+.conf initgroups boolean false
+If the router queues an address for a transport, and this option is true, and
+the uid supplied by the router is not overridden by the transport, the
+\*initgroups()*\ function is called when running the transport to ensure that
+any additional groups associated with the uid are set up. See also \group\ and
+\user\ and the discussion in chapter ~~CHAPenvironment.
+
+
+.conf local@_part@_prefix "string list (precondition)" unset
+.index router||prefix for local part
+.index prefix||for local part, used in router
+If this option is set, the router is skipped unless the local part
+starts with one of the given strings, or \local@_part@_prefix@_optional\ is
+true.
+See section ~~SECTrouprecon for a list of the order in which preconditions
+are evaluated.
+
+The list is scanned from left to right, and the first prefix that matches is
+used. A limited form of wildcard is available; if the prefix begins with an
+asterisk, it matches the longest possible sequence of arbitrary characters at
+the start of the local part. An asterisk should therefore always be followed by
+some character that does not occur in normal local parts.
+.index multiple mailboxes
+.index mailbox||multiple
+Wildcarding can be used to set up multiple user mailboxes, as described in
+section ~~SECTmulbox.
+
+During the testing of the \local@_parts\ option, and while the router is
+running, the prefix is removed from the local part, and is available in the
+expansion variable \$local@_part@_prefix$\. If the router accepts the address,
+this remains true during subsequent delivery.
+In particular, the local part that is transmitted in the \\RCPT\\ command
+for LMTP, SMTP, and BSMTP deliveries has the prefix removed by default. This
+behaviour can be overridden by setting \rcpt@_include@_affixes\ true on the
+relevant transport.
+
+The prefix facility is commonly used to handle local parts of the form
+\owner-something\. Another common use is to support local parts of the form
+\real-username\ to bypass a user's \(.forward)\ file -- helpful when trying to
+tell a user their forwarding is broken -- by placing a router like this one
+immediately before the router that handles \(.forward)\ files:
+.display asis
+real_localuser:
+ driver = accept
+ local_part_prefix = real-
+ check_local_user
+ transport = local_delivery
+.endd
+If both \local@_part@_prefix\ and \local@_part@_suffix\ are set for a router,
+both conditions must be met if not optional. Care must be taken if wildcards
+are used in both a prefix and a suffix on the same router. Different
+separator characters must be used to avoid ambiguity.
+
+.conf local@_part@_prefix@_optional boolean false
+See \local@_part@_prefix\ above.
+
+
+.conf local@_part@_suffix "string list (precondition)" unset
+.index router||suffix for local part
+.index suffix for local part, used in router
+This option operates in the same way as \local@_part@_prefix\, except that the
+local part must end (rather than start) with the given string, the
+\local@_part@_suffix@_optional\ option determines whether the suffix is
+mandatory, and the wildcard $*$ character, if present, must be the last
+character of the suffix. This option facility is commonly used to handle local
+parts of the form \something-request\ and multiple user mailboxes of the form
+\username-foo\.
+
+.conf local@_part@_suffix@_optional boolean false
+See \local@_part@_suffix\ above.
+
+
+.conf local@_parts "local part list$**$ (precondition)" unset
+.index router||restricting to specific local parts
+.index local part||checking in router
+The router is run only if the local part of the address matches the list.
+See section ~~SECTrouprecon for a list of the order in which preconditions
+are evaluated, and
+section ~~SECTlocparlis for a discussion of local part lists. Because the
+string is expanded, it is possible to make it depend on the domain, for
+example:
+.display asis
+local_parts = dbm;/usr/local/specials/$domain
+.endd
+If the match is achieved by a lookup, the data that the lookup returned
+for the local part is placed in the variable \$local@_part@_data$\ for use in
+expansions of the router's private options. You might use this option, for
+example, if you have a large number of local virtual domains, and you want to
+send all postmaster mail to the same place without having to set up an alias in
+each virtual domain:
+.display asis
+postmaster:
+ driver = redirect
+ local_parts = postmaster
+ data = postmaster@real.domain.example
+.endd
+
+
+.conf log@_as@_local boolean "see below"
+.index log||delivery line
+.index delivery||log line format
+Exim has two logging styles for delivery, the idea being to make local
+deliveries stand out more visibly from remote ones. In the `local' style, the
+recipient address is given just as the local part, without a domain. The use of
+this style is controlled by this option. It defaults to true for the \%accept%\
+router, and false for all the others.
+
+
+.conf more boolean$**$ true
+The result of string expansion for this option must be a valid boolean value,
+that is, one of the strings `yes', `no', `true', or `false'. Any other result
+causes an error, and delivery is deferred. If the expansion is forced to fail,
+the default value for the option (true) is used. Other failures cause delivery
+to be deferred.
+
+If this option is set false, and the router is run, but declines to handle the
+address, no further routers are tried, routing fails, and the address is
+bounced.
+.index \self\ option
+However, if the router explicitly passes an address to the following router by
+means of the setting
+.display asis
+self = pass
+.endd
+or otherwise, the setting of \more\ is ignored. Also, the setting of \more\
+does not affect the behaviour if one of the precondition tests fails. In that
+case, the address is always passed to the next router.
+
+
+.conf pass@_on@_timeout boolean false
+.index timeout||of router
+.index router||timeout
+If a router times out during a host lookup, it normally causes deferral of the
+address. If \pass@_on@_timeout\ is set, the address is passed on to the next
+router, overriding \no@_more\. This may be helpful for systems that are
+intermittently connected to the Internet, or those that want to pass to a smart
+host any messages that cannot immediately be delivered.
+
+There are occasional other temporary errors that can occur while doing DNS
+lookups. They are treated in the same way as a timeout, and this option
+applies to all of them.
+
+
+.conf pass@_router string unset
+.index router||go to after `pass'
+When a router returns `pass', the address is normally handed on to the next
+router in sequence. This can be changed by setting \pass@_router\ to the name
+of another router. However (unlike \redirect@_router\) the named router must be
+below the current router, to avoid loops. Note that this option applies only to
+the special case of `pass'. It does not apply when a router returns `decline'.
+
+
+.conf redirect@_router string unset
+.index router||start at after redirection
+Sometimes an administrator knows that it is pointless to reprocess addresses
+generated from alias or forward files with the same router again. For
+example, if an alias file translates real names into login ids there is no
+point searching the alias file a second time, especially if it is a large file.
+
+The \redirect@_router\ option can be set to the name of any router instance. It
+causes the routing of any generated addresses to start at the named router
+instead of at the first router. This option has no effect if the router in
+which it is set does not generate new addresses.
+
+
+.conf require@_files "string list$**$ (precondition)" unset
+.index file||requiring for router
+.index router||requiring file existence
+This option provides a general mechanism for predicating the running of a
+router on the existence or non-existence of certain files or directories.
+Before running a router, as one of its precondition tests, Exim works its way
+through the \require@_files\ list, expanding each item separately.
+
+Because the list is split before expansion, any colons in expansion items must
+be doubled, or the facility for using a different list separator must be used.
+If any expansion is forced to fail, the item is ignored. Other expansion
+failures cause routing of the address to be deferred.
+
+If any expanded string is empty, it is ignored. Otherwise, except as described
+below, each string must be a fully qualified file path, optionally preceded by
+`!'. The paths are passed to the \*stat()*\ function to test for the existence
+of the files or directories. The router is skipped if any paths not preceded by
+`!' do not exist, or if any paths preceded by `!' do exist.
+
+.index NFS
+If \*stat()*\ cannot determine whether a file exists or not, delivery of
+the message is deferred. This can happen when NFS-mounted filesystems are
+unavailable.
+
+This option is checked after the \domains\, \local@_parts\, and \senders\
+options, so you cannot use it to check for the existence of a file in which to
+look up a domain, local part, or sender. (See section ~~SECTrouprecon for a
+full list of the order in which preconditions are evaluated.) However, as
+these options are all expanded, you can use the \exists\ expansion condition to
+make such tests. The \require@_files\ option is intended for checking files
+that the router may be going to use internally, or which are needed by a
+transport (for example \(.procmailrc)\).
+
+During delivery, the \*stat()*\ function is run as root, but there is a
+facility for some checking of the accessibility of a file by another user.
+This is not a proper permissions check, but just a `rough' check that
+operates as follows:
+
+If an item in a \require@_files\ list does not contain any forward slash
+characters, it is taken to be the user (and optional group, separated by a
+comma) to be checked for subsequent files in the list. If no group is specified
+but the user is specified symbolically, the gid associated with the uid is
+used. For example:
+.display asis
+require_files = mail:/some/file
+require_files = $local_part:$home/.procmailrc
+.endd
+If a user or group name in a \require@_files\ list does not exist, the
+\require@_files\ condition fails.
+
+Exim performs the check by scanning along the components of the file path, and
+checking the access for the given uid and gid. It checks for `x' access on
+directories, and `r' access on the final file. Note that this means that file
+access control lists, if the operating system has them, are ignored.
+
+\**Warning 1**\: When the router is being run to verify addresses for an
+incoming SMTP message, Exim is not running as root, but under its own uid. This
+may affect the result of a \require@_files\ check. In particular, \*stat()*\
+may yield the error \\EACCES\\ (`Permission denied'). This means that the Exim
+user is not permitted to read one of the directories on the file's path.
+
+\**Warning 2**\: Even when Exim is running as root while delivering a message,
+\*stat()*\ can yield \\EACCES\\ for a file on an NFS directory that is mounted
+without root access.
+
+In both cases,
+the default action is to consider this a configuration error, and routing is
+deferred because the existence or non-existence of the file cannot be
+determined. However, in some circumstances it may be desirable to treat this
+condition as if the file did not exist. If the file name (or the exclamation
+mark that precedes the file name for non-existence) is preceded by a plus sign,
+the \\EACCES\\ error is treated as if the file did not exist. For example:
+.display asis
+require_files = +/some/file
+.endd
+If the router is not an essential part of verification (for example, it
+handles users' \(.forward)\ files), another solution is to set the \verify\
+option false so that the router is skipped when verifying.
+
+
+.conf retry@_use@_local@_part boolean "see below"
+.index hints database||retry keys
+.index local part||in retry keys
+When a delivery suffers a temporary routing failure, a retry record is created
+in Exim's hints database. For addresses whose routing depends only on the
+domain, the key for the retry record should not involve the local part, but for
+other addresses, both the domain and the local part should be included.
+Usually, remote routing is of the former kind, and local routing is of the
+latter kind.
+
+This option controls whether the local part is used to form the key for retry
+hints for addresses that suffer temporary errors while being handled by this
+router. The default value is true for any router that has \check@_local@_user\
+set, and false otherwise. Note that this option does not apply to hints keys
+for transport delays; they are controlled by a generic transport option of the
+same name.
+
+.em
+The setting of \retry@_use@_local@_part\ applies only to the router on which it
+appears. If the router generates child addresses, they are routed
+independently; this setting does not become attached to them.
+.nem
+
+
+.conf router@_home@_directory string$**$ unset
+.index router||home directory for
+.index home directory||for router
+This option sets a home directory for use while the router is running. (Compare
+\transport__home@_directory\, which sets a home directory for later
+transporting.) In particular, if used on a \%redirect%\ router, this option
+sets a value for \$home$\ while a filter is running. The value is expanded;
+forced expansion failure causes the option to be ignored -- other failures
+cause the router to defer.
+
+Expansion of \router@_home@_directory\ happens immediately after the
+\check@_local@_user\ test (if configured), before any further expansions take
+place.
+(See section ~~SECTrouprecon for a list of the order in which preconditions
+are evaluated.)
+While the router is running, \router__home@_directory\ overrides the value of
+\$home$\ that came from \check@_local@_user\.
+
+When a router accepts an address and routes it to a transport (including the
+cases when a redirect router generates a pipe, file, or autoreply delivery),
+the home directory setting for the transport is taken from the first of these
+values that is set:
+.numberpars $.
+The \home@_directory\ option on the transport;
+.nextp
+The \transport@_home@_directory\ option on the router;
+.nextp
+The password data if \check@_local@_user\ is set on the router;
+.nextp
+The \router@_home@_directory\ option on the router.
+.endp
+In other words, \router@_home@_directory\ overrides the password data for the
+router, but not for the transport.
+
+
+.conf self string "freeze"
+.index MX record||pointing to local host
+.index local host||MX pointing to
+This option applies to those routers that use a recipient address to find a
+list of remote hosts. Currently, these are the \%dnslookup%\, \%ipliteral%\,
+and \%manualroute%\ routers.
+Certain configurations of the \%queryprogram%\ router can also specify a list
+of remote hosts.
+Usually such routers are configured to send the message to a remote host via an
+\%smtp%\ transport. The \self\ option specifies what happens when the first
+host on the list turns out to be the local host.
+The way in which Exim checks for the local host is described in section
+~~SECTreclocipadd.
+
+Normally this situation indicates either an error in Exim's configuration (for
+example, the router should be configured not to process this domain), or an
+error in the DNS (for example, the MX should not point to this host). For this
+reason, the default action is to log the incident, defer the address, and
+freeze the message. The following alternatives are provided for use in special
+cases:
+.numberpars $.
+\defer\
+.newline
+Delivery of the message is tried again later, but the message is not frozen.
+.nextp
+\reroute: <<domain>>\
+.newline
+The domain is changed to the given domain, and the address is passed back to
+be reprocessed by the routers. No rewriting of headers takes place. This
+behaviour is essentially a redirection.
+.nextp
+\reroute: rewrite: <<domain>>\
+.newline
+The domain is changed to the given domain, and the address is passed back to be
+reprocessed by the routers. Any headers that contain the original domain are
+rewritten.
+.nextp
+\pass\
+.newline
+The router passes the address to the next router, or to the router named in the
+\pass@_router\ option if it is set.
+.index \more\ option
+This overrides \no@_more\.
+
+During subsequent routing and delivery, the variable
+\$self@_hostname$\ contains the name of the local host that the router
+encountered. This can be used to distinguish between different cases for hosts
+with multiple names. The combination
+.display asis
+self = pass
+no_more
+.endd
+ensures that only those addresses that routed to the local host are passed on.
+Without \no@_more\, addresses that were declined for other reasons would also
+be passed to the next router.
+.nextp
+\fail\
+.newline
+Delivery fails and an error report is generated.
+.nextp
+\send\
+.newline
+.index local host||sending to
+The anomaly is ignored and the address is queued for the transport. This
+setting should be used with extreme caution. For an \%smtp%\ transport, it makes
+sense only in cases where the program that is listening on the SMTP port is not
+this version of Exim. That is, it must be some other MTA, or Exim with a
+different configuration file that handles the domain in another way.
+.endp
+
+.conf senders "address list$**$ (precondition)" unset
+.index router||checking senders
+If this option is set, the router is skipped unless the message's sender
+address matches something on the list.
+See section ~~SECTrouprecon for a list of the order in which preconditions
+are evaluated.
+
+There are issues concerning verification when the running of routers is
+dependent on the sender. When Exim is verifying the address in an \errors@_to\
+setting, it sets the sender to the null string. When using the \-bt-\ option to
+check a configuration file, it is necessary also to use the \-f-\ option to set
+an appropriate sender. For incoming mail, the sender is unset when verifying
+the sender, but is available when verifying any recipients. If the SMTP
+\\VRFY\\ command is enabled, it must be used after \\MAIL\\ if the sender
+address matters.
+
+.conf translate@_ip@_address string$**$ unset
+.index IP address||translating
+.index packet radio
+.index router||IP address translation
+There exist some rare networking situations (for example, packet radio) where
+it is helpful to be able to translate IP addresses generated by normal routing
+mechanisms into other IP addresses, thus performing a kind of manual IP
+routing. This should be done only if the normal IP routing of the TCP/IP stack
+is inadequate or broken. Because this is an extremely uncommon requirement, the
+code to support this option is not included in the Exim binary unless
+\\SUPPORT__TRANSLATE__IP__ADDRESS\\=yes is set in \(Local/Makefile)\.
+
+The \translate@_ip@_address\ string is expanded for every IP address generated
+by the router, with the generated address set in \$host@_address$\. If the
+expansion is forced to fail, no action is taken.
+For any other expansion error, delivery of the message is deferred.
+If the result of the expansion is an IP address, that replaces the original
+address; otherwise the result is assumed to be a host name -- this is looked up
+using \*gethostbyname()*\ (or \*getipnodebyname()*\ when available) to produce
+one or more replacement IP addresses. For example, to subvert all IP addresses
+in some specific networks, this could be added to a router:
+.display
+$smc{translate@_ip@_address = @\
+ @$@{lookup@{@$@{mask:@$host@_address/26@}@}lsearch@{/some/file@}@{@$value@}fail@}}
+.endd
+The file would contain lines like
+.display asis
+10.2.3.128/26 some.host
+10.8.4.34/26 10.44.8.15
+.endd
+You should not make use of this facility unless you really understand what you
+are doing.
+
+
+.conf transport string$**$ unset
+This option specifies the transport to be used when a router accepts an address
+and sets it up for delivery. A transport is never needed if a router is used
+only for verification. The value of the option is expanded at routing time,
+after the expansion of \errors@_to\,
+\headers@_add\, and \headers@_remove\,
+and result must be the name of one of the configured transports. If it is
+not, delivery is deferred.
+
+The \transport\ option is not used by the \%redirect%\ router, but it does have
+some private options that set up transports for pipe and file deliveries (see
+chapter ~~CHAPredirect).
+
+
+.conf transport@_current@_directory string$**$ unset
+.index current directory for local transport
+This option associates a current directory with any address that is routed
+to a local transport. This can happen either because a transport is
+explicitly configured for the router, or because it generates a delivery to a
+file or a pipe. During the delivery process (that is, at transport time), this
+option string is expanded and is set as the current directory, unless
+overridden by a setting on the transport.
+If the expansion fails for any reason, including forced failure, an error is
+logged, and delivery is deferred.
+See chapter ~~CHAPenvironment for details of the local delivery environment.
+
+
+
+.conf transport@_home@_directory string$**$ "see below"
+.index home directory||for local transport
+This option associates a home directory with any address that is routed to a
+local transport. This can happen either because a transport is explicitly
+configured for the router, or because it generates a delivery to a file or a
+pipe. During the delivery process (that is, at transport time), the option
+string is expanded and is set as the home directory, unless overridden by a
+setting of \home@_directory\ on the transport.
+If the expansion fails for any reason, including forced failure, an error is
+logged, and delivery is deferred.
+
+If the transport does not specify a home directory, and
+\transport@_home@_directory\ is not set for the router, the home directory for
+the tranport is taken from the password data if \check@_local@_user\ is set for
+the router. Otherwise it is taken from \router@_home@_directory\ if that option
+is set; if not, no home directory is set for the transport.
+
+See chapter ~~CHAPenvironment for further details of the local delivery
+environment.
+
+
+
+.conf unseen boolean$**$ false
+.index router||carrying on after success
+The result of string expansion for this option must be a valid boolean value,
+that is, one of the strings `yes', `no', `true', or `false'. Any other result
+causes an error, and delivery is deferred. If the expansion is forced to fail,
+the default value for the option (false) is used. Other failures cause delivery
+to be deferred.
+
+When this option is set true, routing does not cease if the router accepts the
+address. Instead, a copy of the incoming address is passed to the next router,
+overriding a false setting of \more\. There is little point in setting \more\
+false if \unseen\ is always true, but it may be useful in cases when the value
+of \unseen\ contains expansion items (and therefore, presumably, is sometimes
+true and sometimes false).
+
+The \unseen\ option can be used to cause
+.index copy of message (\unseen\ option)
+copies of messages to be delivered to some other destination, while also
+carrying out a normal delivery. In effect, the current address is made into a
+`parent' that has two children -- one that is delivered as specified by this
+router, and a clone that goes on to be routed further.
+
+Header lines added to the address (or specified for removal) by this router or
+by previous routers affect the `unseen' copy of the message only. The clone
+that continues to be processed by further routers starts with no added headers
+and none specified for removal.
+
+However, any data that was set by the \address@_data\ option in the current or
+previous routers is passed on. Setting this option has a similar effect to the
+\unseen\ command qualifier in filter files.
+
+
+.conf user string$**$ "see below"
+.index uid (user id)||local delivery
+.index local transports||uid and gid
+.index transport||local
+.index router||user for filter processing
+.index filter||user for processing
+When a router queues an address for a transport, and the transport does not
+specify a user, the user given here is used when running the delivery process.
+The user may be specified numerically or by name. If expansion fails, the
+error is logged and delivery is deferred.
+This user is also used by the \%redirect%\ router when running a filter file.
+The default is unset, except when \check@_local@_user\ is set. In this case,
+the default is taken from the password information. If the user is specified as
+a name, and \group\ is not set, the group associated with the user is used. See
+also \initgroups\ and \group\ and the discussion in chapter ~~CHAPenvironment.
+
+
+.conf verify "boolean (precondition)" true
+Setting this option has the effect of setting \verify@_sender\ and
+\verify@_recipient\ to the same value.
+
+.conf verify@_only "boolean (precondition)" false
+.index \\EXPN\\||with \verify@_only\
+.index \-bv-\ option
+.index router||used only when verifying
+If this option is set, the router is used only when verifying an address or
+testing with the \-bv-\ option, not when actually doing a delivery, testing
+with the \-bt-\ option, or running the SMTP \\EXPN\\ command. It can be further
+restricted to verifying only senders or recipients by means of \verify@_sender\
+and \verify@_recipient\.
+
+\**Warning**\: When the router is being run to verify addresses for an incoming
+SMTP message, Exim is not running as root, but under its own uid. If the router
+accesses any files, you need to make sure that they are accessible to the Exim
+user or group.
+
+.conf verify@_recipient "boolean (precondition)" true
+If this option is false, the router is skipped when verifying recipient
+addresses
+or testing recipient verification using \-bv-\.
+See section ~~SECTrouprecon for a list of the order in which preconditions
+are evaluated.
+
+.conf verify@_sender "boolean (precondition)" true
+If this option is false, the router is skipped when verifying sender addresses
+or testing sender verification using \-bvs-\.
+See section ~~SECTrouprecon for a list of the order in which preconditions
+are evaluated.
+
+.endconf
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The accept router
+.set runningfoot "accept router"
+.index \%accept%\ router
+.index routers||\%accept%\
+The \%accept%\ router has no private options of its own. Unless it is being used
+purely for verification (see \verify@_only\) a transport is required to be
+defined by the generic \transport\ option. If the preconditions that are
+specified by generic options are met, the router accepts the address and queues
+it for the given transport. The most common use of this router is for setting
+up deliveries to local mailboxes. For example:
+.display asis
+localusers:
+ driver = accept
+ domains = mydomain.example
+ check_local_user
+ transport = local_delivery
+.endd
+The \domains\ condition in this example checks the domain of the address, and
+\check@_local@_user\ checks that the local part is the login of a local user.
+When both preconditions are met, the \%accept%\ router runs, and queues the
+address for the \%local@_delivery%\ transport.
+
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The dnslookup router
+.rset CHAPdnslookup "~~chapter"
+.set runningfoot "dnslookup router"
+.index \%dnslookup%\ router
+.index routers||\%dnslookup%\
+The \%dnslookup%\ router looks up the hosts that handle mail for the given
+domain in the DNS. A transport must always be set for this router, unless
+\verify@_only\ is set.
+
+.em
+If SRV support is configured (see \check@_srv\ below), Exim first searches for
+SRV records. If none are found, or if SRV support is not configured,
+MX records are looked up. If no MX records exist, address records are sought.
+However, \mx@_domains\ can be set to disable the direct use of address records.
+
+MX records of equal priority are sorted by Exim into a random order. Exim then
+looks for address records for the host names obtained from MX or SRV records.
+When a host has more than one IP address, they are sorted into a random order,
+except that IPv6 addresses are always sorted before IPv4 addresses. If all the
+IP addresses found are discarded by a setting of the \ignore@_target@_hosts\
+generic option, the router declines.
+
+Unless they have the highest priority (lowest MX value), MX records that point
+to the local host, or to any host name that matches \hosts__treat__as__local\,
+are discarded, together with any other MX records of equal or lower priority.
+.nem
+
+.index MX record||pointing to local host
+.index local host||MX pointing to
+.index \self\ option||in \%dnslookup%\ router
+If the host pointed to by the highest priority MX record, or looked up as an
+address record, is the local host, or matches \hosts__treat__as__local\, what
+happens is controlled by the generic \self\ option.
+
+There are a number of private options that can be used to vary the way the DNS
+lookup is handled.
+
+
+.startconf
+.index options||\%dnslookup%\ router
+.conf check@_secondary@_mx boolean false
+.index MX record||checking for secondary
+If this option is set, the router declines unless the local host is found in
+(and removed from) the list of hosts obtained by MX lookup. This can be used to
+process domains for which the local host is a secondary mail exchanger
+differently to other domains. The way in which Exim decides whether a host is
+the local host is described in section ~~SECTreclocipadd.
+
+.em
+.conf check@_srv string$**$ unset
+.index SRV record||enabling use of
+The dnslookup router supports the use of SRV records (see RFC 2782) in
+addition to MX and address records. The support is disabled by default. To
+enable SRV support, set the \check@_srv\ option to the name of the service
+required. For example,
+.display asis
+check_srv = smtp
+.endd
+looks for SRV records that refer to the normal smtp service. The option is
+expanded, so the service name can vary from message to message or address
+to address. This might be helpful if SRV records are being used for a
+submission service. If the expansion is forced to fail, the \check@_srv\
+option is ignored, and the router proceeds to look for MX records in the
+normal way.
+
+When the expansion succeeds, the router searches first for SRV records for
+the given service (it assumes TCP protocol). A single SRV record with the
+host name \"."\ indicates `no such service for this domain'; if this is
+encountered, the router declines. If other kinds of SRV record are found,
+they are used to construct a host list for delivery according to the rules
+of RFC 2782. MX records are not sought in this case.
+
+However, when no SRV records are found, MX records (and address records)
+are sought in the traditional way. In other words, SRV records take
+precedence over MX records, just as MX records take precedence over address
+records. Note that this behaviour is not sanctioned by RFC 2782, though a
+previous draft RFC defined it. It is apparently believed that MX records
+are sufficient for email and that SRV records should not be used for this
+purpose. However, SRV records have an additional `weight' feature which
+some people might find useful when trying to split an SMTP load between
+hosts of different power.
+.nem
+
+.conf mx@_domains "domain list$**$" unset
+.index MX record||required to exist
+.index SRV record||required to exist
+.em
+A domain that matches \mx@_domains\ is required to have either an MX or an SRV
+record in order to be recognised. (The name of this option could be improved.)
+.nem
+For example, if all the mail hosts in \*fict.example*\ are known to have MX
+records, except for those in \*discworld.fict.example*\, you could use this
+setting:
+.display asis
+mx_domains = ! *.discworld.fict.example : *.fict.example
+.endd
+This specifies that messages addressed to a domain that matches the list but
+has no MX record should be bounced immediately instead of being routed using
+the address record.
+
+.conf qualify@_single boolean true
+.index DNS||resolver options
+.index DNS||qualifying single-component names
+When this option is true, the resolver option \\RES@_DEFNAMES\\ is set for DNS
+lookups. Typically, but not standardly, this causes the resolver to qualify
+single-component names with the default domain. For example, on a machine
+called \*dictionary.ref.example*\, the domain \*thesaurus*\ would be changed to
+\*thesaurus.ref.example*\ inside the resolver. For details of what your resolver
+actually does, consult your man pages for \*resolver*\ and \*resolv.conf*\.
+
+
+.conf rewrite@_headers boolean true
+.index rewriting||header lines
+.index header lines||rewriting
+If the domain name in the address that is being processed is not fully
+qualified, it may be expanded to its full form by a DNS lookup. For example, if
+an address is specified as \*dormouse@@teaparty*\, the domain might be
+expanded to \*teaparty.wonderland.fict.example*\. Domain expansion can also
+occur as a result of setting the \widen@_domains\ option. If \rewrite@_headers\
+is true, all occurrences of the abbreviated domain name in any ::Bcc::, ::Cc::,
+::From::, ::Reply-to::, ::Sender::, and ::To:: header lines of the message are
+rewritten with the full domain name.
+
+This option should be turned off only when it is known that no message is
+ever going to be sent outside an environment where the abbreviation makes
+sense.
+
+When an MX record is looked up in the DNS and matches a wildcard record, name
+servers normally return a record containing the name that has been looked up,
+making it impossible to detect whether a wildcard was present or not. However,
+some name servers have recently been seen to return the wildcard entry. If the
+name returned by a DNS lookup begins with an asterisk, it is not used for
+header rewriting.
+
+.conf same@_domain@_copy@_routing boolean false
+.index address||copying routing
+Addresses with the same domain are normally routed by the \%dnslookup%\ router
+to the same list of hosts. However, this cannot be presumed, because the router
+options and preconditions may refer to the local part of the address. By
+default, therefore, Exim routes each address in a message independently. DNS
+servers run caches, so repeated DNS lookups are not normally expensive, and in
+any case, personal messages rarely have more than a few recipients.
+
+If you are running mailing lists with large numbers of subscribers at the same
+domain, and you are using a \%dnslookup%\ router which is independent of the
+local part, you can set \same__domain__copy@_routing\ to bypass repeated DNS
+lookups for identical domains in one message. In this case, when \%dnslookup%\
+routes an address to a remote transport, any other unrouted addresses in the
+message that have the same domain are automatically given the same routing
+without processing them independently,
+provided the following conditions are met:
+.numberpars $.
+No router that processed the address specified \headers@_add\ or
+\headers@_remove\.
+.nextp
+The router did not change the address in any way, for example, by `widening'
+the domain.
+.endp
+
+
+.conf search@_parents boolean false
+.index DNS||resolver options
+When this option is true, the resolver option \\RES@_DNSRCH\\ is set for DNS
+lookups. This is different from the \qualify@_single\ option in that it applies
+to domains containing dots. Typically, but not standardly, it causes the
+resolver to search for the name in the current domain and in parent domains.
+For example, on a machine in the \*fict.example*\ domain, if looking up
+\*teaparty.wonderland*\ failed, the resolver would try
+\*teaparty.wonderland.fict.example*\. For details of what your resolver
+actually does, consult your man pages for \*resolver*\ and \*resolv.conf*\.
+
+Setting this option true can cause problems in domains that have a wildcard MX
+record, because any domain that does not have its own MX record matches the
+local wildcard.
+
+.conf widen@_domains "string list" unset
+.index domain||partial, widening
+If a DNS lookup fails and this option is set, each of its strings in turn is
+added onto the end of the domain, and the lookup is tried again. For example,
+if
+.display asis
+widen_domains = fict.example:ref.example
+.endd
+is set and a lookup of \*klingon.dictionary*\ fails,
+\*klingon.dictionary.fict.example*\ is looked up, and if this fails,
+\*klingon.dictionary.ref.example*\ is tried. Note that the \qualify@_single\
+and \search@_parents\ options can cause some widening to be undertaken inside
+the DNS resolver.
+
+.endconf
+
+.em
+.section Effect of qualify@_single and search@_parents
+When a domain from an envelope recipient is changed by the resolver as a result
+of the \qualify@_single\ or \search@_parents\ options, Exim rewrites the
+corresponding address in the message's header lines unless \rewrite@_headers\
+is set false. Exim then re-routes the address, using the full domain.
+
+These two options affect only the DNS lookup that takes place inside the router
+for the domain of the address that is being routed. They do not affect lookups
+such as that implied by
+.display asis
+domains = @mx_any
+.endd
+that may happen while processing a router precondition before the router is
+entered. No widening ever takes place for these lookups.
+.nem
+
+
+
+
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The ipliteral router
+.set runningfoot "ipliteral router"
+.index \%ipliteral%\ router
+.index domain literal||routing
+.index routers||\%ipliteral%\
+This router has no private options. Unless it is being used purely for
+verification (see \verify@_only\) a transport is required to be defined by the
+generic \transport\ option. The router accepts the address if its domain part
+takes the form of an RFC 2822 domain literal, that is, an IP address enclosed
+in square brackets. For example, this router handles the address
+.display asis
+root@[192.168.1.1]
+.endd
+by setting up delivery to the host with that IP address.
+
+.em
+If the IP address matches something in \ignore@_target@_hosts\, the router
+declines.
+.nem
+.index \self\ option||in \%ipliteral%\ router
+If an IP literal turns out to refer to the local host, the generic \self\
+option determines what happens.
+
+The RFCs require support for domain literals; however, their use is
+controversial in today's Internet. If you want to use this router, you must
+also set the main configuration option \allow@_domain@_literals\. Otherwise,
+Exim will not recognize the domain literal syntax in addresses.
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The iplookup router
+.set runningfoot "iplookup router"
+.index \%iplookup%\ router
+.index routers||\%iplookup%\
+The \%iplookup%\ router was written to fulfil a specific requirement in
+Cambridge University. For this reason, it is not included in the binary of Exim
+by default. If you want to include it, you must set
+.display asis
+ROUTER_IPLOOKUP=yes
+.endd
+in your \(Local/Makefile)\ configuration file.
+
+The \%iplookup%\ router routes an address by sending it over a TCP or UDP
+connection to one or more specific hosts. The host can then return the same or
+a different address -- in effect rewriting the recipient address in the
+message's envelope. The new address is then passed on to subsequent routers.
+
+
+If this process fails, the address can be passed on to
+other routers, or delivery can be deferred.
+
+Background, for those that are interested: We have an Oracle database of all
+Cambridge users, and one of the items of data it maintains for each user is
+where to send mail addressed to \*user@@cam.ac.uk*\. The MX records for
+\*cam.ac.uk*\ point to a central machine that has a large alias list that is
+abstracted from the database. Mail from outside is switched by this system, and
+originally internal mail was also done this way. However, this resulted in a
+fair number of messages travelling from some of our larger systems to the
+switch and back again. The Oracle machine now runs a UDP service that can be
+called by the \%iplookup%\ router in Exim to find out where \*user@@cam.ac.uk*\
+addresses really have to go; this saves passing through the central switch, and
+in many cases saves doing any remote delivery at all.
+
+Since \%iplookup%\ is just a rewriting router, a transport must not be
+specified for it.
+
+.startconf
+.index options||\%iplookup%\ router
+
+.conf hosts string unset
+This option must be supplied. Its value is a colon-separated list of host
+names. The hosts are looked up using \*gethostbyname()*\
+(or \*getipnodebyname()*\ when available)
+and are tried in order until one responds to the query. If none respond, what
+happens is controlled by \optional\.
+
+.conf optional boolean false
+If \optional\ is true, if no response is obtained from any host, the address is
+passed to the next router, overriding \no@_more\. If \optional\ is false,
+delivery to the address is deferred.
+
+.conf port integer 0
+.index port||\%iplookup%\ router
+This option must be supplied. It specifies the port number for the TCP or UDP
+call.
+
+.conf protocol string "udp"
+This option can be set to `udp' or `tcp' to specify which of the two protocols
+is to be used.
+
+.conf query string$**$ "$tt{@$local@_part@@@$domain @$local@_part@@@$domain}"
+This defines the content of the query that is sent to the remote hosts. The
+repetition serves as a way of checking that a response is to the correct query
+in the default case (see \response@_pattern\ below).
+
+.conf reroute string$**$ unset
+If this option is not set, the rerouted address is precisely the byte string
+returned by the remote host, up to the first white space, if any. If set, the
+string is expanded to form the rerouted address. It can include parts matched
+in the response by \response@_pattern\ by means of numeric variables such as
+\$1$\, \$2$\, etc. The variable \$0$\ refers to the entire input string,
+whether or not a pattern is in use. In all cases, the rerouted address must end
+up in the form \*local@_part@@domain*\.
+
+.conf response@_pattern string unset
+This option can be set to a regular expression that is applied to the string
+returned from the remote host. If the pattern does not match the response, the
+router declines. If \response@_pattern\ is not set, no checking of the response
+is done, unless the query was defaulted, in which case there is a check that
+the text returned after the first white space is the original address. This
+checks that the answer that has been received is in response to the correct
+question. For example, if the response is just a new domain, the following
+could be used:
+.display asis
+response_pattern = ^([^@]+)$
+reroute = $local_part@$1
+.endd
+
+.conf timeout time 5s
+This specifies the amount of time to wait for a response from the remote
+machine. The same timeout is used for the \*connect()*\ function for a TCP
+call. It does not apply to UDP.
+
+.endconf
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The manualroute router
+.set runningfoot "manualroute router"
+.index \%manualroute%\ router
+.index routers||\%manualroute%\
+.index domain||manually routing
+The \%manualroute%\ router is so-called because it provides a way of manually
+routing an address according to its domain. It is mainly used when you want to
+route addresses to remote hosts according to your own rules, bypassing the
+normal DNS routing that looks up MX records. However, \%manualroute%\ can also
+route to local transports, a facility that may be useful if you want to save
+messages for dial-in hosts in local files.
+
+The \%manualroute%\ router compares a list of domain patterns with the domain it
+is trying to route. If there is no match, the router declines. Each pattern has
+associated with it a list of hosts and some other optional data, which may
+include a transport. The combination of a pattern and its data is called a
+`routing rule'. For patterns that do not have an associated transport, the
+generic \transport\ option must specify a transport, unless the router is being
+used purely for verification (see \verify@_only\).
+
+In the case of verification, matching the domain pattern is sufficient for the
+router to accept the address. When actually routing an address for delivery,
+an address that matches a domain pattern is queued for the associated
+transport. If the transport is not a local one, a host list must be associated
+with the pattern; IP addresses are looked up for the hosts, and these are
+passed to the transport along with the mail address. For local transports, a
+host list is optional. If it is present, it is passed in \$host$\ as a single
+text string.
+
+The list of routing rules can be provided as an inline string in \route@_list\,
+or the data can be obtained by looking up the domain in a file or database by
+setting \route@_data\. Only one of these settings may appear in any one
+instance of \%manualroute%\. The format of routing rules is described below,
+following the list of private options.
+
+.section Private options for manualroute
+.rset SECTprioptman "~~chapter.~~section"
+
+The private options for the \%manualroute%\ router are as follows:
+
+.startconf
+.index options||\%manualroute%\ router
+
+.conf host@_find@_failed string "freeze"
+This option controls what happens when \%manualroute%\ tries to find an IP
+address for a host, and the host does not exist. The option can be set to one
+of
+.display asis
+decline
+defer
+fail
+freeze
+pass
+.endd
+The default assumes that this state is a serious configuration error. The
+difference between `pass' and `decline' is that the former forces the address
+to be passed to the next router (or the router defined by \pass@_router\),
+.index \more\ option
+overriding \no@_more\, whereas the latter passes the address to the next router
+only if \more\ is true.
+
+This option applies only to a definite `does not exist' state; if a host lookup
+gets a temporary error, delivery is deferred unless the generic
+\pass@_on@_timeout\ option is set.
+
+.conf hosts@_randomize boolean false
+.index randomized host list
+.index host||list of, randomized
+If this option is set, the order of the items in a host list in a routing rule
+is randomized each time the list is used, unless an option in the routing rule
+overrides (see below). Randomizing the order of a host list can be used to do
+crude load sharing. However, if more than one mail address is routed by the
+same router to the same host list, the host lists are considered to be the same
+(even though they may be randomized into different orders) for the purpose of
+deciding whether to batch the deliveries into a single SMTP transaction.
+
+When \hosts@_randomize\ is true, a host list may be split
+into groups whose order is separately randomized. This makes it possible to
+set up MX-like behaviour. The boundaries between groups are indicated by an
+item that is just \"+"\ in the host list. For example:
+.display asis
+route_list = * host1:host2:host3:+:host4:host5
+.endd
+The order of the first three hosts and the order of the last two hosts is
+randomized for each use, but the first three always end up before the last two.
+If \hosts@_randomize\ is not set, a \"+"\ item in the list is ignored. If a
+randomized host list is passed to an \%smtp%\ transport that also has
+\hosts@_randomize set\, the list is not re-randomized.
+
+.conf route@_data string$**$ unset
+If this option is set, it must expand to yield the data part of a routing rule.
+Typically, the expansion string includes a lookup based on the domain. For
+example:
+.display asis
+route_data = ${lookup{$domain}dbm{/etc/routes}}
+.endd
+If the expansion is forced to fail, or the result is an empty string, the
+router declines. Other kinds of expansion failure cause delivery to be
+deferred.
+
+.conf route@_list "string list, semicolon-separated" unset
+This string is a list of routing rules, in the form defined below. Note that,
+unlike most string lists, the items are separated by semicolons. This is so
+that they may contain colon-separated host lists.
+
+.conf same@_domain@_copy@_routing boolean false
+.index address||copying routing
+Addresses with the same domain are normally routed by the \%manualroute%\ router
+to the same list of hosts. However, this cannot be presumed, because the router
+options and preconditions may refer to the local part of the address. By
+default, therefore, Exim routes each address in a message independently. DNS
+servers run caches, so repeated DNS lookups are not normally expensive, and in
+any case, personal messages rarely have more than a few recipients.
+
+If you are running mailing lists with large numbers of subscribers at the same
+domain, and you are using a \%manualroute%\ router which is independent of the
+local part, you can set \same@_domain@_copy@_routing\ to bypass repeated DNS
+lookups for identical domains in one message. In this case, when \%manualroute%\
+routes an address to a remote transport, any other unrouted addresses in the
+message that have the same domain are automatically given the same routing
+without processing them independently. However, this is only done if
+\headers@_add\ and \headers@_remove\ are unset.
+
+.endconf
+
+
+.section Routing rules in route@_list
+The value of \route@_list\ is a string consisting of a sequence of routing
+rules, separated by semicolons. If a semicolon is needed in a rule, it can be
+entered as two semicolons. Empty rules are ignored. The format of each rule is
+.display
+<<domain pattern>> <<list of hosts>> <<options>>
+.endd
+The following example contains two rules, each with a simple domain pattern and
+no options:
+.display asis
+route_list = \
+ dict.ref.example mail-1.ref.example:mail-2.ref.example ; \
+ thes.ref.example mail-3.ref.example:mail-4.ref.example
+.endd
+The three parts of a rule are separated by white space. The pattern and the
+list of hosts can be enclosed in quotes if necessary, and if they are, the
+usual quoting rules apply. Each rule in a \route@_list\ must start with a
+single domain pattern, which is the only mandatory item in the rule. The
+pattern is in the same format as one item in a domain list (see section
+~~SECTdomainlist),
+except that it may not be the name of an interpolated file.
+That is, it may be wildcarded, or a regular expression, or a file or database
+lookup (with semicolons doubled, because of the use of semicolon as a separator
+in a \route@_list\).
+
+The rules in \route@_list\ are searched in order until one of the patterns
+matches the domain that is being routed. The list of hosts and then options are
+then used as described below. If there is no match, the router declines. When
+\route@_list\ is set, \route@_data\ must not be set.
+
+
+.section Routing rules in route@_data
+The use of \route@_list\ is convenient when there are only a small number of
+routing rules. For larger numbers, it is easier to use a file or database to
+hold the routing information, and use the \route@_data\ option instead.
+The value of \route@_data\ is a list of hosts, followed by (optional) options.
+Most commonly, \route@_data\ is set as a string that contains an
+expansion lookup. For example, suppose we place two routing rules in a file
+like this:
+.display asis
+dict.ref.example: mail-1.ref.example:mail-2.ref.example
+thes.ref.example: mail-3.ref.example:mail-4.ref.example
+.endd
+This data can be accessed by setting
+.display asis
+route_data = ${lookup{$domain}lsearch{/the/file/name}}
+.endd
+Failure of the lookup results in an empty string, causing the router to
+decline. However, you do not have to use a lookup in \route@_data\. The only
+requirement is that the result of expanding the string is a list of hosts,
+possibly followed by options, separated by white space. The list of hosts must
+be enclosed in quotes if it contains white space.
+
+
+
+.section Format of the list of hosts
+A list of hosts, whether obtained via \route@_data\ or \route@_list\, is always
+separately expanded before use. If the expansion fails, the router declines.
+The result of the expansion must be a colon-separated list of names and/or
+IP addresses. IP addresses are not enclosed in brackets.
+
+If the list of hosts was obtained from a \route@_list\ item, the following
+variables are set during its expansion:
+.index numerical variables (\$1$\, \$2$\, etc)||in \%manualroute%\ router
+.numberpars $.
+If the domain was matched against a regular expression, the numeric variables
+\$1$\, \$2$\, etc. may be set.
+.nextp
+\$0$\ is always set to the entire domain.
+.nextp
+\$1$\ is also set when partial matching is done in a file lookup.
+.nextp
+.index \$value$\
+If the pattern that matched the domain was a lookup item, the data that was
+looked up is available in the expansion variable \$value$\.
+.endp
+
+
+.em
+.section How the list of hosts is used
+When an address is routed to an \%smtp%\ transport by \%manualroute%\, each of
+the hosts is tried, in the order specified, when carrying out the SMTP
+delivery. However, the order can be changed by setting the \hosts@_randomize\
+option, either on the router (see section ~~SECTprioptman above), or on the
+transport.
+
+Hosts may be listed by name or by IP address. An unadorned name in the list of
+hosts is interpreted as a host name. A name that is followed by \"/MX"\ is
+interpreted as an indirection to a sublist of hosts obtained by looking up MX
+records in the DNS. For example:
+.display asis
+route_list = * x.y.z:p.q.r/MX:e.f.g
+.endd
+If the \hosts@_randomize\ option is set, the order of the items in the list is
+randomized before any lookups are done. Exim then scans the list; for any name
+that is not followed by \"/MX"\ it looks up an IP address. If this turns out to
+be an interface on the local host and the item is not the first in the list,
+Exim discards it and any subsequent items. If it is the first item, what
+happens is controlled by the
+.index \self\ option||in \%manualroute%\ router
+\self\ option of the router.
+
+A name on the list that is followed by \"/MX"\ is replaced with the list of
+hosts obtained by looking up MX records for the name. This is always a DNS
+lookup; the \bydns\ and \byname\ options (see section ~~SECThowoptused below)
+are not relevant here. The order of these hosts is determined by the preference
+values in the MX records, according to the usual rules. Because randomizing
+happens before the MX lookup, it does not affect the order that is defined by
+MX preferences.
+.nem
+
+If the local host is present in the sublist obtained from MX records, but is
+not the most preferred host in that list, it and any equally or less
+preferred hosts are removed before the sublist is inserted into the main list.
+
+If the local host is the most preferred host in the MX list, what happens
+depends on where in the original list of hosts the \"/MX"\ item appears. If it
+is not the first item (that is, there are previous hosts in the main list),
+Exim discards this name and any subsequent items in the main list.
+
+If the MX item is first in the list of hosts, and the local host is the
+most preferred host, what happens is controlled by the \self\ option of the
+router.
+
+DNS failures when lookup up the MX records are treated in the same way as DNS
+failures when looking up IP addresses: \pass@_on@_timeout\ and
+\host@_find@_failed\ are used when relevant.
+
+.em
+The generic \ignore@_target@_hosts\ option applies to all hosts in the list,
+whether obtained from an MX lookup or not.
+.nem
+
+
+.section How the options are used
+.rset SECThowoptused "~~chapter.~~section"
+The options are a sequence of words; in practice no more than three are ever
+present. One of the words can be the name of a transport; this overrides the
+\transport\ option on the router for this particular routing rule only. The
+other words (if present) control randomization of the list of hosts on a
+per-rule basis, and how the IP addresses of the hosts are to be found when
+routing to a remote transport. These options are as follows:
+.numberpars $.
+\randomize\: randomize the order of the hosts in this list, overriding the
+setting of \hosts@_randomize\ for this routing rule only.
+.nextp
+\no@_randomize\: do not randomize the order of the hosts in this list,
+overriding the setting of \hosts@_randomize\ for this routing rule only.
+.nextp
+\byname\: use \*getipnodebyname()*\ (\*gethostbyname()*\ on older systems) to
+find IP addresses. This function may ultimately cause a DNS lookup, but it may
+also look in \(/etc/hosts)\ or other sources of information.
+.nextp
+\bydns\: look up address records for the hosts directly in the DNS; fail if
+no address records are found. If there is a temporary DNS error (such as a
+timeout), delivery is deferred.
+.endp
+For example:
+.display asis
+route_list = domain1 host1:host2:host3 randomize bydns;\
+ domain2 host4:host5
+.endd
+If neither \byname\ nor \bydns\ is given, Exim behaves as follows: First, a DNS
+lookup is done. If this yields anything other than \\HOST@_NOT@_FOUND\\, that
+result is used. Otherwise, Exim goes on to try a call to \*getipnodebyname()*\
+or \*gethostbyname()*\, and the result of the lookup is the result of that
+call.
+
+\**Warning**\: It has been discovered that on some systems, if a DNS lookup
+called via \*getipnodebyname()*\ times out, \\HOST@_NOT@_FOUND\\ is returned
+instead of \\TRY@_AGAIN\\. That is why the default action is to try a DNS
+lookup first. Only if that gives a definite `no such host' is the local
+function called.
+
+
+
+If no IP address for a host can be found, what happens is controlled by the
+\host@_find@_failed\ option.
+
+When an address is routed to a local transport, IP addresses are not looked up.
+The host list is passed to the transport in the \$host$\ variable.
+
+
+.section Manualroute examples
+In some of the examples that follow, the presence of the \remote@_smtp\
+transport, as defined in the default configuration file, is assumed:
+
+.numberpars $.
+.index smart host||example router
+The \%manualroute%\ router can be used to forward all external mail to a
+\*smart host*\. If you have set up, in the main part of the configuration, a
+named domain list that contains your local domains, for example,
+.display asis
+domainlist local_domains = my.domain.example
+.endd
+you can arrange for all other domains to be routed to a smart host by making
+your first router something like this:
+.display asis
+smart_route:
+ driver = manualroute
+ domains = !+local_domains
+ transport = remote_smtp
+ route_list = * smarthost.ref.example
+.endd
+This causes all non-local addresses to be sent to the single host
+\*smarthost.ref.example*\. If a colon-separated list of smart hosts is given,
+they are tried in order
+(but you can use \hosts@_randomize\ to vary the order each time).
+Another way of configuring the same thing is this:
+.display asis
+smart_route:
+ driver = manualroute
+ transport = remote_smtp
+ route_list = !+local_domains smarthost.ref.example
+.endd
+There is no difference in behaviour between these two routers as they stand.
+However, they behave differently if \no@_more\ is added to them. In the first
+example, the router is skipped if the domain does not match the \domains\
+precondition; the following router is always tried. If the router runs, it
+always matches the domain and so can never decline. Therefore, \no@_more\ would
+have no effect. In the second case, the router is never skipped; it always
+runs. However, if it doesn't match the domain, it declines. In this case
+\no@_more\ would prevent subsequent routers from running.
+
+.nextp
+.index mail hub example
+A \*mail hub*\ is a host which receives mail for a number of domains via MX
+records in the DNS and delivers it via its own private routing mechanism. Often
+the final destinations are behind a firewall, with the mail hub being the one
+machine that can connect to machines both inside and outside the firewall. The
+\%manualroute%\ router is usually used on a mail hub to route incoming messages
+to the correct hosts. For a small number of domains, the routing can be inline,
+using the \route@_list\ option, but for a larger number a file or database
+lookup is easier to manage.
+
+If the domain names are in fact the names of the machines to which the mail is
+to be sent by the mail hub, the configuration can be quite simple. For
+example,
+.display asis
+hub_route:
+ driver = manualroute
+ transport = remote_smtp
+ route_list = *.rhodes.tvs.example $domain
+.endd
+This configuration routes domains that match \"*.rhodes.tvs.example"\ to hosts
+whose names are the same as the mail domains. A similar approach can be taken
+if the host name can be obtained from the domain name by a string manipulation
+that the expansion facilities can handle. Otherwise, a lookup based on the
+domain can be used to find the host:
+.display asis
+through_firewall:
+ driver = manualroute
+ transport = remote_smtp
+ route_data = ${lookup {$domain} cdb {/internal/host/routes}}
+.endd
+The result of the lookup must be the name or IP address of the host (or
+hosts) to which the address is to be routed. If the lookup fails, the route
+data is empty, causing the router to decline. The address then passes to the
+next router.
+
+.nextp
+.index batched SMTP output example
+.index SMTP||batched outgoing, example
+You can use \%manualroute%\ to deliver messages to pipes or files in batched
+SMTP format for onward transportation by some other means. This is one way of
+storing mail for a dial-up host when it is not connected. The route list entry
+can be as simple as a single domain name in a configuration like this:
+.display asis
+save_in_file:
+ driver = manualroute
+ transport = batchsmtp_appendfile
+ route_list = saved.domain.example
+.endd
+though often a pattern is used to pick up more than one domain. If there are
+several domains or groups of domains with different transport requirements,
+different transports can be listed in the routing information:
+.display asis
+save_in_file:
+ driver = manualroute
+ route_list = \
+ *.saved.domain1.example $domain batch_appendfile; \
+ *.saved.domain2.example \
+ ${lookup{$domain}dbm{/domain2/hosts}{$value}fail} \
+ batch_pipe
+.endd
+The first of these just passes the domain in the \$host$\ variable, which
+doesn't achieve much (since it is also in \$domain$\), but the second does a
+file lookup to find a value to pass, causing the router to decline to handle
+the address if the lookup fails.
+.nextp
+.index UUCP||example of router for
+Routing mail directly to UUCP software is a specific case of the use of
+\%manualroute%\ in a gateway to another mail environment. This is an example of
+one way it can be done:
+.display asis
+# Transport
+uucp:
+ driver = pipe
+ user = nobody
+ command = /usr/local/bin/uux -r - \
+ ${substr_-5:$host}!rmail ${local_part}
+ return_fail_output = true
+.endd
+.display asis
+# Router
+uucphost:
+ transport = uucp
+ driver = manualroute
+ route_data = \
+ ${lookup{$domain}lsearch{/usr/local/exim/uucphosts}}
+.endd
+The file \(/usr/local/exim/uucphosts)\ contains entries like
+.display asis
+darksite.ethereal.example: darksite.UUCP
+.endd
+It can be set up more simply without adding and removing `.UUCP' but this way
+makes clear the distinction between the domain name
+\*darksite.ethereal.example*\ and the UUCP host name \*darksite*\.
+.endp
+
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The queryprogram router
+.set runningfoot "queryprogram router"
+.rset CHAPdriverlast "~~chapter"
+.index \%queryprogram%\ router
+.index routers||\%queryprogram%\
+.index routing||by external program
+The \%queryprogram%\ router routes an address by running an external command and
+acting on its output. This is an expensive way to route, and is intended mainly
+for use in lightly-loaded systems, or for performing experiments. However, if
+it is possible to use the precondition options (\domains\, \local@_parts\,
+etc) to skip this router for most addresses, it could sensibly be used in
+special cases, even on a busy host. There are the following private options:
+
+.startconf
+.index options||\%queryprogram%\ router
+.conf command string$**$ unset
+This option must be set. It specifies the command that is to be run. The
+command is split up into a command name and arguments, and then each is
+expanded separately (exactly as for a \%pipe%\ transport, described in chapter
+~~CHAPpipetransport).
+
+.conf command@_group string unset
+.index gid (group id)||in \%queryprogram%\ router
+This option specifies a gid to be set when running the command. It must be set
+if \command@_user\ specifies a numerical uid. If it begins with a digit, it is
+interpreted as the numerical value of the gid. Otherwise it is looked up using
+\*getgrnam()*\.
+
+.conf command@_user string unset
+.index uid (user id)||for \%queryprogram%\
+This option must be set. It specifies the uid which is set when running the
+command. If it begins with a digit it is interpreted as the numerical value of
+the uid. Otherwise, it is looked up using \*getpwnam()*\ to obtain a value for
+the uid and, if \command@_group\ is not set, a value for the gid also.
+
+.conf current@_directory string /
+This option specifies an absolute path which is made the current directory
+before running the command.
+
+.conf timeout time 1h
+If the command does not complete within the timeout period, its process group
+is killed and the message is frozen. A value of zero time specifies no
+timeout.
+
+.endconf
+
+The standard output of the command is connected to a pipe, which is read when
+the command terminates. It should consist of a single line of output,
+containing up to five fields, separated by white space. The first field is one
+of the following words (case-insensitive):
+.numberpars $.
+\*Accept*\: routing succeeded; the remaining fields specify what to do (see
+below).
+.nextp
+\*Decline*\: the router declines; pass the address to the next router, unless
+\no@_more\ is set.
+.nextp
+\*Fail*\: routing failed; do not pass the address to any more routers. Any
+subsequent text on the line is an error message. If the router is run as part
+of address verification during an incoming SMTP message, the message is
+included in the SMTP response.
+.nextp
+\*Defer*\: routing could not be completed at this time; try again later. Any
+subsequent text on the line is an error message which is logged. It is not
+included in any SMTP response.
+.nextp
+\*Freeze*\: the same as \*defer*\, except that the message is frozen.
+.nextp
+\*Pass*\: pass the address to the next router (or the router specified by
+\pass@_router\), overriding \no@_more\.
+.nextp
+\*Redirect*\: the message is redirected. The remainder of the line is a list of
+new addresses, which are routed independently, starting with the first router,
+or the router specified by \redirect@_router\, if set.
+.endp
+When the first word is \*accept*\, the remainder of the line consists of a
+number of keyed data values, as follows (split into two lines here, to fit on
+the page):
+.display
+ACCEPT TRANSPORT=<<transport>> HOSTS=<<list of hosts>>
+ LOOKUP=byname|bydns DATA=<<text>>
+.endd
+The data items can be given in any order, and all are optional. If no transport
+is included, the transport specified by the generic \transport\ option is used.
+The list of hosts and the lookup type are needed only if the transport is an
+\%smtp%\ transport that does not itself supply a list of hosts.
+
+The format of the list of hosts is the same as for the \%manualroute%\ router.
+As well as host names and IP addresses, it may contain names followed by
+\"/MX"\ to specify sublists of hosts that are obtained by looking up MX
+records.
+
+If the lookup type is not specified, Exim behaves as follows when trying to
+find an IP address for each host: First, a DNS lookup is done. If this yields
+anything other than \\HOST@_NOT@_FOUND\\, that result is used. Otherwise, Exim
+goes on to try a call to \*getipnodebyname()*\ or \*gethostbyname()*\, and the
+result of the lookup is the result of that call.
+
+If the DATA field is set, its value is placed in the \$address@_data$\
+variable. For example, this return line
+.display asis
+accept hosts=x1.y.example:x2.y.example data="rule1"
+.endd
+routes the address to the default transport, with a host list containing two
+hosts. When the transport runs, the string `rule1' is in \$address@_data$\.
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The redirect router
+.set runningfoot "redirect router"
+.rset CHAPredirect "~~chapter"
+.index \%redirect%\ router
+.index routers||\%redirect%\
+.index alias file||in a \%redirect%\ router
+.index address redirection||\%redirect%\ router
+The \%redirect%\ router handles several kinds of address redirection. Its most
+common uses are for resolving local part aliases from a central alias file
+(usually called \(/etc/aliases)\) and for handling users' personal \(.forward)\
+files, but it has many other potential uses. The incoming address can be
+redirected in several different ways:
+.numberpars $.
+It can be replaced by one or more new addresses which are themselves routed
+independently.
+.nextp
+It can be routed to be delivered to a given file or directory.
+.nextp
+It can be routed to be delivered to a specified pipe command.
+.nextp
+It can cause an automatic reply to be generated.
+.nextp
+It can be forced to fail, with a custom error message.
+.nextp
+It can be temporarily deferred.
+.nextp
+It can be discarded.
+.endp
+The generic \transport\ option must not be set for \%redirect%\ routers.
+However, there are some private options which define transports for delivery to
+files and pipes, and for generating autoreplies. See the \file@_transport\,
+\pipe@_transport\ and \reply@_transport\ descriptions below.
+
+
+.section Redirection data
+The router operates by interpreting a text string which it obtains either by
+expanding the contents of the \data\ option, or by reading the entire contents
+of a file whose name is given in the \file\ option. These two options are
+mutually exclusive. The first is commonly used for handling system aliases, in
+a configuration like this:
+.display asis
+system_aliases:
+ driver = redirect
+ data = ${lookup{$local_part}lsearch{/etc/aliases}}
+.endd
+.em
+If the lookup fails, the expanded string in this example is empty. When the
+expansion of \data\ results in an empty string, the router declines. A forced
+expansion failure also causes the router to decline; other expansion failures
+cause delivery to be deferred.
+.nem
+
+A configuration using \file\ is commonly used for handling users' \(.forward)\
+files, like this:
+.display asis
+userforward:
+ driver = redirect
+ check_local_user
+ file = $home/.forward
+ no_verify
+.endd
+If the file does not exist, or causes no action to be taken (for example, it is
+empty or consists only of comments), the router declines. \**Warning**\: This
+is not the case when the file contains syntactically valid items that happen to
+yield empty addresses, for example, items containing only RFC 2822 address
+comments.
+
+
+.section Forward files and address verification
+.index address redirection||while verifying
+It is usual to set \no@_verify\ on \%redirect%\ routers which handle users'
+\(.forward)\ files, as in the example above. There are two reasons for this:
+.numberpars $.
+When Exim is receiving an incoming SMTP message from a remote host, it is
+running under the Exim uid, not as root.
+No additional groups are set up, even if the Exim uid is a member of other
+groups (that is, the \*initgroups()*\ function is not run).
+Exim is unable to change uid to read the file as the user, and it may not be
+able to read it as the Exim user. So in practice the router may not be able to
+operate.
+.nextp
+However, even when the router can operate, the existence of a \(.forward)\ file
+is unimportant when verifying an address. What should be checked is whether the
+local part is a valid user name or not. Cutting out the redirection processing
+saves some resources.
+.endp
+
+
+
+
+.section Interpreting redirection data
+.index Sieve filter||specifying in redirection data
+.index filter||specifying in redirection data
+The contents of the data string, whether obtained from \data\ or \file\, can be
+interpreted in two different ways:
+.numberpars $.
+If the \allow@_filter\ option is set true, and the data begins with the text
+`@#Exim filter' or `@#Sieve filter', it is interpreted as a list of
+\*filtering*\ instructions in the form of an Exim or Sieve filter file,
+respectively. Details of the syntax and semantics of filter files are described
+in a separate document entitled \*Exim's interfaces to mail filtering*\; this
+document is intended for use by end users.
+.nextp
+Otherwise, the data must be a comma-separated list of redirection items, as
+described in the next section.
+.endp
+When a message is redirected to a file (a `mail folder'), the file name given
+in a non-filter redirection list must always be an absolute path. A filter may
+generate a relative path -- how this is handled depends on the transport's
+configuration. See section ~~SECTfildiropt for a discussion of this issue for
+the \%appendfile%\ transport.
+
+
+.section Items in a non-filter redirection list
+.rset SECTitenonfilred "~~chapter.~~section"
+.index address redirection||non-filter list items
+When the redirection data is not an Exim or Sieve filter, for example, if it
+comes from a conventional alias or forward file, it consists of a list of
+addresses, file names, pipe commands, or certain special items (see section
+~~SECTspecitredli below). The special items can be individually enabled or
+disabled by means of options whose names begin with \allow@_\ or \forbid@_\,
+depending on their default values. The items in the list are separated by
+commas or newlines.
+If a comma is required in an item, the entire item must be enclosed in double
+quotes.
+
+Lines starting with a @# character are comments, and are ignored, and @# may
+also appear following a comma, in which case everything between the @# and the
+next newline character is ignored.
+
+If an item is entirely enclosed in double quotes, these are removed. Otherwise
+double quotes are retained because some forms of mail address require their use
+(but never to enclose the entire address). In the following description, `item'
+refers to what remains after any surrounding double quotes have been removed.
+
+\**Warning**\: If you use an Exim expansion to construct a redirection address,
+and the expansion contains a reference to \$local@_part$\, you should make use
+of the \quote\ expansion operator, in case the local part contains special
+characters. For example, to redirect all mail for the domain
+\*obsolete.example*\, retaining the existing local part, you could use this
+setting:
+.display asis
+data = ${quote:$local_part}@newdomain.example
+.endd
+
+
+.section Redirecting to a local mailbox
+.rset SECTredlocmai "~~chapter.~~section"
+.index routing||loops in
+.index loop||while routing, avoidance of
+.index address redirection||to local mailbox
+A redirection item may safely be the same as the address currently under
+consideration. This does not cause a routing loop, because a router is
+automatically skipped if any ancestor of the address that is being processed
+.em
+is the same as the current address and was processed by the current router.
+.nem
+Such an address is therefore passed to the following routers, so it is handled
+as if there were no redirection. When making this loop-avoidance test, the
+complete local part, including any prefix or suffix, is used.
+
+.index address redirection||local part without domain
+Specifying the same local part without a domain is a common usage in personal
+filter files when the user wants to have messages delivered to the local
+mailbox and also forwarded elsewhere. For example, the user whose login is
+\*cleo*\ might have a \(.forward)\ file containing this:
+.display asis
+cleo, cleopatra@egypt.example
+.endd
+.index backslash in alias file
+.index alias file||backslash in
+For compatibility with other MTAs, such unqualified local parts may be
+preceeded by `@\', but this is not a requirement for loop prevention. However,
+it does make a difference if more than one domain is being handled
+synonymously.
+
+If an item begins with `@\' and the rest of the item parses as a valid RFC 2822
+address that does not include a domain, the item is qualified using the domain
+of the incoming address. In the absence of a leading `@\', unqualified
+addresses are qualified using the value in \qualify@_recipient\, but you can
+force the incoming domain to be used by setting \qualify__preserve@_domain\.
+
+Care must be taken if there are alias names for local users.
+.em
+Consider an MTA handling a single local domain where the system alias file
+contains:
+.display asis
+Sam.Reman: spqr
+.endd
+Now suppose that Sam (whose login id is \*spqr*\) wants to save copies of
+messages in the local mailbox, and also forward copies elsewhere. He creates
+this forward file:
+.display asis
+Sam.Reman, spqr@reme.elsewhere.example
+.endd
+With these settings, an incoming message addressed to \*Sam.Reman*\ fails. The
+\%redirect%\ router for system aliases does not process \*Sam.Reman*\ the
+second time round, because it has previously routed it,
+.nem
+and the following routers presumably cannot handle the alias. The forward file
+should really contain
+.display asis
+spqr, spqr@reme.elsewhere.example
+.endd
+but because this is such a common error, the \check@_ancestor\ option (see
+below) exists to provide a way to get round it. This is normally set on a
+\%redirect%\ router that is handling users' \(.forward)\ files.
+
+
+.section Special items in redirection lists
+.rset SECTspecitredli "~~chapter.~~section"
+In addition to addresses, the following types of item may appear in redirection
+lists (that is, in non-filter redirection data):
+
+.numberpars $.
+.index pipe||in redirection list
+.index address redirection||to pipe
+An item is treated as a pipe command if it begins with `|' and does not parse
+as a valid RFC 2822 address that includes a domain. A transport for running the
+command must be specified by the \pipe@_transport\ option.
+.em
+Normally, either the router or the transport specifies a user and a group under
+which to run the delivery. The default is to use the Exim user and group.
+.nem
+
+Single or double quotes can be used for enclosing the individual arguments of
+the pipe command; no interpretation of escapes is done for single quotes. If
+the command contains a comma character, it is necessary to put the whole item
+in double quotes, for example:
+.display asis
+"|/some/command ready,steady,go"
+.endd
+since items in redirection lists are terminated by commas. Do not, however,
+quote just the command. An item such as
+.display asis
+|"/some/command ready,steady,go"
+.endd
+is interpreted as a pipe with a rather strange command name, and no arguments.
+.nextp
+.index file||in redirection list
+.index address redirection||to file
+An item is interpreted as a path name if it begins with `/' and does not parse
+as a valid RFC 2822 address that includes a domain. For example,
+.display asis
+/home/world/minbari
+.endd
+is treated as a file name, but
+.display asis
+/s=molari/o=babylon/@x400gate.way
+.endd
+is treated as an address. For a file name, a transport must be specified using
+the \file@_transport\ option. However, if the generated path name ends with a
+forward slash character, it is interpreted as a directory name rather than a
+file name, and \directory@_transport\ is used instead.
+
+.em
+Normally, either the router or the transport specifies a user and a group under
+which to run the delivery. The default is to use the Exim user and group.
+.index \(/dev/null)\
+However, if a redirection item is the path \(/dev/null)\, delivery to it is
+bypassed at a high level, and the log entry shows `$*$$*$bypassed$*$$*$'
+instead of a transport name. In this case the user and group are not used.
+.nem
+.nextp
+.index included address list
+.index address redirection||included external list
+If an item is of the form
+.display
+:include:<<path name>>
+.endd
+a list of further items is taken from the given file and included at that
+point.
+\**Note**\: such a file can not be a filter file; it is just an out-of-line
+addition to the list.
+The items in the included list are separated by commas or newlines and are not
+subject to expansion. If this is the first item in an alias list in an
+\%lsearch%\ file, a colon must be used to terminate the alias name. This
+example is incorrect:
+.display asis
+list1 :include:/opt/lists/list1
+.endd
+It must be given as
+.display asis
+list1: :include:/opt/lists/list1
+.endd
+.nextp
+.index address redirection||to black hole
+Sometimes you want to throw away mail to a particular local part. Making the
+\data\ option expand to an empty string does not work, because that causes the
+router to decline. Instead, the alias item
+.index black hole
+.index abandoning mail
+.display
+:blackhole:
+.endd
+can be used. It does what its name implies. No delivery is done, and no error
+message is generated. This has the same effect as specifing \(/dev/null)\, but
+can be independently disabled.
+
+\**Warning**\: If \":blackhole:"\ appears anywhere in a redirection list, no
+delivery is done for the original local part, even if other redirection items
+are present. If you are generating a multi-item list (for example, by reading a
+database) and need the ability to provide a no-op item, you must use
+\(/dev/null)\.
+
+.nextp
+.index delivery||forcing failure
+.index delivery||forcing deferral
+.index failing delivery||forcing
+.index deferred delivery, forcing
+.index customizing||failure message
+An attempt to deliver a particular address can be deferred or forced to fail by
+redirection items of the form
+.display
+:defer:
+$rm{or}
+:fail:
+.endd
+respectively. When a redirection list contains such an item, it applies to the
+entire redirection; any other items in the list are ignored (:::blackhole:: is
+different). Any text following :::fail:: or :::defer:: is placed in the error
+text associated with the failure. For example, an alias file might contain:
+.display asis
+X.Employee: :fail: Gone away, no forwarding address
+.endd
+In the case of an address that is being verified from an ACL or as the subject
+of a \\VRFY\\ command, the text is included in the SMTP error response by
+default. In an ACL, an explicitly provided message overrides the default, but
+the default message is available in the variable \$acl@_verify@_message$\ and
+can therefore be included in a custom message if this is desired. Exim sends a
+451 SMTP code for a :::defer::, and 550 for :::fail::. In non-SMTP cases the
+text is included in the error message that Exim generates.
+
+
+
+Normally the error text is the rest of the redirection list -- a comma does not
+terminate it -- but a newline does act as a terminator. Newlines are not
+normally present in alias expansions. In \%lsearch%\ lookups they are removed as
+part of the continuation process, but they may exist in other kinds of lookup
+and in :::include:: files.
+
+During routing for message delivery (as opposed to verification), a redirection
+containing :::fail:: causes an immediate failure of the incoming address,
+whereas :::defer:: causes the message to remain on the queue so that a
+subsequent delivery attempt can happen at a later time. If an address is
+deferred for too long, it will ultimately fail, because the normal retry
+rules still apply.
+.nextp
+.index alias file||exception to default
+Sometimes it is useful to use a single-key search type with a default (see
+chapter ~~CHAPfdlookup) to look up aliases. However, there may be a need for
+exceptions to the default. These can be handled by aliasing them to
+.display asis
+:unknown:
+.endd
+This differs from :::fail:: in that it causes the \%redirect%\ router to decline,
+whereas :::fail:: forces routing to fail. A lookup which results in an empty
+redirection list has the same effect.
+.endp
+
+.section Duplicate addresses
+.index duplicate addresses
+.index address||duplicate, discarding
+.index pipe||duplicated
+Exim removes duplicate addresses from the list to which it is delivering, so as
+to deliver just one copy to each address. This does not apply to deliveries
+routed to pipes by different immediate parent addresses, but an indirect
+aliasing scheme of the type
+.display asis
+pipe: |/some/command $local_part
+localpart1: pipe
+localpart2: pipe
+.endd
+does not work with a message that is addressed to both local parts, because
+when the second is aliased to the intermediate local part `pipe' it gets
+discarded as being the same as a previously handled address. However, a scheme
+such as
+.display asis
+localpart1: |/some/command $local_part
+localpart2: |/some/command $local_part
+.endd
+does result in two different pipe deliveries, because the immediate parents of
+the pipes are distinct.
+
+
+.section Repeated redirection expansion
+.index repeated redirection expansion
+.index address redirection||repeated for each delivery attempt
+When a message cannot be delivered to all of its recipients immediately,
+leading to two or more delivery attempts, redirection expansion is carried out
+afresh each time for those addresses whose children were not all previously
+delivered. If redirection is being used as a mailing list, this can lead to new
+members of the list receiving copies of old messages. The \one@_time\ option
+can be used to avoid this.
+
+.section Errors in redirection lists
+.index address redirection||errors
+If \skip@_syntax@_errors\ is set, a malformed address that causes a parsing
+error is skipped, and an entry is written to the main log. This may be useful
+for mailing lists that are automatically managed. Otherwise, if an error is
+detected while generating the list of new addresses, the original address is
+deferred. See also \syntax@_errors@_to\.
+
+
+.section Private options for the redirect router
+
+The private options for the \%redirect%\ router are as follows:
+
+.startconf
+.index options||\%redirect%\ router
+
+.conf allow@_defer boolean false
+Setting this option allows the use of :::defer:: in non-filter redirection
+data,
+or the \defer\ command in an Exim filter file.
+
+.conf allow@_fail boolean false
+.index failing delivery||from filter
+If this option is true, the :::fail:: item can be used in a redirection list,
+and the \fail\ command may be used in a filter file.
+
+.conf allow@_filter boolean false
+.index filter||enabling use of
+.index Sieve filter||enabling use of
+Setting this option allows Exim to interpret redirection data that starts with
+`@#Exim filter' or `@#Sieve filter' as a set of filtering instructions. There
+are some features of Exim filter files that some administrators may wish to
+lock out; see the \forbid@_filter@_xxx\ options below. The filter is run using
+the uid and gid set by the generic \user\ and \group\ options. These take their
+defaults from the password data if \check@_local@_user\ is set, so in the
+normal case of users' personal filter files, the filter is run as the relevant
+user. When \allow@_filter\ is set true, Exim insists that either
+\check@_local@_user\ or \user\ is set.
+
+
+.conf allow@_freeze boolean false
+.index freezing messages||allowing in filter
+Setting this option allows the use of the \freeze\ command in an Exim filter.
+This command is more normally encountered in system filters, and is disabled by
+default for redirection filters because it isn't something you usually want to
+let ordinary users do.
+
+
+.conf check@_ancestor boolean false
+This option is concerned with handling generated addresses that are the same
+as some address in the list of redirection ancestors of the current address.
+Although it is turned off by default in the code, it is set in the default
+configuration file for handling users' \(.forward)\ files. It is recommended
+for this use of the \%redirect%\ router.
+
+.em
+When \check@_ancestor\ is set, if a generated address (including the domain) is
+the same as any ancestor of the current address, it is replaced by a copy of
+the current address. This helps in the case where local part A is aliased to B,
+and B has a \(.forward)\ file pointing back to A. For example, within a single
+domain, the local part `Joe.Bloggs' is aliased to `jb' and \(@~jb/.forward)\
+contains:
+.nem
+.display
+@\Joe.Bloggs, <<other item(s)>>
+.endd
+Without the \check@_ancestor\ setting, either local part (`jb' or `joe.bloggs')
+gets processed once by each router and so ends up as it was originally. If `jb'
+is the real mailbox name, mail to `jb' gets delivered (having been turned into
+`joe.bloggs' by the \(.forward)\ file and back to `jb' by the alias), but mail
+to `joe.bloggs' fails. Setting \check@_ancestor\ on the \%redirect%\ router that
+handles the \(.forward)\ file prevents it from turning `jb' back into
+`joe.bloggs' when that was the original address. See also the \repeat@_use\
+option below.
+
+.conf check@_group boolean "see below"
+When the \file\ option is used, the group owner of the file is checked only
+when this option is set. The permitted groups are those listed in the
+\owngroups\ option, together with the user's default group if
+\check@_local@_user\ is set. If the file has the wrong group, routing is
+deferred. The default setting for this option is true if \check@_local@_user\
+is set and the \modemask\ option permits the group write bit, or if the
+\owngroups\ option is set. Otherwise it is false, and no group check occurs.
+
+
+.conf check@_owner boolean "see below"
+When the \file\ option is used, the owner of the file is checked only when this
+option is set. If \check@_local@_user\ is set, the local user is permitted;
+otherwise the owner must be one of those listed in the \owners\ option. The
+default value for this option is true if \check@_local@_user\ or \owners\ is
+set. Otherwise the default is false, and no owner check occurs.
+
+.conf data string$**$ unset
+This option is mutually exclusive with \file\. One or other of them must be
+set, but not both. The contents of \data\ are expanded, and then used as the
+list of forwarding items, or as a set of filtering instructions. If the
+expansion is forced to fail, or the result is an empty string or a string that
+has no effect (consists entirely of comments), the router declines.
+
+When filtering instructions are used, the string must begin with `@#Exim
+filter', and all comments in the string, including this initial one, must be
+terminated with newline characters. For example:
+.display asis
+data = #Exim filter\n\
+ if $h_to: contains Exim then save $home/mail/exim endif
+.endd
+If you are reading the data from a database where newlines cannot be included,
+you can use the \$@{sg@}$\ expansion item to turn the escape string of your
+choice into a newline.
+
+.conf directory@_transport string$**$ unset
+A \%redirect%\ router sets up a direct delivery to a directory when a path name
+ending with a slash is specified as a new `address'. The transport used is
+specified by this option, which, after expansion, must be the name of a
+configured transport. This should normally be an \%appendfile%\ transport.
+
+.conf file string$**$ unset
+This option specifies the name of a file that contains the redirection data. It
+is mutually exclusive with the \data\ option. The string is expanded before
+use; if the expansion is forced to fail, the router declines. Other expansion
+failures cause delivery to be deferred. The result of a successful expansion
+must be an absolute path. The entire file is read and used as the redirection
+data. If the data is an empty string or a string that has no effect (consists
+entirely of comments), the router declines.
+
+.index NFS||checking for file existence
+If the attempt to open the file fails with a `does not exist' error, Exim
+runs a check on the containing directory,
+unless \ignore@_enotdir\ is true (see below).
+If the directory does not appear to exist, delivery is deferred. This can
+happen when users' \(.forward)\ files are in NFS-mounted directories, and there
+is a mount problem. If the containing directory does exist, but the file does
+not, the router declines.
+
+.conf file@_transport string$**$ unset
+A \%redirect%\ router sets up a direct delivery to a file when a path name not
+ending in a slash is specified as a new `address'. The transport used is
+specified by this option, which, after expansion, must be the name of a
+configured transport.
+This should normally be an \%appendfile%\ transport.
+When it is running, the file name is in \$address@_file$\.
+
+.conf forbid@_blackhole boolean false
+If this option is true, the :::blackhole:: item may not appear in a redirection
+list.
+
+.conf forbid@_file boolean false
+.index delivery||to file, forbidding
+.index Sieve filter||forbidding delivery to a file
+.index Sieve filter||`keep' facility, disabling
+If this option is true, this router may not generate a new address that
+specifies delivery to a local file or directory, either from a filter or from a
+conventional forward file. This option is forced to be true if \one@_time\ is
+set. It applies to Sieve filters as well as to Exim filters, but if true, it
+locks out the Sieve's `keep' facility.
+
+.conf forbid@_filter@_existstest boolean false
+.index filter||locking out certain features
+If this option is true, string expansions in Exim filters are not allowed to
+make use of the \exists\ condition.
+
+.conf forbid@_filter@_logwrite boolean false
+If this option is true, use of the logging facility in Exim filters is not
+permitted. Logging is in any case available only if the filter is being run
+under some unprivileged uid (which is normally the case for ordinary users'
+\(.forward)\ files).
+
+.conf forbid@_filter@_lookup boolean false
+If this option is true, string expansions in Exim filter files are not allowed
+to make use of \lookup\ items.
+
+.conf forbid@_filter@_perl boolean false
+This option is available only if Exim is built with embedded Perl support. If
+it is true, string expansions in Exim filter files are not allowed to make use
+of the embedded Perl support.
+
+.conf forbid@_filter@_readfile boolean false
+If this option is true, string expansions in Exim filter files are not allowed
+to make use of \readfile\ items.
+
+.conf forbid@_filter@_readsocket boolean false
+If this option is true, string expansions in Exim filter files are not allowed
+to make use of \readsocket\ items.
+
+.conf forbid@_filter@_reply boolean false
+If this option is true, this router may not generate an automatic reply
+message. Automatic replies can be generated only from Exim filter files, not
+from traditional forward files or Sieve filters. This option is forced to be
+true if \one@_time\ is set.
+
+.conf forbid@_filter@_run boolean false
+If this option is true, string expansions in Exim filter files are not allowed
+to make use of \run\ items.
+
+.conf forbid@_include boolean false
+If this option is true, items of the form
+.display
+:include:<<path name>>
+.endd
+are not permitted in non-filter redirection lists.
+
+.conf forbid@_pipe boolean false
+.index delivery||to pipe, forbidding
+If this option is true, this router may not generate a new address which
+specifies delivery to a pipe, either from an Exim filter or from a conventional
+forward file. This option is forced to be true if \one@_time\ is set.
+
+.conf hide@_child@_in@_errmsg boolean false
+.index bounce message||redirection details, suppressing
+If this option is true, it prevents Exim from quoting a child address if it
+generates a bounce or delay message for it. Instead it says `an address
+generated from <<the top level address>>'. Of course, this applies only to
+bounces generated locally. If a message is forwarded to another host, $it{its}
+bounce may well quote the generated address.
+
+.conf ignore@_eacces boolean false
+.index \\EACCES\\
+If this option is set and an attempt to open a redirection file yields the
+\\EACCES\\ error (permission denied), the \%redirect%\ router behaves as if the
+file did not exist.
+
+.conf ignore@_enotdir boolean false
+.index \\ENOTDIR\\
+If this option is set and an attempt to open a redirection file yields the
+\\ENOTDIR\\ error (something on the path is not a directory), the \%redirect%\
+router behaves as if the file did not exist.
+
+Setting \ignore@_enotdir\ has another effect as well: When a \%redirect%\
+router that has the \file\ option set discovers that the file does not exist
+(the \\ENOENT\\ error), it tries to \*stat()*\ the parent directory, as a check
+against unmounted NFS directories. If the parent can not be statted, delivery
+is deferred. However, it seems wrong to do this check when \ignore@_enotdir\ is
+set, because that option tells Exim to ignore `something on the path is not a
+directory' (the \\ENOTDIR\\ error). This is a confusing area, because it seems
+that some operating systems give \\ENOENT\\ where others give \\ENOTDIR\\.
+
+
+.conf include@_directory string unset
+If this option is set, the path names of any :::include:: items in a redirection
+list must start with this directory.
+
+.conf modemask "octal integer" 022
+This specifies mode bits which must not be set for a file specified by the
+\file\ option. If any of the forbidden bits are set, delivery is deferred.
+
+.conf one@_time boolean false
+.index one-time aliasing/forwarding expansion
+.index alias file||one-time expansion
+.index forward file||one-time expansion
+.index mailing lists||one-time expansion
+.index address redirection||one-time expansion
+Sometimes the fact that Exim re-evaluates aliases and reprocesses redirection
+files each time it tries to deliver a message causes a problem
+when one or more of the generated addresses fails be delivered at the first
+attempt. The problem is not one of duplicate delivery -- Exim is clever enough
+to handle that -- but of what happens when the redirection list changes during
+the time that the message is on Exim's queue. This is particularly true in the
+case of mailing lists, where new subscribers might receive copies of messages
+that were posted before they subscribed.
+
+If \one@_time\ is set and any addresses generated by the router fail to
+deliver at the first attempt, the failing addresses are added to the message as
+`top level' addresses, and the parent address that generated them is marked
+`delivered'. Thus, redirection does not happen again at the next
+delivery attempt.
+
+\**Warning 1**\: This means that any header line addition or removal that is
+specified by this router would be lost if delivery did not succeed at the
+first attempt. For this reason, the \headers@_add\ and \headers@_remove\
+generic options are not permitted when \one@_time\ is set.
+
+\**Warning 2**\: To ensure that the router generates only addresses (as opposed
+to pipe or file deliveries or auto-replies) \forbid@_file\, \forbid@_pipe\,
+and \forbid@_filter@_reply\ are forced to be true when \one@_time\ is set.
+
+The original top-level address is remembered with each of the generated
+addresses, and is output in any log messages. However, any intermediate parent
+addresses are not recorded. This makes a difference to the log only if
+\all__parents\ log selector is set. It is expected that \one@_time\ will
+typically be used for mailing lists, where there is normally just one level of
+expansion.
+
+.conf owners "string list" unset
+.index ownership||alias file
+.index ownership||forward file
+.index alias file||ownership
+.index forward file||ownership
+This specifies a list of permitted owners for the file specified by \file\.
+This list is in addition to the local user when \check@_local@_user\ is set.
+See \check@_owner\ above.
+
+.conf owngroups "string list" unset
+This specifies a list of permitted groups for the file specified by \file\. The
+list is in addition to the local user's primary group when \check@_local@_user\
+is set. See \check@_group\ above.
+
+.em
+.conf qualify@_domain string$**$ unset
+If this option is set and an unqualified address (one without a domain) is
+generated, it is qualified with the domain specified by expanding this string,
+instead of the global setting in \qualify@_recipient\. If the expansion fails,
+the router declines. If you want to revert to the default, you can have the
+expansion generate \$qualify@_recipient$\.
+.nem
+
+.conf pipe@_transport string$**$ unset
+A \%redirect%\ router sets up a direct delivery to a pipe when a string starting
+with a vertical bar character is specified as a new `address'. The transport
+used is specified by this option, which, after expansion, must be the name of a
+configured transport.
+This should normally be a \%pipe%\ transport.
+When the transport is run, the pipe command is in \$address@_pipe$\.
+
+.conf qualify@_preserve@_domain boolean false
+.index domain||in redirection, preserving
+.index preserving domain in redirection
+.index address redirection||domain, preserving
+If this is set and an unqualified address (one without a domain) is generated,
+it is qualified with the domain of the
+.em
+parent address (the immediately preceding ancestor) instead of the local
+\qualify@_domain\ or global \qualify@_recipient\ value.
+.nem
+
+.conf repeat@_use boolean true
+If this option is set false, the router is skipped for a child address that has
+any ancestor that was routed by this router. This test happens before any of
+the other preconditions are tested. Exim's default anti-looping rules skip
+only when the ancestor is the same as the current address. See also
+\check@_ancestor\ above and the generic \redirect@_router\ option.
+
+.conf reply@_transport string$**$ unset
+A \%redirect%\ router sets up an automatic reply when a \mail\ or \vacation\
+command is used in a filter file. The transport used is specified by this
+option, which, after expansion, must be the name of a configured transport.
+This should normally be an \%autoreply%\ transport. Other transports are
+unlikely to do anything sensible or useful.
+
+.conf rewrite boolean true
+.index address redirection||disabling rewriting
+If this option is set false, addresses generated by the router are not
+subject to address rewriting. Otherwise, they are treated like new addresses
+and are rewritten according to the global rewriting rules.
+
+.conf skip@_syntax@_errors boolean false
+.index forward file||broken
+.index address redirection||broken files
+.index alias file||broken
+.index broken alias or forward files
+.index ignoring faulty addresses
+.index skipping faulty addresses
+.index error||skipping bad syntax
+If \skip@_syntax@_errors\ is set, syntactically malformed addresses in
+non-filter redirection data are skipped, and each failing address is logged. If
+\syntax@_errors@_to\ is set, a message is sent to the address it defines,
+giving details of the failures. If \syntax@_errors@_text\ is set, its contents
+are expanded and placed at the head of the error message generated by
+\syntax@_errors@_to\. Usually it is appropriate to set \syntax@_errors@_to\ to
+be the same address as the generic \errors@_to\ option. The
+\skip@_syntax@_errors\ option is often used when handling mailing lists.
+
+If all the addresses in a redirection list are skipped because of syntax
+errors, the router declines to handle the original address, and it is passed to
+the following routers.
+
+If \skip@_syntax@_errors\ is set when an Exim filter is interpreted, any syntax
+error in the filter causes filtering to be abandoned without any action being
+taken. The incident is logged, and the router declines to handle the address,
+so it is passed to the following routers.
+
+.index Sieve filter||syntax errors in
+Currently, any syntax errors in a Sieve filter file cause the `keep' action to
+occur. The values of \skip@_syntax@_errors\, \syntax@_errors@_to\, and
+\syntax@_errors@_text\ are not used.
+
+\skip@_syntax@_errors\ can be used to specify that errors in users' forward
+lists or filter files should not prevent delivery. The \syntax@_errors@_to\
+option, used with an address that does not get redirected, can be used to
+notify users of these errors, by means of a router like this:
+.display flow asis
+userforward:
+ driver = redirect
+ allow_filter
+ check_local_user
+ file = $home/.forward
+ file_transport = address_file
+ pipe_transport = address_pipe
+ reply_transport = address_reply
+ no_verify
+ skip_syntax_errors
+ syntax_errors_to = real-$local_part@$domain
+ syntax_errors_text = \
+ This is an automatically generated message. An error has\n\
+ been found in your .forward file. Details of the error are\n\
+ reported below. While this error persists, you will receive\n\
+ a copy of this message for every message that is addressed\n\
+ to you. If your .forward file is a filter file, or if it is\n\
+ a non-filter file containing no valid forwarding addresses,\n\
+ a copy of each incoming message will be put in your normal\n\
+ mailbox. If a non-filter file contains at least one valid\n\
+ forwarding address, forwarding to the valid addresses will\n\
+ happen, and those will be the only deliveries that occur.
+.endd
+You also need a router to ensure that local addresses that are prefixed by
+\"real-"\ are recognized, but not forwarded or filtered. For example, you could
+put this immediately before the \%userforward%\ router:
+.display asis
+real_localuser:
+ driver = accept
+ check_local_user
+ local_part_prefix = real-
+ transport = local_delivery
+.endd
+
+.conf syntax@_errors@_text string$**$ unset
+See \skip@_syntax@_errors\ above.
+
+.conf syntax@_errors@_to string unset
+See \skip@_syntax@_errors\ above.
+
+.endconf
+
+
+
+
+
+.
+.
+.
+. ============================================================================
+.chapter Environment for running local transports
+.rset CHAPenvironment "~~chapter"
+.set runningfoot "local transport environment"
+.index local transports||environment for
+.index environment for local transports
+.index transport||local, environment for
+Local transports handle deliveries to files and pipes. (The \%autoreply%\
+transport can be thought of as similar to a pipe.) Exim always runs transports
+in subprocesses, under specified uids and gids. Typical deliveries to local
+mailboxes run under the uid and gid of the local user.
+
+Exim also sets a specific current directory while running the transport; for
+some transports a home directory setting is also relevant. The \%pipe%\
+transport is the only one which sets up environment variables; see section
+~~SECTpipeenv for details.
+
+The values used for the uid, gid, and the directories may come from several
+different places. In many cases, the router that handles the address associates
+settings with that address as a result of its \check@_local@_user\, \group\, or
+\user\ options. However, values may also be given in the transport's own
+configuration, and these override anything that comes from the router.
+
+.section Uids and gids
+.rset SECTenvuidgid "~~chapter.~~section"
+.index local transports||uid and gid
+.index transport||local, uid and gid
+All transports have the options \group\ and \user\. If \group\ is set, it
+overrides any group that the router set in the address, even if \user\ is not
+set for the transport. This makes it possible, for example, to run local mail
+delivery under the uid of the recipient (set by the router), but in a special
+group (set by the transport). For example:
+.display asis
+# Routers ...
+# User/group are set by check_local_user in this router
+local_users:
+ driver = accept
+ check_local_user
+ transport = group_delivery
+
+# Transports ...
+# This transport overrides the group
+group_delivery:
+ driver = appendfile
+ file = /var/spool/mail/$local_part
+ group = mail
+.endd
+If \user\ is set for a transport, its value overrides what is set in the
+address. If \user\ is non-numeric and \group\ is not set, the gid associated
+with the user is used. If \user\ is numeric, \group\ must be set.
+
+.index \initgroups\ option
+When the uid is taken from the transport's configuration, the \*initgroups()*\
+function is called for the groups associated with that uid if the \initgroups\
+option is set for the transport. When the uid is not specified by the
+transport, but is associated with the address by a router, the option for
+calling \*initgroups()*\ is taken from the router configuration.
+
+.index \%pipe%\ transport||uid for
+The \%pipe%\ transport contains the special option \pipe@_as@_creator\. If this
+is set and \user\ is not set, the uid of the process that called Exim to
+receive the message is used, and if \group\ is not set, the corresponding
+original gid is also used.
+
+
+.section Current and home directories
+.index current directory for local transport
+.index home directory||for local transport
+.index transport||local, home directory for
+.index transport||local, current directory for
+Routers may set current and home directories for local transports by means of
+the \transport__current@_directory\ and \transport@_home@_directory\ options.
+However, if the transport's \current__directory\ or \home@_directory\ options
+are set, they override the router's values. In detail, the home directory
+for a local transport is taken from the first of these values that is set:
+.numberpars $.
+The \home@_directory\ option on the transport;
+.nextp
+The \transport@_home@_directory\ option on the router;
+.nextp
+The password data if \check@_local@_user\ is set on the router;
+.nextp
+The \router@_home@_directory\ option on the router.
+.endp
+The current directory is taken from the first of these values that is set:
+.numberpars $.
+The \current@_directory\ option on the transport;
+.nextp
+The \transport@_current@_directory\ option on the router.
+.endp
+
+If neither the router nor the transport sets a current directory, Exim uses the
+value of the home directory, if it is set. Otherwise it sets the current
+directory to \(/)\ before running a local transport.
+
+
+.section Expansion variables derived from the address
+Normally a local delivery is handling a single address, and in that case the
+variables such as \$domain$\ and \$local@_part$\ are set during local
+deliveries. However, in some circumstances more than one address may be handled
+at once (for example, while writing batch SMTP for onward transmission by some
+other means). In this case, the variables associated with the local part are
+never set, \$domain$\ is set only if all the addresses have the same
+domain, and \$original@_domain$\ is never set.
+
+
+
+
+
+
+
+.
+.
+.
+. ============================================================================
+.chapter Generic options for transports
+.rset CHAPtransportgeneric "~~chapter"
+.set runningfoot "generic transport options"
+
+.index generic options||transport
+.index options||generic, for transports
+.index transport||generic options for
+The following generic options apply to all transports:
+
+.startconf
+.conf body@_only boolean false
+.index transport||body only
+.index message||transporting body only
+.index body of message||transporting
+If this option is set, the message's headers are not transported. It is
+mutually exclusive with \headers@_only\. If it is used with the \%appendfile%\ or
+\%pipe%\ transports, the settings of \message@_prefix\ and \message@_suffix\
+should be checked, because this option does not automatically suppress them.
+
+.conf current@_directory string$**$ unset
+.index transport||current directory for
+This specifies the current directory that is to be set while running the
+transport, overriding any value that may have been set by the router.
+If the expansion fails for any reason, including forced failure, an error is
+logged, and delivery is deferred.
+
+.conf disable@_logging boolean false
+If this option is set true, nothing is logged for any
+.em
+deliveries by the transport or for any
+.nem
+transport errors. You should not set this option unless you really, really know
+what you are doing.
+
+.conf debug@_print string$**$ unset
+.index testing||variables in drivers
+If this option is set and debugging is enabled (see the \-d-\ command line
+option), the string is expanded and included in the debugging output when the
+transport is run.
+If expansion of the string fails, the error message is written to the debugging
+output, and Exim carries on processing.
+This facility is provided to help with checking out the values of variables and
+so on when debugging driver configurations. For example, if a \headers@_add\
+option is not working properly, \debug@_print\ could be used to output the
+variables it references. A newline is added to the text if it does not end with
+one.
+
+.conf delivery@_date@_add boolean false
+.index ::Delivery-date:: header line
+If this option is true, a ::Delivery-date:: header is added to the message. This
+gives the actual time the delivery was made. As this is not a standard header,
+Exim has a configuration option (\delivery@_date@_remove\) which requests its
+removal from incoming messages, so that delivered messages can safely be resent
+to other recipients.
+
+.conf driver string unset
+This specifies which of the available transport drivers is to be used.
+There is no default, and this option must be set for every transport.
+
+.conf envelope@_to@_add boolean false
+.index ::Envelope-to:: header line
+If this option is true, an ::Envelope-to:: header is added to the message. This
+gives the original address(es) in the incoming envelope that caused this
+delivery to happen. More than one address may be present if the transport is
+configured to handle several addresses at once, or if more than one original
+address was redirected to the same final address. As this is not a standard
+header, Exim has a configuration option (\envelope@_to@_remove\) which requests
+its removal from incoming messages, so that delivered messages can safely be
+resent to other recipients.
+
+.conf group string$**$ "Exim group"
+.index transport||group, specifying
+This option specifies a gid for running the transport process, overriding any
+value that the router supplies, and also overriding any value associated with
+\user\ (see below).
+
+.conf headers@_add string$**$ unset
+.index header lines||adding in transport
+.index transport||header lines, adding
+This option specifies a string of text which is expanded and added to the
+header portion of a message as it is transported. If the result of the
+expansion is an empty string, or if the expansion is forced to fail, no action
+is taken. Other expansion failures are treated as errors and cause the delivery
+to be deferred. The expanded string should be in the form of one or more RFC
+2822 header lines, separated by newlines (coded as `@\n'), for example:
+.display asis
+headers_add = X-added: this is a header added at $tod_log\n\
+ X-added: this is another
+.endd
+Exim does not check the syntax of these added header lines. They are added at
+the end of the existing header lines. If you include a blank line within the
+string, you can subvert this facility into adding text at the start of the
+message's body. This is not recommended. Additional header lines can also be
+specified by routers. See chapter ~~CHAProutergeneric and section
+~~SECTheadersaddrem.
+
+.conf headers@_only boolean false
+.index transport||header lines only
+.index message||transporting headers only
+.index header lines||transporting
+If this option is set, the message's body is not transported. It is mutually
+exclusive with \body@_only\. If it is used with the \%appendfile%\ or \%pipe%\
+transports, the settings of \message@_prefix\ and \message__suffix\ should be
+checked, since this option does not automatically suppress them.
+
+.conf headers@_remove string$**$ unset
+.index header lines||removing
+.index transport||header lines, removing
+This option is expanded; the result must consist of a colon-separated list of
+header names, not including the terminating colon, for example:
+.display asis
+headers_remove = return-receipt-to:acknowledge-to
+.endd
+Any existing headers matching those names are not included in any message that
+is transmitted by the transport.
+If the result of the expansion is an empty string, or if the expansion is
+forced to fail, no action is taken. Other expansion failures are treated as
+errors and cause the delivery to be deferred.
+
+If there are multiple instances of a header, they are all removed. However,
+added headers may have these names. Thus it is possible to replace a header by
+specifying it in \headers@_remove\ and supplying the replacement in
+\headers@_add\. Headers to be removed can also be specified by routers. See
+chapter ~~CHAProutergeneric and section ~~SECTheadersaddrem.
+
+.conf headers@_rewrite string unset
+.index transport||header lines, rewriting
+.index rewriting||at transport time
+This option allows addresses in header lines to be rewritten at transport time,
+that is, as the message is being copied to its destination. The contents of the
+option are a colon-separated list of rewriting rules. Each rule is in exactly
+the same form as one of the general rewriting rules that are applied when a
+message is received. These are described in chapter ~~CHAPrewrite. For example,
+.display asis
+headers_rewrite = a@b c@d f : \
+ x@y w@z
+.endd
+changes \a@@b\ into \c@@d\ in ::From:: header lines, and \x@@y\ into \w@@z\ in
+all address-bearing header lines. The rules are applied to the header lines
+just before they are written out at transport time, so they affect only those
+copies of the message that pass through the transport. However, only the
+message's original header lines, and any that were added by a system filter,
+are rewritten. If a router or transport adds header lines, they are
+not affected by this option. These rewriting rules are $it{not} applied to the
+envelope. You can change the return path using \return@_path\, but you cannot
+change envelope recipients at this time.
+
+.conf home@_directory string$**$ unset
+.index transport||home directory for
+This option specifies a home directory setting for the transport, overriding
+any value that may be set by the router. The home directory is placed in
+\$home$\ while expanding the transport's private options. It is also used as
+the current directory if no current directory is set by the
+\current__directory\ option on the transport or the
+\transport__current__directory\ option on the router.
+If the expansion fails for any reason, including forced failure, an error is
+logged, and delivery is deferred.
+
+
+.index additional groups
+.index groups, additional
+.index transport||group, additional
+.conf initgroups boolean false
+If this option is true and the uid for the delivery process is provided by the
+transport, the \*initgroups()*\ function is called when running the transport
+to ensure that any additional groups associated with the uid are set up.
+
+.conf message@_size@_limit string$**$ 0
+.index limit||message size per transport
+.index size||of message, limit
+.index transport||message size, limiting
+This option controls the size of messages passed through the transport. It is
+expanded before use; the result of the expansion must be a sequence of digits,
+optionally followed by K or M.
+If the expansion fails for any reason, including forced failure, or if the
+result is not of the required form, delivery is deferred.
+If the value is greater than zero and the size of a message exceeds this
+limit, the address is failed. If there is any chance that the resulting bounce
+message could be routed to the same transport, you should ensure that
+\return@_size@_limit\ is less than the transport's \message@_size@_limit\, as
+otherwise the bounce message will fail to get delivered.
+
+
+.conf rcpt@_include@_affixes boolean false
+.index prefix||for local part, including in envelope
+.index suffix||for local part, including in envelope
+.index local part||prefix
+.index local part||suffix
+When this option is false (the default), and an address that has had any
+affixes (prefixes or suffixes) removed from the local part is delivered by any
+form of SMTP or LMTP, the affixes are not included. For example, if a router
+that contains
+.display asis
+local_part_prefix = *-
+.endd
+routes the address \*abc-xyz@@some.domain*\ to an SMTP transport, the envelope
+is delivered with
+.display asis
+RCPT TO:<xyz@some.domain>
+.endd
+If \rcpt@_include@_affixes\ is set true, the whole local part is included in
+the \\RCPT\\ command. This option applies to BSMTP deliveries by the
+\%appendfile%\ and \%pipe%\ transports as well as to the \%lmtp%\ and \%smtp%\
+transports.
+
+.conf retry@_use@_local@_part boolean "see below"
+.index hints database||retry keys
+When a delivery suffers a temporary failure, a retry record is created
+in Exim's hints database. For remote deliveries, the key for the retry record
+is based on the name and/or IP address of the failing remote host. For local
+deliveries, the key is normally the entire address, including both the local
+part and the domain. This is suitable for most common cases of local delivery
+temporary failure -- for example, exceeding a mailbox quota should delay only
+deliveries to that mailbox, not to the whole domain.
+
+However, in some special cases you may want to treat a temporary local delivery
+as a failure associated with the domain, and not with a particular local part.
+(For example, if you are storing all mail for some domain in files.) You can do
+this by setting \retry@_use@_local@_part\ false.
+
+For all the local transports, its default value is true. For remote transports,
+the default value is false for tidiness, but changing the value has no effect
+on a remote transport in the current implementation.
+
+.conf return@_path string$**$ unset
+.index envelope sender
+.index transport||return path, changing
+.index return path||changing in transport
+If this option is set, the string is expanded at transport time and replaces
+the existing return path (envelope sender) value in the copy of the message
+that is being delivered. An empty return path is permitted. This feature is
+designed for remote deliveries, where the value of this option is used in the
+SMTP \\MAIL\\ command. If you set \return@_path\ for a local transport, the
+only effect is to change the address that is placed in the ::Return-path::
+header line, if one is added to the message (see the next option).
+
+The expansion can refer to the existing value via \$return@_path$\. This is
+either the message's envelope sender, or an address set by the
+\errors@_to\ option on a router. If the expansion is forced to fail, no
+replacement occurs; if it fails for another reason, delivery is deferred. This
+option can be used to support VERP (Variable Envelope Return Paths) -- see
+chapter ~~CHAPSMTP.
+
+\**Note**\: If a delivery error is detected locally,
+.em
+including the case when a remote server rejects a message at SMTP time,
+the bounce message is not sent to the value of this option, but to the
+previously set errors address (which defaults to the incoming sender address).
+.nem
+
+
+.conf return@_path@_add boolean false
+.index ::Return-path:: header line
+If this option is true, a ::Return-path:: header is added to the message.
+Although the return path is normally available in the prefix line of BSD
+mailboxes, this is commonly not displayed by MUAs, and so the user does not
+have easy access to it.
+
+RFC 2821 states that the ::Return-path:: header is added to a message `when the
+delivery SMTP server makes the final delivery'. This implies that this header
+should not be present in incoming messages. Exim has a configuration option,
+\return@_path@_remove\, which requests removal of this header from incoming
+messages, so that delivered messages can safely be resent to other recipients.
+
+.conf shadow@_condition string$**$ unset
+See \shadow@_transport\ below.
+
+.conf shadow@_transport string unset
+.index shadow transport
+.index transport||shadow
+A local transport may set the \shadow@_transport\ option to the name of another
+local transport. Shadow remote transports are not supported.
+
+Whenever a delivery to the main transport succeeds, and either
+\shadow@_condition\ is unset, or its expansion does not result in the empty
+string or one of the strings `0' or `no' or `false', the message is also passed
+to the shadow transport, with the same delivery address or addresses.
+If expansion fails, no action is taken except that non-forced expansion
+failures cause a log line to be written.
+
+The result of the shadow transport is discarded and does not affect the
+subsequent processing of the message. Only a single level of shadowing is
+provided; the \shadow@_transport\ option is ignored on any transport when it is
+running as a shadow. Options concerned with output from pipes are also ignored.
+
+The log line for the successful delivery has an item added on the end, of the
+form
+.display
+ST=<<shadow transport name>>
+.endd
+If the shadow transport did not succeed, the error message is put in
+parentheses afterwards.
+
+Shadow transports can be used for a number of different purposes, including
+keeping more detailed log information than Exim normally provides, and
+implementing automatic acknowledgement policies based on message headers that
+some sites insist on.
+
+.conf transport@_filter string$**$ unset
+.index transport||filter
+.index filter||transport filter
+This option sets up a filtering (in the Unix shell sense) process for messages
+at transport time. It should not be confused with mail filtering as set up by
+individual users or via a system filter.
+
+When the message is about to be written out, the command specified by
+\transport@_filter\ is started up in a separate process, and the entire
+message, including the header lines, is passed to it on its standard input
+(this in fact is done from a third process, to avoid deadlock).
+The command must be specified as an absolute path.
+
+The message is passed to the filter before any SMTP-specific processing, such
+as turning `@\n' into `@\r@\n' and escaping lines beginning with a dot, and
+also before any processing implied by the settings of \check@_string\ and
+\escape@_string\ in the \%appendfile%\ or \%pipe%\ transports.
+
+The filter's standard output is read and written to the message's destination.
+The filter can perform any transformations it likes, but of course should take
+care not to break RFC 2822 syntax. A demonstration Perl script is provided in
+\(util/transport-filter.pl)\; this makes a few arbitrary modifications just to
+show the possibilities. Exim does not check the result, except to test for a
+final newline when SMTP is in use. All messages transmitted over SMTP must end
+with a newline, so Exim supplies one if it is missing.
+
+.index SMTP||\\SIZE\\
+A problem might arise if the filter increases the size of a message that is
+being sent down an SMTP connection. If the receiving SMTP server has indicated
+support for the \\SIZE\\ parameter, Exim will have sent the size of the message
+at the start of the SMTP session. If what is actually sent is substantially
+more, the server might reject the message. This can be worked round by setting
+the \size@_addition\ option on the \%smtp%\ transport, either to allow for
+additions to the message, or to disable the use of \\SIZE\\ altogether.
+
+The value of the option is the command string for starting up the filter, which
+is run directly from Exim, not under a shell. The string is parsed by Exim in
+the same way as a command string for the \%pipe%\ transport: Exim breaks it up
+into arguments and then expands each argument separately. The special argument
+\$pipe@_addresses$\ is replaced by a number of arguments, one for each address
+that applies to this delivery. (This isn't an ideal name for this feature here,
+but as it was already implemented for the \%pipe%\ transport, it seemed sensible
+not to change it.)
+
+.index \$host$\
+.index \$host@_address$\
+The expansion variables \$host$\ and \$host@_address$\ are available when the
+transport is a remote one. They contain the name and IP address of the host to
+which the message is being sent. For example:
+.display asis
+transport_filter = /some/directory/transport-filter.pl \
+ $host $host_address $sender_address $pipe_addresses
+.endd
+The filter process is run under the same uid and gid as the normal delivery.
+For remote deliveries this is the Exim uid/gid by default.
+
+If a transport filter is set on an autoreply transport, the original message is
+passed through the filter as it is being copied into the newly generated
+message, which happens if the \return@_message\ option is set.
+
+.conf transport@_filter@_timeout time 5m
+.index transport||filter, timeout
+When Exim is reading the output of a transport filter, it a applies a timeout
+that can be set by this option. Exceeding the timeout is treated as a
+temporary delivery failure.
+
+
+.conf user string$**$ "Exim user"
+.index uid (user id)||local delivery
+.index transport||user, specifying
+This option specifies the user under whose uid the delivery process is to be
+run, overriding any uid that may have been set by the router. If the user is
+given as a name, the uid is looked up from the password data, and the
+associated group is taken as the value of the gid to be used if the \group\
+option is not set.
+
+.em
+For deliveries that use local transports, a user and group are normally
+specified explicitly or implicitly (for example, as a result of
+\check@_local@_user\) by the router or transport.
+.nem
+
+.index hints database||access by remote transport
+For remote transports, you should leave this option unset unless you really are
+sure you know what you are doing. When a remote transport is running, it needs
+to be able to access Exim's hints databases, because each host may have its own
+retry data.
+
+.endconf
+
+
+
+
+
+.
+.
+.
+. ============================================================================
+.chapter Address batching in local transports
+.set runningfoot "address batching"
+.rset CHAPbatching ~~chapter
+.index transport||local, address batching in
+The only remote transport (\%smtp%\) is normally configured to handle more than
+one address at a time, so that when several addresses are routed to the same
+remote host, just one copy of the message is sent. Local transports, however,
+normally handle one address at a time. That is, a separate instance of the
+transport is run for each address that is routed to the transport. A separate
+copy of the message is delivered each time.
+
+.index batched local delivery
+.index \batch@_max\
+.index \batch@_id\
+In special cases, it may be desirable to handle several addresses at once in a
+local transport, for example:
+.numberpars $.
+In an \%appendfile%\ transport, when storing messages in files for later
+delivery by some other means, a single copy of the message with multiple
+recipients saves space.
+.nextp
+In an \%lmtp%\ transport, when delivering over `local SMTP' to some process,
+a single copy saves time, and is the normal way LMTP is expected to work.
+.nextp
+In a \%pipe%\ transport, when passing the message
+to a scanner program or
+to some other delivery mechanism such as UUCP, multiple recipients may be
+acceptable.
+.endp
+The three local transports (\%appendfile%\, \%lmtp%\, and \%pipe%\) all have
+the same options for controlling multiple (`batched') deliveries, namely
+\batch@_max\ and \batch@_id\. To save repeating the information for each
+transport, these options are described here.
+
+The \batch@_max\ option specifies the maximum number of addresses that can be
+delivered together in a single run of the transport. Its default value is one.
+When more than one address is routed to a transport that has a \batch@_max\
+value greater than one, the addresses are delivered in a batch (that is, in a
+single run of the transport), subject to certain conditions:
+.numberpars $.
+If any of the transport's options contain a reference to \$local@_part$\, no
+batching is possible.
+.nextp
+If any of the transport's options contain a reference to \$domain$\, only
+addresses with the same domain are batched.
+.nextp
+.index customizing||batching condition
+If \batch@_id\ is set, it is expanded for each address, and only those
+addresses with the same expanded value are batched. This allows you to specify
+customized batching conditions.
+Failure of the expansion for any reason, including forced failure, disables
+batching, but it does not stop the delivery from taking place.
+.nextp
+Batched addresses must also have the same errors address (where to send
+delivery errors), the same header additions and removals, the same user and
+group for the transport, and if a host list is present, the first host must
+be the same.
+.endp
+.index ::Envelope-to:: header line
+If the generic \envelope@_to@_add\ option is set for the transport, the
+::Envelope-to:: header that is added to the message contains all the addresses
+that are batched together.
+
+The \%appendfile%\ and \%pipe%\ transports have an option called \use@_bsmtp\,
+which causes them to deliver the message in `batched SMTP' format, with the
+envelope represented as SMTP commands. The \check@_string\ and \escape@_string\
+options are forced to the values
+.display asis
+check_string = "."
+escape_string = ".."
+.endd
+when batched SMTP is in use. A full description of the batch SMTP mechanism is
+given in section ~~SECTbatchSMTP. The \%lmtp%\ transport does not have a
+\use@_bsmtp\ option, because it always delivers using the SMTP protocol.
+
+.index \%pipe%\ transport||with multiple addresses
+If you are not using BSMTP, but are using a \%pipe%\ transport, you can include
+\$pipe@_addresses$\ as part of the command. This is not a true variable; it is
+a bit of magic that causes each of the recipient addresses to be inserted into
+the command as a separate argument. This provides a way of accessing all the
+addresses that are being delivered in the batch.
+
+If you are using a batching \%appendfile%\ transport without \use@_bsmtp\, the
+only way to preserve the recipient addresses is to set the \envelope@_to@_add\
+option. This causes an ::Envelope-to:: header line to be added to the message,
+containing all the recipients.
+
+
+
+.
+.
+.
+. ============================================================================
+.chapter The appendfile transport
+.set runningfoot "appendfile transport"
+.rset CHAPappendfile ~~chapter
+.index \%appendfile%\ transport
+.index transports||\%appendfile%\
+.index directory creation
+.index creating directories
+The \%appendfile%\ transport delivers a message by appending it to an existing
+file, or by creating an entirely new file in a specified directory. Single
+files to which messages are appended can be in the traditional Unix mailbox
+format, or optionally in the MBX format supported by the Pine MUA and
+University of Washington IMAP daemon, $it{inter alia}. When each message is
+being delivered as a separate file, `maildir' format can optionally be used to
+give added protection against failures that happen part-way through the
+delivery. A third form of separate-file delivery known as `mailstore' is also
+supported. For all file formats, Exim attempts to create as many levels of
+directory as necessary, provided that \create@_directory\ is set.
+
+The code for the optional formats is not included in the Exim binary by
+default. It is necessary to set \\SUPPORT@_MBX\\, \\SUPPORT@_MAILDIR\\ and/or
+\\SUPPORT@_MAILSTORE\\ in \(Local/Makefile)\ to have the appropriate code
+included.
+
+.index quota||system
+Exim recognises system quota errors, and generates an appropriate message. Exim
+also supports its own quota control within the transport, for use when the
+system facility is unavailable or cannot be used for some reason.
+
+If there is an error while appending to a file (for example, quota exceeded or
+partition filled), Exim attempts to reset the file's length and last
+modification time back to what they were before. If there is an error while
+creating an entirely new file, the new file is removed.
+
+Before appending to a file, a number of security checks are made, and the
+file is locked. A detailed description is given below, after the list of
+private options.
+
+\%appendfile%\ is most commonly used for local deliveries to users' mailboxes.
+However, it can also be used as a pseudo-remote transport for putting messages
+into files for remote delivery by some means other than Exim. `Batch SMTP'
+format is often used in this case (see the \use@_bsmtp\ option).
+
+
+.section The file and directory options
+.rset SECTfildiropt "~~chapter.~~section"
+The \file\ option specifies a single file, to which the message is appended;
+the \directory\ option specifies a directory, in which a new file containing
+the message is created. Only one of these two options can be set, and for
+normal deliveries to mailboxes, one of them \*must*\ be set.
+
+However, \%appendfile%\ is also used for delivering messages to files or
+directories whose names (or parts of names) are obtained from alias,
+forwarding, or filtering operations (for example, a \save\ command in a user's
+Exim filter). When such a transport is running, \$local@_part$\ contains the
+local part that was aliased or forwarded, and \$address@_file$\ contains the
+name (or partial name) of the file or directory generated by the redirection
+operation. There are two cases:
+.numberpars $.
+If neither \file\ nor \directory\ is set, the redirection operation
+must specify an absolute path (one that begins with \"/"\). This is the most
+common case when users with local accounts use filtering to sort mail into
+different folders. See for example, the \%address@_file%\ transport in the
+default configuration. If the path ends with a slash, it is assumed to be the
+name of a directory. A delivery to a directory can also be forced by setting
+\maildir@_format\ or \mailstore@_format\.
+.nextp
+If \file\ or \directory\ is set for a delivery from a redirection, it is used
+to determine the file or directory name for the delivery. Normally, the
+contents of \$address@_file$\ are used in some way in the string expansion.
+.endp
+
+.index Sieve filter||configuring \%appendfile%\
+.index Sieve filter||relative mailbox path handling
+As an example of the second case, consider an environment where users do not
+have home directories. They may be permitted to use Exim filter commands of the
+form:
+.display asis
+save folder23
+.endd
+or Sieve filter commands of the form:
+.display asis
+require "fileinto";
+fileinto "folder23";
+.endd
+In this situation, the expansion of \file\ or \directory\ in the transport must
+transform the relative path into an appropriate absolute file name. In the case
+of Sieve filters, the name \*inbox*\ must be handled. It is the name that is
+used as a result of a `keep' action in the filter. This example shows one way
+of handling this requirement:
+.display asis
+file = ${if eq{$address_file}{inbox} \
+ {/var/mail/$local_part} \
+ {${if eq{${substr_0_1:$address_file}}{/} \
+ {$address_file} \
+ {$home/mail/$address_file} \
+ }} \
+ }
+.endd
+With this setting of \file\, \*inbox*\ refers to the standard mailbox location,
+absolute paths are used without change, and other folders are in the \(mail)\
+directory within the home directory.
+
+\**Note 1**\: While processing an Exim filter, a relative path such as
+\(folder23)\ is turned into an absolute path if a home directory is known to
+the router. In particular, this is the case if \check@_local@_user\ is set. If
+you want to prevent this happening at routing time, you can set
+\router@_home@_directory\ empty. This forces the router to pass the relative
+path to the transport.
+
+\**Note 2**\: An absolute path in \$address@_file$\ is not treated specially;
+the \file\ or \directory\ option is still used if it is set.
+
+
+
+.section Private options for appendfile
+.index options||\%appendfile%\ transport
+
+.startconf
+
+.conf allow@_fifo boolean false
+.index fifo (named pipe)
+.index named pipe (fifo)
+.index pipe||named (fifo)
+Setting this option permits delivery to named pipes (FIFOs) as well as to
+regular files. If no process is reading the named pipe at delivery time, the
+delivery is deferred.
+
+.conf allow@_symlink boolean false
+.index symbolic link||to mailbox
+.index mailbox||symbolic link
+By default, \%appendfile%\ will not deliver if the path name for the file is
+that of a symbolic link. Setting this option relaxes that constraint, but there
+are security issues involved in the use of symbolic links. Be sure you know
+what you are doing if you set this. Details of exactly what this option affects
+are included in the discussion which follows this list of options.
+
+.conf batch@_id string$**$ unset
+See the description of local delivery batching in chapter ~~CHAPbatching.
+However, batching is automatically disabled for \%appendfile%\ deliveries that
+happen as a result of forwarding or aliasing or other redirection directly to a
+file.
+
+.conf batch@_max integer 1
+See the description of local delivery batching in chapter ~~CHAPbatching.
+
+.conf check@_group boolean false
+When this option is set, the group owner of the file defined by the \file\
+option is checked to see that it is the same as the group under which the
+delivery process is running. The default setting is false because the default
+file mode is 0600, which means that the group is irrelevant.
+
+.conf check@_owner boolean true
+When this option is set, the owner of the file defined by the \file\ option is
+checked to ensure that it is the same as the user under which the delivery
+process is running.
+
+.conf check@_string string "see below"
+.index `From' line
+As \%appendfile%\ writes the message, the start of each line is tested for
+matching \check@_string\, and if it does, the initial matching characters are
+replaced by the contents of \escape@_string\. The value of \check@_string\ is a
+literal string, not a regular expression, and the case of any letters it
+contains is significant.
+
+If \use@_bsmtp\ is set the values of \check@_string\ and \escape@_string\ are
+forced to `.' and `..' respectively, and any settings in the configuration are
+ignored. Otherwise, they default to `From ' and `>From ' when the \file\ option
+is set, and unset when
+any of the \directory\, \maildir\, or \mailstore\ options are set.
+
+The default settings, along with \message@_prefix\ and \message@_suffix\, are
+suitable for traditional `BSD' mailboxes, where a line beginning with `From '
+indicates the start of a new message. All four options need changing if another
+format is used. For example, to deliver to mailboxes in MMDF format:
+.index MMDF format mailbox
+.index mailbox||MMDF format
+.display asis
+check_string = "\1\1\1\1\n"
+escape_string = "\1\1\1\1 \n"
+message_prefix = "\1\1\1\1\n"
+message_suffix = "\1\1\1\1\n"
+.endd
+
+.index directory creation
+.conf create@_directory boolean true
+When this option is true, Exim attempts to create any missing superior
+directories for the file that it is about to write. A created directory's mode
+is given by the \directory@_mode\ option.
+
+.conf create@_file string "anywhere"
+This option constrains the location of files and directories that are created
+by this transport. It applies to files defined by the \file\ option and
+directories defined by the \directory\ option. In the case of maildir delivery,
+it applies to the top level directory, not the maildir directories beneath.
+
+The option must be set to one of the words `anywhere', `inhome', or
+`belowhome'. In the second and third cases, a home directory must have been set
+for the transport. This option is not useful when an explicit file name is
+given for normal mailbox deliveries. It is intended for the case when file
+names are generated from users' \(.forward)\ files. These are usually handled
+by an \%appendfile%\ transport called \address@_file\. See also
+\file@_must@_exist\.
+
+.conf directory string$**$ unset
+This option is mutually exclusive with the \file\ option, but one of \file\ or
+\directory\ must be set, unless the delivery is the direct result of a
+redirection (see section ~~SECTfildiropt).
+
+When \directory\ is set, the string is expanded, and the message is delivered
+into a new file or files in or below the given directory, instead of being
+appended to a single mailbox file. A number of different formats are provided
+(see \maildir@_format\ and \mailstore@_format\), and see section ~~SECTopdir
+for further details of this form of delivery.
+
+.conf directory@_file string$**$ "$tt{q@$@{base62:@$tod@_epoch@}-@$inode}"
+.index base62
+When \directory\ is set, but neither \maildir@_format\ nor \mailstore@_format\
+is set, \%appendfile%\ delivers each message into a file whose name is obtained
+by expanding this string. The default value generates a unique name from the
+current time, in base 62 form, and the inode of the file. The variable
+\$inode$\ is available only when expanding this option.
+
+.conf directory@_mode "octal integer" 0700
+If \%appendfile%\ creates any directories as a result of the \create@_directory\
+option, their mode is specified by this option.
+
+.conf escape@_string string "see description"
+See \check@_string\ above.
+
+.conf file string$**$ unset
+This option is mutually exclusive with the \directory\ option, but one of
+\file\ or \directory\ must be set, unless the delivery is the direct result of
+a redirection (see section ~~SECTfildiropt). The \file\ option specifies a
+single file, to which the message is appended. One or more of
+\use@_fcntl@_lock\, \use@_flock@_lock\, or \use@_lockfile\ must be set with
+\file\.
+.index NFS||lock file
+.index locking files
+.index lock files
+If you are using more than one host to deliver over NFS into the same
+mailboxes, you should always use lock files.
+
+The string value is expanded for each delivery, and must yield an absolute
+path. The most common settings of this option are variations on one of these
+examples:
+.display asis
+file = /var/spool/mail/$local_part
+file = /home/$local_part/inbox
+file = $home/inbox
+.endd
+.index `sticky' bit
+In the first example, all deliveries are done into the same directory. If Exim
+is configured to use lock files (see \use@_lockfile\ below) it must be able to
+create a file in the directory, so the `sticky' bit must be turned on for
+deliveries to be possible, or alternatively the \group\ option can be used to
+run the delivery under a group id which has write access to the directory.
+
+
+.conf file@_format string unset
+.index file||mailbox, checking existing format
+This option requests the transport to check the format of an existing file
+before adding to it. The check consists of matching a specific string at the
+start of the file. The value of the option consists of an even number of
+colon-separated strings. The first of each pair is the test string, and the
+second is the name of a transport. If the transport associated with a matched
+string is not the current transport, control is passed over to the other
+transport. For example, suppose the standard \%local@_delivery%\ transport has
+this added to it:
+.display asis
+file_format = "From : local_delivery :\
+ \1\1\1\1\n : local_mmdf_delivery"
+.endd
+Mailboxes that begin with `From' are still handled by this transport, but if a
+mailbox begins with four binary ones followed by a newline, control is passed
+to a transport called \local__mmdf__delivery\, which presumably is configured
+to do the delivery in MMDF format. If a mailbox does not exist or is empty, it
+is assumed to match the current transport. If the start of a mailbox doesn't
+match any string, or if the transport named for a given string is not defined,
+delivery is deferred.
+
+.conf file@_must@_exist boolean false
+If this option is true, the file specified by the \file\ option must exist, and
+an error occurs if it does not. Otherwise, it is created if it does not exist.
+
+.conf lock@_fcntl@_timeout time 0s
+.index timeout||mailbox locking
+.index mailbox locking||blocking and non-blocking
+.index locking files
+By default, the \%appendfile%\ transport uses non-blocking calls to \*fcntl()*\
+when locking an open mailbox file. If the call fails, the delivery process
+sleeps for \lock@_interval\ and tries again, up to \lock@_retries\ times.
+Non-blocking calls are used so that the file is not kept open during the wait
+for the lock; the reason for this is to make it as safe as possible for
+deliveries over NFS in the case when processes might be accessing an NFS
+mailbox without using a lock file. This should not be done, but
+misunderstandings and hence misconfigurations are not unknown.
+
+On a busy system, however, the performance of a non-blocking lock approach is
+not as good as using a blocking lock with a timeout. In this case, the waiting
+is done inside the system call, and Exim's delivery process acquires the lock
+and can proceed as soon as the previous lock holder releases it.
+
+If \lock@_fcntl@_timeout\ is set to a non-zero time, blocking locks, with that
+timeout, are used. There may still be some retrying: the maximum number of
+retries is
+.display asis
+(lock_retries * lock_interval) / lock_fcntl_timeout
+.endd
+rounded up to the next whole number. In other words, the total time during
+which \%appendfile%\ is trying to get a lock is roughly the same, unless
+\lock@_fcntl@_timeout\ is set very large.
+
+You should consider setting this option if you are getting a lot of delayed
+local deliveries because of errors of the form
+.display asis
+failed to lock mailbox /some/file (fcntl)
+.endd
+
+.conf lock@_flock@_timeout time 0s
+This timeout applies to file locking when using \*flock()*\ (see \use@_flock\);
+the timeout operates in a similar manner to \lock@_fcntl@_timeout\.
+
+.conf lock@_interval time 3s
+This specifies the time to wait between attempts to lock the file. See below
+for details of locking.
+
+.conf lock@_retries integer 10
+This specifies the maximum number of attempts to lock the file. A value of zero
+is treated as 1. See below for details of locking.
+
+.conf lockfile@_mode "octal integer" 0600
+This specifies the mode of the created lock file, when a lock file is being
+used (see \use@_lockfile\).
+
+.conf lockfile@_timeout time 30m
+.index timeout||mailbox locking
+When a lock file is being used (see \use@_lockfile\), if a lock file already
+exists and is older than this value, it is assumed to have been left behind by
+accident, and Exim attempts to remove it.
+
+.conf maildir@_format boolean false
+.index maildir format||specifying
+If this option is set with the \directory\ option, the delivery is into a new
+file, in the `maildir' format that is used by other mail software. When the
+transport is activated directly from a \%redirect%\ router (for example, the
+\%address@_file%\ transport in the default configuration), setting
+\maildir@_format\ causes the path received from the router to be treated as a
+directory, whether or not it ends with \"/"\. This option is available only if
+\\SUPPORT@_MAILDIR\\ is present in \(Local/Makefile)\. See section
+~~SECTmaildirdelivery below for further details.
+
+.em
+.conf maildir@_quota@_directory@_regex string "See below"
+.index maildir format||quota, directories included in
+.index quota||maildir, directories included in
+This option is relevant only when \maildir@_use@_size@_file\ is set. It defines
+a regular expression for specifying directories that should be included in the
+quota calculation. The default value is
+.display asis
+maildir_quota_directory_regex = ^(?:cur|new|\..*)$
+.endd
+which includes the \(cur)\ and \(new)\ directories, and any maildir++ folders
+(directories whose names begin with a dot). If you want to exclude the
+\(Trash)\
+folder from the count (as some sites do), you need to change this setting to
+.display asis
+maildir_quota_directory_regex = ^(?:cur|new|\.(?!Trash).*)$
+.endd
+This uses a negative lookahead in the regular expression to exclude the
+directory whose name is \(.Trash)\.
+.nem
+
+.conf maildir@_retries integer 10
+This option specifies the number of times to retry when writing a file in
+`maildir' format. See section ~~SECTmaildirdelivery below.
+
+.conf maildir@_tag string$**$ unset
+This option applies only to deliveries in maildir format, and is described in
+section ~~SECTmaildirdelivery below.
+
+.conf maildir@_use@_size@_file boolean false
+.index maildir format||\(maildirsize)\ file
+Setting this option true enables support for \(maildirsize)\ files. Exim
+creates a \(maildirsize)\ file in a maildir if one does not exist, taking the
+quota from the \quota\ option of the transport. If \quota\ is unset, the value
+is zero. See section ~~SECTmaildirdelivery below for further details.
+
+.conf mailstore@_format boolean false
+.index mailstore format||specifying
+If this option is set with the \directory\ option, the delivery is into two new
+files in `mailstore' format. The option is available only if
+\\SUPPORT@_MAILSTORE\\ is present in \(Local/Makefile)\. See section
+~~SECTopdir below for further details.
+
+.conf mailstore@_prefix string$**$ unset
+This option applies only to deliveries in mailstore format, and is described in
+section ~~SECTopdir below.
+
+.conf mailstore@_suffix string$**$ unset
+This option applies only to deliveries in mailstore format, and is described in
+section ~~SECTopdir below.
+
+.conf mbx@_format boolean false
+.index locking files
+.index file||locking
+.index file||MBX format
+.index MBX format, specifying
+This option is available only if Exim has been compiled with \\SUPPORT@_MBX\\
+set in \(Local/Makefile)\. If \mbx@_format\ is set with the \file\ option,
+the message is appended to the mailbox file in MBX format instead of
+traditional Unix format. This format is supported by Pine4 and its associated
+IMAP and POP daemons, by means of the \*c-client*\ library that they all use.
+
+\**Note**\: The \message@_prefix\ and \message@_suffix\ options are not
+automatically changed by the use of \mbx@_format\. They should normally be set
+empty when using MBX format, so this option almost always appears in this
+combination:
+.display asis
+mbx_format = true
+message_prefix =
+message_suffix =
+.endd
+
+If none of the locking options are mentioned in the configuration,
+\use@_mbx@_lock\ is assumed and the other locking options default to false. It
+is possible to specify the other kinds of locking with \mbx@_format\, but
+\use@_fcntl@_lock\ and \use@_mbx@_lock\ are mutually exclusive. MBX locking
+interworks with \*c-client*\, providing for shared access to the mailbox. It
+should not be used if any program that does not use this form of locking is
+going to access the mailbox, nor should it be used if the mailbox file is NFS
+mounted, because it works only when the mailbox is accessed from a single host.
+
+If you set \use@_fcntl@_lock\ with an MBX-format mailbox, you cannot use
+the standard version of \*c-client*\, because as long as it has a mailbox open
+(this means for the whole of a Pine or IMAP session), Exim will not be able to
+append messages to it.
+
+.conf message@_prefix string$**$ "see below"
+.index `From' line
+The string specified here is expanded and output at the start of every message.
+The default is unset unless \file\ is specified and \use@_bsmtp\ is not set, in
+which case it is:
+.display asis
+message_prefix = "From ${if def:return_path{$return_path}\
+ {MAILER-DAEMON}} $tod_bsdinbox\n"
+.endd
+
+.conf message@_suffix string$**$ "see below"
+The string specified here is expanded and output at the end of every message.
+The default is unset unless \file\ is specified and \use@_bsmtp\ is not set, in
+which case it is a single newline character. The suffix can be suppressed by
+setting
+.display asis
+message_suffix =
+.endd
+
+.conf mode "octal integer" 0600
+If the output file is created, it is given this mode. If it already exists and
+has wider permissions, they are reduced to this mode. If it has narrower
+permissions, an error occurs unless \mode__fail__narrower\ is false. However,
+if the delivery is the result of a \save\ command in a filter file specifing a
+particular mode, the mode of the output file is always forced to take that
+value, and this option is ignored.
+
+.conf mode@_fail@_narrower boolean true
+This option applies in the case when an existing mailbox file has a narrower
+mode than that specified by the \mode\ option. If \mode@_fail@_narrower\ is
+true, the delivery is deferred (`mailbox has the wrong mode'); otherwise Exim
+continues with the delivery attempt, using the existing mode of the file.
+
+.conf notify@_comsat boolean false
+If this option is true, the \*comsat*\ daemon is notified after every successful
+delivery to a user mailbox. This is the daemon that notifies logged on users
+about incoming mail.
+
+.conf quota string$**$ unset
+.index quota||imposed by Exim
+This option imposes a limit on the size of the file to which Exim is appending,
+or to the total space used in the directory tree when the \directory\ option is
+set. In the latter case, computation of the space used is expensive, because
+all the files in the directory (and any sub-directories) have to be
+individually inspected and their sizes summed.
+.em
+(See \quota@_size@_regex\ and \maildir@_use@_size@_file\ for ways to avoid this
+in environments where users have no shell access to their mailboxes).
+
+As there is no interlock against two simultaneous deliveries into a
+multi-file mailbox, it is possible for the quota to be overrun in this case.
+For single-file mailboxes, of course, an interlock is a necessity.
+.nem
+
+A file's size is taken as its \*used*\ value. Because of blocking effects, this
+may be a lot less than the actual amount of disk space allocated to the file.
+If the sizes of a number of files are being added up, the rounding effect can
+become quite noticeable, especially on systems that have large block sizes.
+Nevertheless, it seems best to stick to the \*used*\ figure, because this is
+the obvious value which users understand most easily.
+
+The value of the option is expanded, and must then be a numerical value
+(decimal point allowed), optionally followed by one of the letters K or M. The
+expansion happens while Exim is running as root, before it changes uid for the
+delivery. This means that files which are inaccessible to the end user can be
+used to hold quota values that are looked up in the expansion. When delivery
+fails because this quota is exceeded, the handling of the error is as for
+system quota failures.
+
+.em
+\**Note**\: A value of zero is interpreted as `no quota'.
+.nem
+
+By default, Exim's quota checking mimics system quotas, and restricts the
+mailbox to the specified maximum size, though the value is not accurate to the
+last byte, owing to separator lines and additional headers that may get added
+during message delivery. When a mailbox is nearly full, large messages may get
+refused even though small ones are accepted, because the size of the current
+message is added to the quota when the check is made. This behaviour can be
+changed by setting \quota@_is@_inclusive\ false. When this is done, the check
+for exceeding the quota does not include the current message. Thus, deliveries
+continue until the quota has been exceeded; thereafter, no further messages are
+delivered. See also \quota@_warn@_threshold\.
+
+.conf quota@_directory string$**$ unset
+This option defines the directory to check for quota purposes when delivering
+into individual files. The default is the delivery directory, or, if a file
+called \(maildirfolder)\ exists in a maildir directory, the parent of the
+delivery directory.
+
+.conf quota@_filecount string$**$ 0
+This option applies when the \directory\ option is set. It limits the total
+number of files in the directory (compare the inode limit in system quotas). It
+can only be used if \quota\ is also set. The value is expanded; an expansion
+failure causes delivery to be deferred.
+
+.conf quota@_is@_inclusive boolean true
+See \quota\ above.
+
+.conf quota@_size@_regex string unset
+This option applies when one of the delivery modes that writes a separate file
+for each message is being used. When Exim wants to find the size of one of
+these files in order to test the quota, it first checks \quota@_size@_regex\.
+If this is set to a regular expression that matches the file name, and it
+captures one string, that string is interpreted as a representation of the
+file's size. The value of \quota@_size@_regex\ is not expanded.
+
+This feature is useful only when users have no shell access to their mailboxes
+-- otherwise they could defeat the quota simply by renaming the files. This
+facility can be used with maildir deliveries, by setting \maildir@_tag\ to add
+the file length to the file name. For example:
+.display asis
+maildir_tag = ,S=$message_size
+quota_size_regex = ,S=(\d+)
+.endd
+The regular expression should not assume that the length is at the end of the
+file name (even though \maildir@_tag\ puts it there) because maildir MUAs
+sometimes add other information onto the ends of message file names.
+
+.conf quota@_warn@_message string$**$ "see below"
+See below for the use of this option. If it is not set when
+\quota@_warn@_threshold\ is set, it defaults to
+.display asis
+quota_warn_message = "\
+ To: $local_part@$domain\n\
+ Subject: Your mailbox\n\n\
+ This message is automatically created \
+ by mail delivery software.\n\n\
+ The size of your mailbox has exceeded \
+ a warning threshold that is\n\
+ set by the system administrator.\n"
+.endd
+
+.conf quota@_warn@_threshold string$**$ 0
+.index quota||warning threshold
+.index mailbox||size warning
+.index size||of mailbox
+This option is expanded in the same way as \quota\ (see above). If the
+resulting value is greater than zero, and delivery of the message causes the
+size of the file or total space in the directory tree to cross the given
+threshold, a warning message is sent. If \quota\ is also set, the threshold may
+be specified as a percentage of it by following the value with a percent sign.
+For example:
+.display asis
+quota = 10M
+quota_warn_threshold = 75%
+.endd
+If \quota\ is not set, a setting of \quota@_warn@_threshold\ that ends with a
+percent sign is ignored.
+
+The warning message itself is specified by the \quota@_warn@_message\ option,
+and it must start with a ::To:: header line containing the recipient(s). A
+::Subject:: line should also normally be supplied. The \quota\ option does not
+have to be set in order to use this option; they are independent of one
+another except when the threshold is specified as a percentage.
+
+.conf use@_bsmtp boolean false
+.index envelope sender
+If this option is set true, \%appendfile%\ writes messages in `batch SMTP'
+format, with the envelope sender and recipient(s) included as SMTP commands. If
+you want to include a leading \\HELO\\ command with such messages, you can do
+so by setting the \message@_prefix\ option. See section ~~SECTbatchSMTP for
+details of batch SMTP.
+
+.conf use@_crlf boolean false
+.index carriage return
+.index linefeed
+This option causes lines to be terminated with the two-character CRLF sequence
+(carriage return, linefeed) instead of just a linefeed character. In the case
+of batched SMTP, the byte sequence written to the file is then an exact image
+of what would be sent down a real SMTP connection.
+
+The contents of the \message@_prefix\ and \message@_suffix\ options are written
+verbatim, so must contain their own carriage return characters if these are
+needed. In cases where these options have non-empty defaults, the values end
+with a single linefeed, so they
+must
+be changed to end with \"@\r@\n"\ if \use@_crlf\ is set.
+
+.conf use@_fcntl@_lock boolean "see below"
+This option controls the use of the \*fcntl()*\ function to lock a file for
+exclusive use when a message is being appended. It is set by default unless
+\use@_flock@_lock\ is set. Otherwise, it should be turned off only if you know
+that all your MUAs use lock file locking. When both \use@_fcntl@_lock\ and
+\use@_flock@_lock\ are unset, \use@_lockfile\ must be set.
+
+.conf use@_flock@_lock boolean false
+This option is provided to support the use of \*flock()*\ for file locking, for
+the few situations where it is needed. Most modern operating systems support
+\*fcntl()*\ and \*lockf()*\ locking, and these two functions interwork with
+each other. Exim uses \*fcntl()*\ locking by default.
+
+This option is required only if you are using an operating system where
+\*flock()*\ is used by programs that access mailboxes (typically MUAs), and
+where \*flock()*\ does not correctly interwork with \*fcntl()*\. You can use
+both \*fcntl()*\ and \*flock()*\ locking simultaneously if you want.
+
+.index Solaris||\*flock()*\ support
+Not all operating systems provide \*flock()*\. Some versions of Solaris do not
+have it (and some, I think, provide a not quite right version built on top of
+\*lockf()*\). If the OS does not have \*flock()*\, Exim will be built without
+the ability to use it, and any attempt to do so will cause a configuration
+error.
+
+\**Warning**\: \*flock()*\ locks do not work on NFS files (unless \*flock()*\
+is just being mapped onto \*fcntl()*\ by the OS).
+
+.conf use@_lockfile boolean "see below"
+If this option is turned off, Exim does not attempt to create a lock file when
+appending to a mailbox file. In this situation, the only locking is by
+\*fcntl()*\. You should only turn \use@_lockfile\ off if you are absolutely
+sure that every MUA that is ever going to look at your users' mailboxes uses
+\*fcntl()*\ rather than a lock file, and even then only when you are not
+delivering over NFS from more than one host.
+
+.index NFS||lock file
+In order to append to an NFS file safely from more than one host, it is
+necessary to take out a lock $it{before} opening the file, and the lock file
+achieves this. Otherwise, even with \*fcntl()*\ locking, there is a risk of
+file corruption.
+
+The \use@_lockfile\ option is set by default unless \use@_mbx@_lock\ is set. It
+is not possible to turn both \use@_lockfile\ and \use@_fcntl@_lock\ off, except
+when \mbx@_format\ is set.
+
+.conf use@_mbx@_lock boolean "see below"
+This option is available only if Exim has been compiled with \\SUPPORT@_MBX\\
+set in \(Local/Makefile)\. Setting the option specifies that special MBX
+locking rules be used. It is set by default if \mbx@_format\ is set and none of
+the locking options are mentioned in the configuration. The locking rules are
+the same as are used by the \*c-client*\ library that underlies Pine and the
+IMAP4 and POP daemons that come with it (see the discussion below). The rules
+allow for shared access to the mailbox. However, this kind of locking does not
+work when the mailbox is NFS mounted.
+
+You can set \use@_mbx@_lock\ with either (or both) of \use@_fcntl@_lock\ and
+\use@_flock@_lock\ to control what kind of locking is used in implementing the
+MBX locking rules. The default is to use \*fcntl()*\ if \use@_mbx@_lock\ is set
+without \use@_fcntl@_lock\ or \use@_flock@_lock\.
+.endconf
+
+
+.section Operational details for appending
+.rset SECTopappend "~~chapter.~~section"
+.index appending to a file
+.index file||appending
+Before appending to a file, the following preparations are made:
+.numberpars $.
+If the name of the file is \(/dev/null)\, no action is taken, and a success
+return is given.
+.nextp
+.index directory creation
+If any directories on the file's path are missing, Exim creates them if the
+\create@_directory\ option is set. A created directory's mode is given by the
+\directory@_mode\ option.
+.nextp
+If \file@_format\ is set, the format of an existing file is checked. If this
+indicates that a different transport should be used, control is passed to that
+transport.
+.nextp
+.index file||locking
+.index locking files
+.index NFS||lock file
+If \use@_lockfile\ is set, a lock file is built in a way that will work
+reliably over NFS, as follows:
+.numberpars $.
+Create a `hitching post' file whose name is that of the lock file with the
+current time, primary host name, and process id added, by opening for writing
+as a new file. If this fails with an access error, delivery is deferred.
+.nextp
+Close the hitching post file, and hard link it to the lock file name.
+.nextp
+If the call to \*link()*\ succeeds, creation of the lock file has succeeded.
+Unlink the hitching post name.
+.nextp
+Otherwise, use \*stat()*\ to get information about the hitching post file, and
+then unlink hitching post name. If the number of links is exactly two, creation
+of the lock file succeeded but something (for example, an NFS server crash and
+restart) caused this fact not to be communicated to the \*link()*\ call.
+.nextp
+If creation of the lock file failed, wait for \lock@_interval\ and try again,
+up to \lock@_retries\ times. However, since any program that writes to a
+mailbox should complete its task very quickly, it is reasonable to time out old
+lock files that are normally the result of user agent and system crashes. If an
+existing lock file is older than \lockfile@_timeout\ Exim attempts to unlink it
+before trying again.
+.endp
+.nextp
+A call is made to \*lstat()*\ to discover whether the main file exists, and if
+so, what its characteristics are. If \*lstat()*\ fails for any reason other
+than non-existence, delivery is deferred.
+.nextp
+.index symbolic link||to mailbox
+.index mailbox||symbolic link
+If the file does exist and is a symbolic link, delivery is deferred, unless the
+\allow@_symlink\ option is set, in which case the ownership of the link is
+checked, and then \*stat()*\ is called to find out about the real file, which
+is then subjected to the checks below. The check on the top-level link
+ownership prevents one user creating a link for another's mailbox in a sticky
+directory, though allowing symbolic links in this case is definitely not a good
+idea. If there is a chain of symbolic links, the intermediate ones are not
+checked.
+.nextp
+If the file already exists but is not a regular file, or if the file's owner
+and group (if the group is being checked -- see \check@_group\ above) are
+different from the user and group under which the delivery is running,
+delivery is deferred.
+.nextp
+If the file's permissions are more generous than specified, they are reduced.
+If they are insufficient, delivery is deferred, unless \mode@_fail@_narrower\
+is set false, in which case the delivery is tried using the existing
+permissions.
+.nextp
+The file's inode number is saved, and the file is then opened for appending. If
+this fails because the file has vanished, \%appendfile%\ behaves as if it hadn't
+existed (see below). For any other failures, delivery is deferred.
+.nextp
+If the file is opened successfully, check that the inode number hasn't
+changed, that it is still a regular file, and that the owner and permissions
+have not changed. If anything is wrong, defer delivery and freeze the message.
+.nextp
+If the file did not exist originally, defer delivery if the \file@_must@_exist\
+option is set. Otherwise, check that the file is being created in a permitted
+directory if the \create@_file\ option is set (deferring on failure), and then
+open for writing as a new file, with the \\O@_EXCL\\ and \\O@_CREAT\\ options,
+except when dealing with a symbolic link (the \allow@_symlink\ option must be
+set). In this case, which can happen if the link points to a non-existent file,
+the file is opened for writing using \\O@_CREAT\\ but not \\O@_EXCL\\, because
+that prevents link following.
+.nextp
+.index loop||while file testing
+If opening fails because the file exists, obey the tests given above for
+existing files. However, to avoid looping in a situation where the file is
+being continuously created and destroyed, the exists/not-exists loop is broken
+after 10 repetitions, and the message is then frozen.
+.nextp
+If opening fails with any other error, defer delivery.
+.nextp
+.index file||locking
+.index locking files
+Once the file is open, unless both \use@_fcntl@_lock\ and \use@_flock@_lock\
+are false, it is locked using \*fcntl()*\ or \*flock()*\ or both. If
+\use@_mbx@_lock\ is false, an exclusive lock is requested in each case.
+However, if \use@_mbx@_lock\ is true,
+Exim takes out a shared lock on the open file,
+and an exclusive lock on the file whose name is
+.display
+/tmp/.<<device-number>>.<<inode-number>>
+.endd
+using the device and inode numbers of the open mailbox file, in accordance with
+the MBX locking rules.
+
+If Exim fails to lock the file, there are two possible courses of action,
+depending on the value of the locking timeout. This is obtained from
+\lock@_fcntl@_timeout\ or \lock@_flock@_timeout\, as appropriate.
+
+If the timeout value is zero, the file is closed, Exim waits for
+\lock@_interval\, and then goes back and re-opens the file as above and tries
+to lock it again. This happens up to \lock@_retries\ times, after which the
+delivery is deferred.
+
+If the timeout has a value greater than zero, blocking calls to \*fcntl()*\ or
+\*flock()*\ are used (with the given timeout), so there has already been some
+waiting involved by the time locking fails. Nevertheless, Exim does not give up
+immediately. It retries up to
+.display
+(lock@_retries * lock@_interval) / <<timeout>>
+.endd
+times (rounded up).
+.endp
+
+At the end of delivery, Exim closes the file (which releases the \*fcntl()*\
+and/or \*flock()*\ locks) and then deletes the lock file if one was created.
+
+.section Operational details for delivery to a new file
+.rset SECTopdir "~~chapter.~~section"
+.index delivery||to single file
+.index `From' line
+When the \directory\ option is set instead of \file\, each message is delivered
+into a newly-created file or set of files. When \%appendfile%\ is activated
+directly from a \%redirect%\ router, neither \file\ nor \directory\ is normally
+set, because the path for delivery is supplied by the router. (See for example,
+the \%address@_file%\ transport in the default configuration.) In this case,
+delivery is to a new file if either the path name ends in \"/"\, or the
+\maildir@_format\ or \mailstore@_format\ option is set.
+
+No locking is required while writing the message to a new file, so the various
+locking options of the transport are ignored. The `From' line that by default
+separates messages in a single file is not normally needed, nor is the escaping
+of message lines that start with `From', and there is no need to ensure a
+newline at the end of each message. Consequently, the default values for
+\check@_string\, \message@_prefix\, and \message@_suffix\ are all unset when
+any of \directory\, \maildir@_format\, or \mailstore@_format\ is set.
+
+If Exim is required to check a \quota\ setting, it adds up the sizes of all the
+files in the delivery directory by default. However, you can specify a
+different directory by setting \quota@_directory\. Also, for maildir deliveries
+(see below) the \(maildirfolder)\ convention is honoured.
+
+
+.index maildir format
+.index mailstore format
+There are three different ways in which delivery to individual files can be
+done, controlled by the settings of the \maildir@_format\ and
+\mailstore@_format\ options. Note that code to support maildir or mailstore
+formats is not included in the binary unless \\SUPPORT@_MAILDIR\\ or
+\\SUPPORT@_MAILSTORE\\, respectively, is set in \(Local/Makefile)\.
+
+.index directory creation
+In all three cases an attempt is made to create the directory and any necessary
+sub-directories if they do not exist, provided that the \create@_directory\
+option is set (the default). The location of a created directory can be
+constrained by setting \create@_file\. A created directory's mode is given by
+the \directory@_mode\ option. If creation fails, or if the \create@_directory\
+option is not set when creation is required, delivery is deferred.
+
+
+.section Maildir delivery
+.rset SECTmaildirdelivery "~~chapter.~~section"
+.index maildir format||description of
+If the \maildir@_format\ option is true, Exim delivers each message by writing
+it to a file whose name is \(tmp/<<stime>>.H<<mtime>>P<<pid>>.<<host>>)\ in the
+given directory. If the delivery is successful, the file is renamed into the
+\(new)\ subdirectory.
+
+In the file name, <<stime>> is the current time of day in seconds, and
+<<mtime>> is the microsecond fraction of the time. After a maildir delivery,
+Exim checks that the time-of-day clock has moved on by at least one microsecond
+before terminating the delivery process. This guarantees uniqueness for the
+file name. However, as a precaution, Exim calls \*stat()*\ for the file before
+opening it. If any response other than \\ENOENT\\ (does not exist) is given,
+Exim waits 2 seconds and tries again, up to \maildir@_retries\ times.
+
+.index quota||in maildir delivery
+.index maildir++
+If Exim is required to check a \quota\ setting before a maildir delivery, and
+\quota@_directory\ is not set, it looks for a file called \(maildirfolder)\ in
+the maildir directory (alongside \(new)\, \(cur)\, \(tmp)\). If this exists,
+Exim assumes the directory is a maildir++ folder directory, which is one level
+down from the user's top level mailbox directory. This causes it to start at
+the parent directory instead of the current directory when calculating the
+amount of space used.
+
+
+.section Using tags to record message sizes
+If \maildir@_tag\ is set, the string is expanded for each delivery.
+When the maildir file is renamed into the \(new)\ sub-directory, the
+tag is added to its name. However, if adding the tag takes the length of the
+name to the point where the test \*stat()*\ call fails with \\ENAMETOOLONG\\,
+the tag is dropped and the maildir file is created with no tag.
+
+Tags can be used to encode the size of files in their names; see
+\quota@_size@_regex\ above for an example. The expansion of \maildir@_tag\
+happens after the message has been written. The value of the \$message@_size$\
+variable is set to the number of bytes actually written. If the expansion is
+forced to fail, the tag is ignored, but a non-forced failure causes delivery to
+be deferred. The expanded tag may contain any printing characters except `/'.
+Non-printing characters in the string are ignored; if the resulting string is
+empty, it is ignored. If it starts with an alphanumeric character, a leading
+colon is inserted.
+
+
+.em
+.section Using a maildirsize file
+.index quota||in maildir delivery
+.index maildir format||\(maildirsize)\ file
+If \maildir@_use@_size@_file\ is true, Exim implements the maildir++ rules for
+storing quota and message size information in a file called \(maildirsize)\
+within the maildir directory. If this file does not exist, Exim creates it,
+setting the quota from the \quota\ option of the transport. If the maildir
+directory itself does not exist, it is created before any attempt to write a
+\(maildirsize)\ file.
+
+The \(maildirsize)\ file is used to hold information about the sizes of
+messages in the maildir, thus speeding up quota calculations. The quota value
+in the file is just a cache; if the quota is changed in the transport, the new
+value overrides the cached value when the next message is delivered. The cache
+is maintained for the benefit of other programs that access the maildir and
+need to know the quota.
+
+If the \quota\ option in the transport is unset or zero, the \(maildirsize)\
+file is maintained (with a zero quota setting), but no quota is imposed.
+
+A regular expression is available for controlling which directories in the
+maildir participate in quota calculations. See the description of the
+\maildir@_quota@_directory@_regex\ option above for details.
+.nem
+
+
+.section Mailstore delivery
+.index mailstore format||description of
+If the \mailstore@_format\ option is true, each message is written as two files
+in the given directory. A unique base name is constructed from the message id
+and the current delivery process, and the files that are written use this base
+name plus the suffixes \(.env)\ and \(.msg)\. The \(.env)\ file contains the
+message's envelope, and the \(.msg)\ file contains the message itself.
+
+During delivery, the envelope is first written to a file with the suffix
+\(.tmp)\. The \(.msg)\ file is then written, and when it is complete, the
+\(.tmp)\ file is renamed as the \(.env)\ file. Programs that access messages in
+mailstore format should wait for the presence of both a \(.msg)\ and a \(.env)\
+file before accessing either of them. An alternative approach is to wait for
+the absence of a \(.tmp)\ file.
+
+The envelope file starts with any text defined by the \mailstore@_prefix\
+option, expanded and terminated by a newline if there isn't one. Then follows
+the sender address on one line, then all the recipient addresses, one per line.
+There can be more than one recipient only if the \batch@_max\ option is set
+greater than one. Finally, \mailstore@_suffix\ is expanded and the result
+appended to the file, followed by a newline if it does not end with one.
+
+If expansion of \mailstore@_prefix\ or \mailstore@_suffix\ ends with a forced
+failure, it is ignored. Other expansion errors are treated as serious
+configuration errors, and delivery is deferred.
+
+
+.section Non-special new file delivery
+If neither \maildir@_format\ nor \mailstore@_format\ is set, a single new file
+is created directly in the named directory. For example, when delivering
+messages into files in batched SMTP format for later delivery to some host (see
+section ~~SECTbatchSMTP), a setting such as
+.display asis
+directory = /var/bsmtp/$host
+.endd
+might be used. A message is written to a file with a temporary name, which is
+then renamed when the delivery is complete. The final name is obtained by
+expanding the contents of the \directory@_file\ option.
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The autoreply transport
+.set runningfoot "autoreply transport"
+.index transports||\%autoreply%\
+.index \%autoreply%\ transport
+The \%autoreply%\ transport is not a true transport in that it does not cause
+the message to be transmitted. Instead, it generates another mail message. It
+is usually run as the result of mail filtering, a `vacation' message being the
+standard example. However, it can also be run directly from a router like any
+other transport. To reduce the possibility of message cascades, messages
+created by the \%autoreply%\ transport always have empty envelope sender
+addresses, like bounce messages.
+
+The parameters of the message to be sent can be specified in the configuration
+by options described below. However, these are used only when the address
+passed to the transport does not contain its own reply information. When the
+transport is run as a consequence of a
+\mail\
+or \vacation\ command in a filter file, the parameters of the message are
+supplied by the filter, and passed with the address. The transport's options
+that define the message are then ignored (so they are not usually set in this
+case). The message is specified entirely by the filter or by the transport; it
+is never built from a mixture of options. However, the \file@_optional\,
+\mode\, and \return@_message\ options apply in all cases.
+
+\%Autoreply%\ is implemented as a local transport. When used as a result of a
+command in a user's filter file, \%autoreply%\ normally runs under the uid and
+gid of the user, and with appropriate current and home directories (see chapter
+~~CHAPenvironment).
+
+There is a subtle difference between routing a message to a \%pipe%\ transport
+that generates some text to be returned to the sender, and routing it to an
+\%autoreply%\ transport. This difference is noticeable only if more than one
+address from the same message is so handled. In the case of a pipe, the
+separate outputs from the different addresses are gathered up and returned to
+the sender in a single message, whereas if \%autoreply%\ is used, a separate
+message is generated for each address that is passed to it.
+
+Non-printing characters are not permitted in the header lines generated for the
+message that \%autoreply%\ creates, with the exception of newlines that are
+immediately followed by whitespace. If any non-printing characters are found,
+the transport defers.
+Whether characters with the top bit set count as printing characters or not is
+controlled by the \print@_topbitchars\ global option.
+
+If any of the generic options for manipulating headers (for example,
+\headers@_add\) are set on an \%autoreply%\ transport, they apply to the copy of
+the original message that is included in the generated message when
+\return@_message\ is set. They do not apply to the generated message itself.
+
+If the \%autoreply%\ transport receives return code 2 from Exim when it submits
+the message, indicating that there were no recipients, it does not treat this
+as an error. This means that autoreplies sent to \$sender@_address$\ when this
+is empty (because the incoming message is a bounce message) do not cause
+problems. They are just discarded.
+
+
+.section Private options for autoreply
+
+.startconf
+.index options||\%autoreply%\ transport
+.conf bcc string$**$ unset
+This specifies the addresses that are to receive `blind carbon copies' of the
+message when the message is specified by the transport.
+
+.conf cc string$**$ unset
+This specifies recipients of the message and the contents of the ::Cc:: header
+when the message is specified by the transport.
+
+.conf file string$**$ unset
+The contents of the file are sent as the body of the message when the message
+is specified by the transport. If both \file\ and \text\ are set, the text
+string comes first.
+
+.conf file@_expand boolean false
+If this is set, the contents of the file named by the \file\ option are
+subjected to string expansion as they are added to the message.
+
+.conf file@_optional boolean false
+If this option is true, no error is generated if the file named by the \file\
+option or passed with the address does not exist or cannot be read.
+
+.conf from string$**$ unset
+This specifies the contents of the ::From:: header when the message is specified
+by the transport.
+
+.conf headers string$**$ unset
+This specifies additional RFC 2822 headers that are to be added to the message when
+the message is specified by the transport. Several can be given by using `@\n'
+to separate them. There is no check on the format.
+
+.conf log string$**$ unset
+This option names a file in which a record of every message sent is logged when
+the message is specified by the transport.
+
+.conf mode "octal integer" 0600
+If either the log file or the `once' file has to be created, this mode is used.
+
+.conf once string$**$ unset
+This option names a file or DBM database in which a record of each
+::To:: recipient is kept when the message is specified by the transport.
+\**Note**\: This does not apply to ::Cc:: or ::Bcc:: recipients.
+If \once@_file@_size\ is not set, a DBM database is used, and it is allowed to
+grow as large as necessary. If a potential recipient is already in the
+database, no message is sent by default. However, if \once@_repeat\ specifies a
+time greater than zero, the message is sent if that much time has elapsed since
+a message was last sent to this recipient. If \once\ is unset, the message is
+always sent.
+
+If \once@_file@_size\ is set greater than zero, it changes the way Exim
+implements the \once\ option. Instead of using a DBM file to record every
+recipient it sends to, it uses a regular file, whose size will never get larger
+than the given value. In the file, it keeps a linear list of recipient
+addresses and times at which they were sent messages. If the file is full when
+a new address needs to be added, the oldest address is dropped. If
+\once@_repeat\ is not set, this means that a given recipient may receive
+multiple messages, but at unpredictable intervals that depend on the rate of
+turnover of addresses in the file. If \once@_repeat\ is set, it specifies a
+maximum time between repeats.
+
+.conf once@_file@_size integer 0
+See \once\ above.
+
+.conf once@_repeat time$**$ 0s
+See \once\ above.
+After expansion, the value of this option must be a valid time value.
+
+.conf reply@_to string$**$ unset
+This specifies the contents of the ::Reply-To:: header when the message is
+specified by the transport.
+
+.conf return@_message boolean false
+If this is set, a copy of the original message is returned with the new
+message, subject to the maximum size set in the \return@_size@_limit\ global
+configuration option.
+
+.conf subject string$**$ unset
+This specifies the contents of the ::Subject:: header when the message is
+specified by the transport.
+
+.conf text string$**$ unset
+This specifies a single string to be used as the body of the message when the
+message is specified by the transport. If both \text\ and \file\ are set, the
+text comes first.
+
+.conf to string$**$ unset
+This specifies recipients of the message and the contents of the ::To:: header
+when the message is specified by the transport.
+
+.endconf
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The lmtp transport
+.set runningfoot "lmtp transport"
+.index transports||\%lmtp%\
+.index \%lmtp%\ transport
+.index LMTP||over a pipe
+.index LMTP||over a socket
+.rset CHAPLMTP "~~chapter"
+The \%lmtp%\ transport runs the LMTP protocol (RFC 2033) over a pipe to a
+specified command
+or by interacting with a Unix domain socket.
+This transport is something of a cross between the \%pipe%\ and \%smtp%\
+transports. Exim also has support for using LMTP over TCP/IP; this is
+implemented as an option for the \%smtp%\ transport. Because LMTP is expected
+to be of minority interest, the default build-time configure in \(src/EDITME)\
+has it commented out. You need to ensure that
+.display asis
+TRANSPORT_LMTP=yes
+.endd
+is present in your \(Local/Makefile)\ in order to have the \%lmtp%\ transport
+included in the Exim binary.
+
+The private options of the \%lmtp%\ transport are as follows:
+
+.startconf
+.index options||\%lmtp%\ transport
+
+.conf batch@_id string$**$ unset
+See the description of local delivery batching in chapter ~~CHAPbatching.
+
+.conf batch@_max integer 1
+This limits the number of addresses that can be handled in a single delivery.
+Most LMTP servers can handle several addresses at once, so it is normally a
+good idea to increase this value. See the description of local delivery
+batching in chapter ~~CHAPbatching.
+
+.conf command string$**$ unset
+This option must be set if \socket\ is not set.
+The string is a command which is run in a separate process. It is split up into
+a command name and list of arguments, each of which is separately expanded (so
+expansion cannot change the number of arguments). The command is run directly,
+not via a shell. The message is passed to the new process using the standard
+input and output to operate the LMTP protocol.
+
+.conf socket string$**$ unset
+This option must be set if \command\ is not set. The result of expansion must
+be the name of a Unix domain socket. The transport connects to the socket and
+delivers the message to it using the LMTP protocol.
+
+.conf timeout time 5m
+The transport is aborted if the created process
+or Unix domain socket
+does not respond to LMTP commands or message input within this timeout.
+
+.endconf
+
+Here is an example of a typical LMTP transport:
+.display asis
+lmtp:
+ driver = lmtp
+ command = /some/local/lmtp/delivery/program
+ batch_max = 20
+ user = exim
+.endd
+This delivers up to 20 addresses at a time, in a mixture of domains if
+necessary, running as the user \*exim*\.
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The pipe transport
+.rset CHAPpipetransport "~~chapter"
+.set runningfoot "pipe transport"
+.index transports||\%pipe%\
+.index \%pipe%\ transport
+The \%pipe%\ transport is used to deliver messages via a pipe to a command
+running in another process. This can happen in one of two ways:
+.numberpars $.
+A router routes an address to a transport in the normal way, and the transport
+is configured as a \%pipe%\ transport. In this case, \$local@_part$\ contains
+the address (as usual), and the command which is run is specified by the
+\command\ option on the transport. An example of this is the use of \%pipe%\ as
+a pseudo-remote transport for passing messages to some other delivery mechanism
+(such as UUCP).
+.nextp
+A router redirects an address directly to a pipe command (for example, from an
+alias or forward file). In this case, \$local@_part$\ contains the local part
+that was redirected, and \$address@_pipe$\ contains the text of the pipe
+command itself. The \command\ option on the transport is ignored.
+.endp
+
+The \%pipe%\ transport is a non-interactive delivery method. Exim can also
+deliver messages over pipes using the LMTP interactive protocol. This is
+implemented by the \%lmtp%\ transport.
+
+In the case when \%pipe%\ is run as a consequence of an entry in a local user's
+\(.forward)\ file, the command runs under the uid and gid of that user. In
+other cases, the uid and gid have to be specified explicitly, either on the
+transport or on the router that handles the address. Current and `home'
+directories are also controllable. See chapter ~~CHAPenvironment for details of
+the local delivery environment.
+
+.section Returned status and data
+.index \%pipe%\ transport||returned data
+If the command exits with a non-zero return code, the delivery is deemed to
+have failed, unless either the \ignore@_status\ option is set (in which case
+the return code is treated as zero), or the return code is one of those listed
+in the \temp@_errors\ option, which are interpreted as meaning `try again
+later'. In this case, delivery is deferred. Details of a permanent failure are
+logged, but are not included in the bounce message, which merely contains
+`local delivery failed'.
+
+If the return code is greater than 128 and the command being run is a shell
+script, it normally means that the script was terminated by a signal whose
+value is the return code minus 128.
+
+If Exim is unable to run the command (that is, if \*execve()*\ fails), the
+return code is set to 127. This is the value that a shell returns if it is
+asked to run a non-existent command. The wording for the log line suggests that
+a non-existent command may be the problem.
+
+The \return@_output\ option can affect the result of a pipe delivery. If it is
+set and the command produces any output on its standard output or standard
+error streams, the command is considered to have failed, even if it gave a zero
+return code or if \ignore@_status\ is set. The output from the command is
+included as part of the bounce message. The \return@_fail@_output\ option is
+similar, except that output is returned only when the command exits with a
+failure return code, that is, a value other than zero or a code that matches
+\temp@_errors\.
+
+
+.section How the command is run
+.rset SECThowcommandrun "~~chapter.~~section"
+.index \%pipe%\ transport||path for command
+The command line is (by default) broken down into a command name and arguments
+by the \%pipe%\ transport itself. The \allow@_commands\ and \restrict@_to@_path\
+options can be used to restrict the commands that may be run.
+.index quoting||in pipe command
+Unquoted arguments are delimited by white space. If an argument appears in
+double quotes, backslash is interpreted as an escape character in the usual
+way. If an argument appears in single quotes, no escaping is done.
+
+String expansion is applied to the command line except when it comes from a
+traditional \(.forward)\ file (commands from a filter file are expanded). The
+expansion is applied to each argument in turn rather than to the whole line.
+For this reason, any string expansion item that contains white space must be
+quoted so as to be contained within a single argument. A setting such as
+.display asis
+command = /some/path ${if eq{$local_part}{postmaster}{xxx}{yyy}}
+.endd
+will not work, because the expansion item gets split between several
+arguments. You have to write
+.display asis
+command = /some/path "${if eq{$local_part}{postmaster}{xxx}{yyy}}"
+.endd
+to ensure that it is all in one argument. The expansion is done in this way,
+argument by argument, so that the number of arguments cannot be changed as a
+result of expansion, and quotes or backslashes in inserted variables do not
+interact with external quoting.
+
+.index transport||filter
+.index filter||transport filter
+Special handling takes place when an argument consists of precisely the text
+`$tt{@$pipe@_addresses}'. This is not a general expansion variable; the only
+place this string is recognized is when it appears as an argument for a pipe or
+transport filter command. It causes each address that is being handled to be
+inserted in the argument list at that point $it{as a separate argument}. This
+avoids any problems with spaces or shell metacharacters, and is of use when a
+\%pipe%\ transport is handling groups of addresses in a batch.
+
+After splitting up into arguments and expansion, the resulting command is run
+in a subprocess directly from the transport, $it{not} under a shell. The
+message that is being delivered is supplied on the standard input, and the
+standard output and standard error are both connected to a single pipe that is
+read by Exim. The \max@_output\ option controls how much output the command may
+produce, and the \return@_output\ and \return@_fail@_output\ options control
+what is done with it.
+
+Not running the command under a shell (by default) lessens the security risks
+in cases when a command from a user's filter file is built out of data that was
+taken from an incoming message. If a shell is required, it can of course be
+explicitly specified as the command to be run. However, there are circumstances
+where existing commands (for example, in \(.forward)\ files) expect to be run
+under a shell and cannot easily be modified. To allow for these cases, there is
+an option called \use@_shell\, which changes the way the \%pipe%\ transport
+works. Instead of breaking up the command line as just described, it expands it
+as a single string and passes the result to \(/bin/sh)\. The
+\restrict@_to@_path\ option and the \$pipe@_addresses$\ facility cannot be used
+with \use@_shell\, and the whole mechanism is inherently less secure.
+
+
+.section Environment variables
+.rset SECTpipeenv "~~chapter.~~section"
+.index \%pipe%\ transport||environment for command
+.index environment for pipe transport
+The environment variables listed below are set up when the command is invoked.
+This list is a compromise for maximum compatibility with other MTAs. Note that
+the \environment\ option can be used to add additional variables to this
+environment.
+.display flow
+.tabs 20
+DOMAIN $t $rm{the domain of the address}
+HOME $t $rm{the home directory, if set}
+HOST $t $rm{the host name when called from a router (see below)}
+LOCAL@_PART $t $rm{see below}
+LOCAL@_PART@_PREFIX $t $rm{see below}
+LOCAL@_PART@_SUFFIX $t $rm{see below}
+LOGNAME $t $rm{see below}
+MESSAGE@_ID $t $rm{the message's id}
+PATH $t $rm{as specified by the \path\ option below}
+QUALIFY@_DOMAIN $t $rm{the sender qualification domain}
+RECIPIENT $t $rm{the complete recipient address}
+SENDER $t $rm{the sender of the message (empty if a bounce)}
+SHELL $t `$tt{/bin/sh}'
+TZ $t $rm{the value of the \timezone\ option, if set}
+USER $t $rm{see below}
+.endd
+
+When a \%pipe%\ transport is called directly from (for example) an \%accept%\
+router, \\LOCAL@_PART\\ is set to the local part of the address. When it is
+called as a result of a forward or alias expansion, \\LOCAL@_PART\\ is set to
+the local part of the address that was expanded. In both cases, any affixes are
+removed from the local part, and made available in \\LOCAL@_PART@_PREFIX\\ and
+\\LOCAL@_PART@_SUFFIX\\, respectively. \\LOGNAME\\ and \\USER\\ are set to the
+same value as \\LOCAL@_PART\\ for compatibility with other MTAs.
+
+.index \\HOST\\
+\\HOST\\ is set only when a \%pipe%\ transport is called from a router that
+associates hosts with an address, typically when using \%pipe%\ as a
+pseudo-remote transport. \\HOST\\ is set to the first host name specified by
+the router.
+
+.index \\HOME\\
+If the transport's generic \home@_directory\ option is set, its value is used
+for the \\HOME\\ environment variable. Otherwise, a home directory may be set
+by the router's \transport@_home@_directory\ option, which defaults to the
+user's home directory if \check@_local@_user\ is set.
+
+.section Private options for pipe
+.index options||\%pipe%\ transport
+.startconf
+
+.conf allow@_commands "string list$**$" unset
+.index \%pipe%\ transport||permitted commands
+The string is expanded, and is then interpreted as a colon-separated list of
+permitted commands. If \restrict@_to@_path\ is not set, the only commands
+permitted are those in the \allow@_commands\ list. They need not be absolute
+paths; the \path\ option is still used for relative paths. If
+\restrict@_to@_path\ is set with \allow@_commands\, the command must either be
+in the \allow@_commands\ list, or a name without any slashes that is found on
+the path. In other words, if neither \allow@_commands\ nor \restrict@_to@_path\
+is set, there is no restriction on the command, but otherwise only commands
+that are permitted by one or the other are allowed. For example, if
+.display asis
+allow_commands = /usr/bin/vacation
+.endd
+and \restrict@_to@_path\ is not set, the only permitted command is
+\(/usr/bin/vacation)\. The \allow@_commands\ option may not be set if
+\use@_shell\ is set.
+
+.conf batch@_id string$**$ unset
+See the description of local delivery batching in chapter ~~CHAPbatching.
+
+.conf batch@_max integer 1
+This limits the number of addresses that can be handled in a single delivery.
+See the description of local delivery batching in chapter ~~CHAPbatching.
+
+.conf check@_string string unset
+As \%pipe%\ writes the message, the start of each line is tested for matching
+\check@_string\, and if it does, the initial matching characters are replaced
+by the contents of \escape@_string\, provided both are set. The value of
+\check@_string\ is a literal string, not a regular expression, and the case of
+any letters it contains is significant. When \use@_bsmtp\ is set, the contents
+of \check@_string\ and \escape@_string\ are forced to values that implement the
+SMTP escaping protocol. Any settings made in the configuration file are
+ignored.
+
+.conf command string$**$ unset
+This option need not be set when \%pipe%\ is being used to deliver to pipes
+obtained directly from address redirections. In other cases, the option must be
+set, to provide a command to be run. It need not yield an absolute path (see
+the \path\ option below). The command is split up into separate arguments by
+Exim, and each argument is separately expanded, as described in section
+~~SECThowcommandrun above.
+
+.conf environment string$**$ unset
+.index \%pipe%\ transport||environment for command
+.index environment for \%pipe%\ transport
+This option is used to add additional variables to the environment in which the
+command runs (see section ~~SECTpipeenv for the default list). Its value is a
+string which is expanded, and then interpreted as a colon-separated list of
+environment settings of the form `<<name>>=<<value>>'.
+
+.conf escape@_string string unset
+See \check@_string\ above.
+
+.conf freeze@_exec@_fail boolean false
+.index exec failure
+.index failure of exec
+.index \%pipe%\ transport||failure of exec
+Failure to exec the command in a pipe transport is by default treated like
+any other failure while running the command. However, if \freeze@_exec@_fail\
+is set, failure to exec is treated specially, and causes the message to be
+frozen, whatever the setting of \ignore@_status\.
+
+.conf ignore@_status boolean false
+If this option is true, the status returned by the subprocess that is set up to
+run the command is ignored, and Exim behaves as if zero had been returned.
+Otherwise, a non-zero status
+or termination by signal
+causes an error return from the transport unless the status value is one of
+those listed in \temp@_errors\; these cause the delivery to be deferred and
+tried again later.
+
+.conf log@_defer@_output boolean false
+.index \%pipe%\ transport||logging output
+If this option is set, and the status returned by the command is
+one of the codes listed in \temp@_errors\ (that is, delivery was deferred),
+and any output was produced, the first line of it is written to the main log.
+
+.conf log@_fail@_output boolean false
+If this option is set, and the command returns any output, and also ends with a
+return code that is neither zero nor one of the return codes listed in
+\temp@_errors\ (that is, the delivery failed), the first line of output is
+written to the main log.
+
+.conf log@_output boolean false
+If this option is set and the command returns any output, the first line of
+output is written to the main log, whatever the return code.
+
+.conf max@_output integer 20K
+This specifies the maximum amount of output that the command may produce on its
+standard output and standard error file combined. If the limit is exceeded, the
+process running the command is killed. This is intended as a safety measure to
+catch runaway processes. The limit is applied independently of the settings of
+the options that control what is done with such output (for example,
+\return@_output\). Because of buffering effects, the amount of output may
+exceed the limit by a small amount before Exim notices.
+
+.conf message@_prefix string$**$ "see below"
+The string specified here is expanded and output at the start of every message.
+The default is unset if \use@_bsmtp\ is set. Otherwise it is
+.display asis
+message_prefix = \
+ From ${if def:return_path{$return_path}{MAILER-DAEMON}}\
+ ${tod_bsdinbox}\n
+.endd
+.index Cyrus
+.index \tmail\
+.index `From' line
+This is required by the commonly used \(/usr/bin/vacation)\ program.
+However, it must $it{not} be present if delivery is to the Cyrus IMAP server,
+or to the \tmail\ local delivery agent. The prefix can be suppressed by setting
+.display asis
+message_prefix =
+.endd
+
+.conf message@_suffix string$**$ "see below"
+The string specified here is expanded and output at the end of every message.
+The default is unset if \use@_bsmtp\ is set. Otherwise it is a single newline.
+The suffix can be suppressed by setting
+.display asis
+message_suffix =
+.endd
+
+.conf path string $tt{/usr/bin}
+This option specifies the string that is set up in the \\PATH\\ environment
+variable of the subprocess. If the \command\ option does not yield an absolute
+path name, the command is sought in the \\PATH\\ directories, in the usual way.
+\**Warning**\: This does not apply to a command specified as a transport
+filter.
+
+.conf pipe@_as@_creator boolean false
+.index uid (user id)||local delivery
+If the generic \user\ option is not set and this option is true, the delivery
+process is run under the uid that was in force when Exim was originally called
+to accept the message. If the group id is not otherwise set (via the generic
+\group\ option), the gid that was in force when Exim was originally called to
+accept the message is used.
+
+.conf restrict@_to@_path boolean false
+When this option is set, any command name not listed in \allow@_commands\ must
+contain no slashes. The command is searched for only in the directories listed
+in the \path\ option. This option is intended for use in the case when a pipe
+command has been generated from a user's \(.forward)\ file. This is usually
+handled by a \%pipe%\ transport called \address@_pipe\.
+
+.conf return@_fail@_output boolean false
+If this option is true, and the command produced any output and ended with a
+return code other than zero or one of the codes listed in \temp@_errors\ (that
+is, the delivery failed), the output is returned in the bounce message.
+However, if the message has a null sender (that is, it is itself a bounce
+message), output from the command is discarded.
+
+.conf return@_output boolean false
+If this option is true, and the command produced any output, the delivery is
+deemed to have failed whatever the return code from the command, and the output
+is returned in the bounce message. Otherwise, the output is just discarded.
+However, if the message has a null sender (that is, it is a bounce message),
+output from the command is always discarded, whatever the setting of this
+option.
+
+.conf temp@_errors "string list" "see below"
+.index \%pipe%\ transport||temporary failure
+This option contains either a colon-separated list of numbers, or a single
+asterisk. If \ignore@_status\ is false
+.em
+and \return@_output\ is not set,
+.nem
+and the command exits with a non-zero return code, the failure is treated as
+temporary and the delivery is deferred if the return code matches one of the
+numbers, or if the setting is a single asterisk. Otherwise, non-zero return
+codes are treated as permanent errors. The default setting contains the codes
+defined by \\EX@_TEMPFAIL\\ and \\EX@_CANTCREAT\\ in \(sysexits.h)\. If Exim is
+compiled on a system that does not define these macros, it assumes values of 75
+and 73, respectively.
+
+.conf timeout time 1h
+If the command fails to complete within this time, it is killed. This normally
+causes the delivery to fail. A zero time interval specifies no timeout. In
+order to ensure that any subprocesses created by the command are also killed,
+Exim makes the initial process a process group leader, and kills the whole
+process group on a timeout. However, this can be defeated if one of the
+processes starts a new process group.
+
+.conf umask "octal integer" 022
+This specifies the umask setting for the subprocess that runs the command.
+
+.conf use@_bsmtp boolean false
+.index envelope sender
+If this option is set true, the \%pipe%\ transport writes messages in `batch
+SMTP' format, with the envelope sender and recipient(s) included as SMTP
+commands. If you want to include a leading \\HELO\\ command with such messages,
+you can do so by setting the \message@_prefix\ option. See section
+~~SECTbatchSMTP for details of batch SMTP.
+
+.conf use@_crlf boolean false
+.index carriage return
+.index linefeed
+This option causes lines to be terminated with the two-character CRLF sequence
+(carriage return, linefeed) instead of just a linefeed character. In the case
+of batched SMTP, the byte sequence written to the pipe is then an exact image
+of what would be sent down a real SMTP connection.
+
+The contents of the \message@_prefix\ and \message@_suffix\ options are written
+verbatim, so must contain their own carriage return characters if these are
+needed. Since the default values for both \message@_prefix\ and
+\message@_suffix\ end with a single linefeed, their values
+must
+be changed to end with \"@\r@\n"\ if \use@_crlf\ is set.
+
+.conf use@_shell boolean false
+If this option is set, it causes the command to be passed to \(/bin/sh)\
+instead of being run directly from the transport, as described in section
+~~SECThowcommandrun. This is less secure, but is needed in some situations
+where the command is expected to be run under a shell and cannot easily be
+modified. The \allow@_commands\ and \restrict@_to@_path\ options, and the
+`$tt{@$pipe@_addresses}' facility are incompatible with \use@_shell\. The
+command is expanded as a single string, and handed to \(/bin/sh)\ as data for
+its \-c-\ option.
+
+.endconf
+
+.section Using an external local delivery agent
+.index local delivery||using an external agent
+.index \*procmail*\
+.index external local delivery
+.index delivery||\*procmail*\
+.index delivery||by external agent
+The \%pipe%\ transport can be used to pass all messages that require local
+delivery to a separate local delivery agent such as \procmail\. When doing
+this, care must be taken to ensure that the pipe is run under an appropriate
+uid and gid. In some configurations one wants this to be a uid that is trusted
+by the delivery agent to supply the correct sender of the message. It may be
+necessary to recompile or reconfigure the delivery agent so that it trusts an
+appropriate user. The following is an example transport and router
+configuration for \procmail\:
+.display asis
+# transport
+procmail_pipe:
+ driver = pipe
+ command = /usr/local/bin/procmail -d $local_part
+ return_path_add
+ delivery_date_add
+ envelope_to_add
+ check_string = "From "
+ escape_string = ">From "
+ user = $local_part
+ group = mail
+.endd
+.display asis
+# router
+procmail:
+ driver = accept
+ check_local_user
+ transport = procmail_pipe
+.endd
+
+In this example, the pipe is run as the local user, but with the group set to
+\*mail*\. An alternative is to run the pipe as a specific user such as \*mail*\
+or \*exim*\, but in this case you must arrange for \procmail\ to trust that
+user to supply a correct sender address. If you do not specify either a \group\
+or a \user\ option, the pipe command is run as the local user. The home
+directory is the user's home directory by default.
+
+Note that the command that the pipe transport runs does $it{not} begin with
+.display asis
+IFS=" "
+.endd
+as shown in the \procmail\ documentation, because Exim does not by default use
+a shell to run pipe commands.
+
+.index Cyrus
+The next example shows a transport and a router for a system where local
+deliveries are handled by the Cyrus IMAP server.
+.display asis
+# transport
+local_delivery_cyrus:
+ driver = pipe
+ command = /usr/cyrus/bin/deliver \
+ -m ${substr_1:$local_part_suffix} -- $local_part
+ user = cyrus
+ group = mail
+ return_output
+ log_output
+ message_prefix =
+ message_suffix =
+.endd
+.display asis
+# router
+local_user_cyrus:
+ driver = accept
+ check_local_user
+ local_part_suffix = .*
+ transport = local_delivery_cyrus
+.endd
+Note the unsetting of \message@_prefix\ and \message@_suffix\, and the use of
+\return@_output\ to cause any text written by Cyrus to be returned to the
+sender.
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The smtp transport
+.rset CHAPsmtptrans "~~chapter"
+.set runningfoot "smtp transport"
+.index transports||\%smtp%\
+.index \%smtp%\ transport
+The \%smtp%\ transport delivers messages over TCP/IP connections using the SMTP
+or LMTP protocol. The list of hosts to try can either be taken from the address
+that is being processed (having been set up by the router), or specified
+explicitly for the transport. Timeout and retry processing (see chapter
+~~CHAPretry) is applied to each IP address independently.
+
+.section Multiple messages on a single connection
+The sending of multiple messages over a single TCP/IP connection can arise in
+two ways:
+.numberpars $.
+If a message contains more than \max@_rcpt\ (see below) addresses that are
+routed to the same host, more than one copy of the message has to be sent to
+that host. In this situation, multiple copies may be sent in a single run of
+the \%smtp%\ transport over a single TCP/IP connection. (What Exim actually does
+when it has too many addresses to send in one message also depends on the value
+of the global \remote@_max@_parallel\ option. Details are given in section
+~~SECToutSMTPTCP.)
+.nextp
+.index hints database||remembering routing
+When a message has been successfully delivered over a TCP/IP connection, Exim
+looks in its hints database to see if there are any other messages awaiting a
+connection to the same host. If there are, a new delivery process is started
+for one of them, and the current TCP/IP connection is passed on to it. The new
+process may in turn send multiple copies and possibly create yet another
+process.
+.endp
+
+For each copy sent over the same TCP/IP connection, a sequence counter is
+incremented, and if it ever gets to the value of \connection@_max@_messages\,
+no further messages are sent over that connection.
+
+
+.section Use of the @$host variable
+.index \$host$\
+.index \$host@_address$\
+At the start of a run of the \%smtp%\ transport, the values of \$host$\ and
+\$host@_address$\ are the name and IP address of the first host on the host list
+passed by the router. However, when the transport is about to connect to a
+specific host, and while it is connected to that host, \$host$\ and
+\$host@_address$\ are set to the values for that host. These are the values
+that are in force when the \helo@_data\, \hosts@_try@_auth\, \interface\,
+\serialize@_hosts\, and the various TLS options are expanded.
+
+
+.section Private options for smtp
+The private options of the \%smtp%\ transport are as follows:
+
+.index options||\%smtp%\ transport
+.startconf
+.conf allow@_localhost boolean false
+.index local host||sending to
+.index fallback||hosts specified on transport
+When a host specified in \hosts\ or \fallback@_hosts\ (see below) turns out to
+be the local host, or is listed in \hosts@_treat@_as@_local\, delivery is
+deferred by default. However, if \allow@_localhost\ is set, Exim goes on to do
+the delivery anyway. This should be used only in special cases when the
+configuration ensures that no looping will result (for example, a differently
+configured Exim is listening on the port to which the message is sent).
+
+.conf authenticated@_sender string$**$ unset
+.index Cyrus
+When Exim has authenticated as a client, this option sets a value for the
+\\AUTH=\\ item on outgoing \\MAIL\\ commands, overriding any existing
+authenticated sender value. If the string expansion is forced to fail, the
+option is ignored. Other expansion failures cause delivery to be deferred. If
+the result of expansion is an empty string, that is also ignored.
+
+If the SMTP session is not authenticated, the expansion of
+\authenticated@_sender\ still happens (and can cause the delivery to be
+deferred if it fails), but no \\AUTH=\\ item is added to \\MAIL\\ commands.
+
+This option allows you to use the \%smtp%\ transport in LMTP mode to
+deliver mail to Cyrus IMAP and provide the proper local part as the
+`authenticated sender', via a setting such as:
+.display asis
+authenticated_sender = $local_part
+.endd
+This removes the need for IMAP subfolders to be assigned special ACLs to
+allow direct delivery to those subfolders.
+
+Because of expected uses such as that just described for Cyrus (when no
+domain is involved), there is no checking on the syntax of the provided
+value.
+
+.conf command@_timeout time 5m
+This sets a timeout for receiving a response to an SMTP command that has been
+sent out. It is also used when waiting for the initial banner line from the
+remote host. Its value must not be zero.
+
+.conf connect@_timeout time 5m
+This sets a timeout for the \*connect()*\ function, which sets up a TCP/IP call
+to a remote host. A setting of zero allows the system timeout (typically
+several minutes) to act. To have any effect, the value of this option must be
+less than the system timeout. However, it has been observed that on some
+systems there is no system timeout, which is why the default value for this
+option is 5 minutes, a value recommended by RFC 1123.
+
+.index SMTP||passed connection
+.index SMTP||multiple deliveries
+.index multiple SMTP deliveries
+.conf connection@_max@_messages integer 500
+This controls the maximum number of separate message deliveries that are sent
+over a single TCP/IP connection. If the value is zero, there is no limit.
+For testing purposes, this value can be overridden by the \-oB-\ command line
+option.
+
+.conf data@_timeout time 5m
+This sets a timeout for the transmission of each block in the data portion of
+the message. As a result, the overall timeout for a message depends on the size
+of the message. Its value must not be zero. See also \final@_timeout\.
+
+.conf delay@_after@_cutoff boolean true
+This option controls what happens when all remote IP addresses for a given
+domain have been inaccessible for so long that they have passed their retry
+cutoff times.
+
+In the default state, if the next retry time has not been reached for any of
+them, the address is bounced without trying any deliveries. In other words,
+Exim delays retrying an IP address after the final cutoff time until a new
+retry time is reached, and can therefore bounce an address without ever trying
+a delivery, when machines have been down for a long time. Some people are
+unhappy at this prospect, so...
+
+If \delay@_after@_cutoff\ is set false, Exim behaves differently. If all IP
+addresses are past their final cutoff time, Exim tries to deliver to those
+IP addresses that have not been tried since the message arrived. If there are
+none, of if they all fail, the address is bounced. In other words, it does not
+delay when a new message arrives, but immediately tries those expired IP
+addresses that haven't been tried since the message arrived. If there is a
+continuous stream of messages for the dead hosts, unsetting
+\delay@_after@_cutoff\ means that there will be many more attempts to deliver
+to them.
+
+.conf dns@_qualify@_single boolean true
+If the \hosts\ or \fallback@_hosts\ option is being used,
+and the \gethostbyname\ option is false,
+the \\RES@_DEFNAMES\\ resolver option is set. See the \qualify@_single\ option
+in chapter ~~CHAPdnslookup for more details.
+
+.conf dns@_search@_parents boolean false
+.index \search@_parents\
+If the \hosts\ or \fallback@_hosts\ option is being used, and the
+\gethostbyname\ option is false, the \\RES@_DNSRCH\\ resolver option is set.
+See the \search@_parents\ option in chapter ~~CHAPdnslookup for more details.
+
+
+.conf fallback@_hosts "string list" unset
+.index fallback||hosts specified on transport
+String expansion is not applied to this option. The argument must be a
+colon-separated list of host names or IP addresses. Fallback hosts can also be
+specified on routers, which associate them with the addresses they process. As
+for the \hosts\ option without \hosts@_override\, \fallback@_hosts\ specified
+on the transport is used only if the address does not have its own associated
+fallback host list. Unlike \hosts\, a setting of \fallback@_hosts\ on an
+address is not overridden by \hosts@_override\. However, \hosts@_randomize\
+does apply to fallback host lists.
+
+If Exim is unable to deliver to any of the hosts for a particular address, and
+the errors are not permanent rejections, the address is put on a separate
+transport queue with its host list replaced by the fallback hosts, unless the
+address was routed via MX records and the current host was in the original MX
+list. In that situation, the fallback host list is not used.
+
+Once normal deliveries are complete, the fallback queue is delivered by
+re-running the same transports with the new host lists. If several failing
+addresses have the same fallback hosts (and \max@_rcpt\ permits it), a single
+copy of the message is sent.
+
+The resolution of the host names on the fallback list is controlled by the
+\gethostbyname\ option, as for the \hosts\ option. Fallback hosts apply
+both to cases when the host list comes with the address and when it is taken
+from \hosts\. This option provides a `use a smart host only if delivery fails'
+facility.
+
+.conf final@_timeout time 10m
+This is the timeout that applies while waiting for the response to the final
+line containing just `.' that terminates a message. Its value must not be zero.
+
+.conf gethostbyname boolean false
+If this option is true when the \hosts\ and/or \fallback@_hosts\ options are
+being used, names are looked up using \*gethostbyname()*\
+(or \*getipnodebyname()*\ when available)
+instead of using the DNS. Of course, that function may in fact use the DNS, but
+it may also consult other sources of information such as \(/etc/hosts)\.
+
+.index \\HELO\\||argument, setting
+.index \\EHLO\\||argument, setting
+.conf helo@_data string$**$ $tt{@$primary@_hostname}
+The value of this option is expanded, and used as the argument for the \\EHLO\\
+or \\HELO\\ command that starts the outgoing SMTP session.
+
+.conf hosts "string list$**$" unset
+Hosts are associated with an address by a router such as \%dnslookup%\, which
+finds the hosts by looking up the address domain in the DNS. However, addresses
+can be passed to the \%smtp%\ transport by any router, and not all of them can
+provide an associated host list. The \hosts\ option specifies a list of hosts
+which are used if the address being processed does not have any hosts
+associated with it. The hosts specified by \hosts\ are also used, whether or
+not the address has its own hosts, if \hosts@_override\ is set.
+
+The string is first expanded, before being interpreted as a colon-separated
+list of host names or IP addresses. If the expansion fails, delivery is
+deferred. Unless the failure was caused by the inability to complete a lookup,
+the error is logged to the panic log as well as the main log. Host names are
+looked up either by searching directly for address records in the DNS or by
+calling \*gethostbyname()*\
+(or \*getipnodebyname()*\ when available),
+depending on the setting of the \gethostbyname\ option. When Exim is compiled
+with IPv6 support, if a host that is looked up in the DNS has both IPv4 and
+IPv6 addresses, both types of address are used.
+
+During delivery, the hosts are tried in order, subject to their retry status,
+unless \hosts@_randomize\ is set.
+
+.conf hosts@_avoid@_esmtp "host list$**$" unset
+.index ESMTP, avoiding use of
+.index \\HELO\\||forcing use of
+.index \\EHLO\\||avoiding use of
+.index \\PIPELINING\\||avoiding the use of
+This option is for use with broken hosts that announce ESMTP facilities (for
+example, \\PIPELINING\\) and then fail to implement them properly. When a host
+matches \hosts@_avoid@_esmtp\, Exim sends \\HELO\\ rather than \\EHLO\\ at the
+start of the SMTP session. This means that it cannot use any of the ESMTP
+facilities such as \\AUTH\\, \\PIPELINING\\, \\SIZE\\, and \\STARTTLS\\.
+
+.conf hosts@_avoid@_tls "host list$**$" unset
+.index TLS||avoiding for certain hosts
+Exim will not try to start a TLS session when delivering to any host that
+matches this list. See chapter ~~CHAPTLS for details of TLS.
+
+.conf hosts@_max@_try integer 5
+.index host||maximum number to try
+.index limit||number of hosts tried
+.index limit||number of MX tried
+.index MX record||maximum tried
+This option limits the number of IP addresses that are tried for any one
+delivery
+.em
+in cases where there are temporary delivery errors.
+.nem
+Section ~~SECTvalhosmax describes in detail how the value of this option is
+used.
+
+.conf hosts@_nopass@_tls "host list$**$" unset
+.index TLS||passing connection
+.index multiple SMTP deliveries
+.index TLS||multiple message deliveries
+For any host that matches this list, a connection on which a TLS session has
+been started will not be passed to a new delivery process for sending another
+message on the same connection. See section ~~SECTmulmessam for an explanation
+of when this might be needed.
+
+.conf hosts@_override boolean false
+If this option is set and the \hosts\ option is also set, any hosts that are
+attached to the address are ignored, and instead the hosts specified by the
+\hosts\ option are always used. This option does not apply to
+\fallback@_hosts\.
+
+.conf hosts@_randomize boolean false
+.index randomized host list
+.index host||list of, randomized
+.index fallback||randomized hosts
+If this option is set, and either the list of hosts is taken from the
+\hosts\ or the \fallback@_hosts\ option, or the hosts supplied by the router
+were not obtained from MX records (this includes fallback hosts from the
+router), and were not randomizied by the router, the order of trying the hosts
+is randomized each time the transport runs. Randomizing the order of a host
+list can be used to do crude load sharing.
+
+When \hosts@_randomize\ is true, a host list may be split into groups whose
+order is separately randomized. This makes it possible to set up MX-like
+behaviour. The boundaries between groups are indicated by an item that is just
+\"+"\ in the host list. For example:
+.display asis
+hosts = host1:host2:host3:+:host4:host5
+.endd
+The order of the first three hosts and the order of the last two hosts is
+randomized for each use, but the first three always end up before the last two.
+If \hosts@_randomize\ is not set, a \"+"\ item in the list is ignored.
+
+.index authentication||required by client
+.conf hosts@_require@_auth "host list$**$" unset
+This option provides a list of servers for which authentication must succeed
+before Exim will try to transfer a message. If authentication fails for
+servers which are not in this list, Exim tries to send unauthenticated. If
+authentication fails for one of these servers, delivery is deferred. This
+temporary error is detectable in the retry rules, so it can be turned into a
+hard failure if required. See also \hosts@_try@_auth\, and chapter
+~~CHAPSMTPAUTH for details of authentication.
+
+.conf hosts@_require@_tls "host list$**$" unset
+.index TLS||requiring for certain servers
+Exim will insist on using a TLS session when delivering to any host that
+matches this list. See chapter ~~CHAPTLS for details of TLS.
+\**Note**\: This option affects outgoing mail only. To insist on TLS for
+incoming messages, use an appropriate ACL.
+
+.index authentication||optional in client
+.conf hosts@_try@_auth "host list$**$" unset
+This option provides a list of servers to which, provided they announce
+authentication support, Exim will attempt to authenticate as a client when it
+connects. If authentication fails, Exim will try to transfer the message
+unauthenticated. See also \hosts@_require@_auth\, and chapter ~~CHAPSMTPAUTH
+for details of authentication.
+
+.index bind IP address
+.index IP address||binding
+.conf interface "string list$**$" unset
+This option specifies which interface to bind to when making an outgoing SMTP
+call. The variables \$host$\ and \$host@_address$\ refer to the host to which a
+connection is about to be made during the expansion of the string. Forced
+expansion failure, or an empty string result causes the option to be ignored.
+Otherwise, after expansion,
+.em
+the string must be a list of IP addresses, colon-separated by default, but the
+separator can be changed in the usual way.
+.nem
+For example:
+.display asis
+interface = <; 192.168.123.123 ; 3ffe:ffff:836f::fe86:a061
+.endd
+The first interface of the correct type (IPv4 or IPv6) is used for the outgoing
+connection. If none of them are the correct type, the option is ignored. If
+\interface\ is not set, or is ignored, the system's IP functions choose which
+interface to use if the host has more than one.
+
+.conf keepalive boolean true
+.index keepalive||on outgoing connection
+This option controls the setting of \\SO@_KEEPALIVE\\ on outgoing TCP/IP socket
+connections. When set, it causes the kernel to probe idle connections
+periodically, by sending packets with `old' sequence numbers. The other end of
+the connection should send a acknowledgement if the connection is still okay or
+a reset if the connection has been aborted. The reason for doing this is that
+it has the beneficial effect of freeing up certain types of connection that can
+get stuck when the remote host is disconnected without tidying up the TCP/IP
+call properly. The keepalive mechanism takes several hours to detect
+unreachable hosts.
+
+.conf max@_rcpt integer 100
+.index \\RCPT\\||maximum number of outgoing
+This option limits the number of \\RCPT\\ commands that are sent in a single
+SMTP message transaction. Each set of addresses is treated independently, and
+so can cause parallel connections to the same host if \remote@_max@_parallel\
+permits this.
+
+.conf multi@_domain boolean true
+When this option is set, the \%smtp%\ transport can handle a number of addresses
+containing a mixture of different domains provided they all resolve to the same
+list of hosts. Turning the option off restricts the transport to handling only
+one domain at a time. This is useful if you want to use \$domain$\ in an
+expansion for the transport, because it is set only when there is a single
+domain involved in a remote delivery.
+
+.conf port string$**$ "see below"
+.index port||sending TCP/IP
+.index TCP/IP||setting outgoing port
+This option specifies the TCP/IP port on the server to which Exim connects. If
+it begins with a digit it is taken as a port number; otherwise it is looked up
+using \*getservbyname()*\. The default value is normally `smtp', but if
+\protocol\ is set to `lmtp', the default is `lmtp'.
+If the expansion fails, or if a port number cannot be found, delivery is
+deferred.
+
+
+.conf protocol string "smtp"
+.index LMTP||over TCP/IP
+If this option is set to `lmtp' instead of `smtp', the default value for the
+\port\ option changes to `lmtp', and the transport operates the LMTP protocol
+(RFC 2033) instead of SMTP. This protocol is sometimes used for local
+deliveries into closed message stores. Exim also has support for running LMTP
+over a pipe to a local process -- see chapter ~~CHAPLMTP.
+
+.conf retry@_include@_ip@_address boolean true
+Exim normally includes both the host name and the IP address in the key it
+constructs for indexing retry data after a temporary delivery failure. This
+means that when one of several IP addresses for a host is failing, it gets
+tried periodically (controlled by the retry rules), but use of the other IP
+addresses is not affected.
+
+However, in some dialup environments hosts are assigned a different IP address
+each time they connect. In this situation the use of the IP address as part of
+the retry key leads to undesirable behaviour. Setting this option false causes
+Exim to use only the host name. This should normally be done on a separate
+instance of the \%smtp%\ transport, set up specially to handle the dialup hosts.
+
+.conf serialize@_hosts "host list$**$" unset
+.index serializing connections
+.index host||serializing connections
+Because Exim operates in a distributed manner, if several messages for the same
+host arrive at around the same time, more than one simultaneous connection to
+the remote host can occur. This is not usually a problem except when there is a
+slow link between the hosts. In that situation it may be helpful to restrict
+Exim to one connection at a time. This can be done by setting
+\serialize@_hosts\ to match the relevant hosts.
+
+.index hints database||serializing deliveries to a host
+Exim implements serialization by means of a hints database in which a record is
+written whenever a process connects to one of the restricted hosts. The record
+is deleted when the connection is completed. Obviously there is scope for
+records to get left lying around if there is a system or program crash. To
+guard against this, Exim ignores any records that are more than six hours old.
+
+If you set up this kind of serialization, you should also arrange to delete the
+relevant hints database whenever your system reboots. The names of the files
+start with \(misc)\ and they are kept in the \(spool/db)\ directory. There
+may be one or two files, depending on the type of DBM in use. The same files
+are used for ETRN serialization.
+
+.conf size@_addition integer 1024
+.index SMTP||\\SIZE\\
+.index message||size issue for transport filter
+.index size||of message
+.index transport||filter
+.index filter||transport filter
+If a remote SMTP server indicates that it supports the \\SIZE\\ option of the
+\\MAIL\\ command, Exim uses this to pass over the message size at the start of
+an SMTP transaction. It adds the value of \size@_addition\ to the value it
+sends, to allow for headers and other text that may be added during delivery by
+configuration options or in a transport filter. It may be necessary to increase
+this if a lot of text is added to messages.
+
+Alternatively, if the value of \size@_addition\ is set negative, it disables
+the use of the \\SIZE\\ option altogether.
+
+.conf tls@_certificate string$**$ unset
+.index TLS||client certificate, location of
+.index certificate||for client, location of
+The value of this option must be the absolute path to a file which contains the
+client's certificate, for use when sending a message over an encrypted
+connection. The values of \$host$\ and \$host@_address$\ are set to the name
+and address of the server during the expansion. See chapter ~~CHAPTLS for
+details of TLS.
+
+\**Note**\: This option must be set if you want Exim to use TLS when sending
+messages as a client. The global option of the same name specifies the
+certificate for Exim as a server; it is not automatically assumed that the same
+certificate should be used when Exim is operating as a client.
+
+.em
+.conf tls@_crl string$**$ unset
+.index TLS||client certificate revocation list
+.index certificate||revocation list for client
+This option specifies a certificate revocation list. The expanded value must
+be the name of a file that contains a CRL in PEM format.
+.nem
+
+.conf tls@_privatekey string$**$ unset
+.index TLS||client private key, location of
+The value of this option must be the absolute path to a file which contains the
+client's private key, for use when sending a message over an encrypted
+connection. The values of \$host$\ and \$host@_address$\ are set to the name
+and address of the server during the expansion.
+If this option is unset, the private key is assumed to be in the same file as
+the certificate.
+See chapter ~~CHAPTLS for details of TLS.
+
+.conf tls@_require@_ciphers string$**$ unset
+.index TLS||requiring specific ciphers
+.index cipher||requiring specific
+The value of this option must be a list of permitted cipher suites, for use
+when setting up an
+.em
+outgoing encrypted connection. (There is a global option of the same name for
+controlling incoming connections.)
+.nem
+The values of \$host$\ and \$host@_address$\ are set to the name and address of
+the server during the expansion. See chapter ~~CHAPTLS for details of TLS; note
+that this option is used in different ways by OpenSSL and GnuTLS (see section
+~~SECTreqciphsslgnu).
+
+.conf tls@_tempfail@_tryclear boolean true
+When the server host is not in \hosts@_require@_tls\, and there is a problem in
+setting up a TLS session, this option determines whether or not Exim should try
+to deliver the message unencrypted. If it is set false, delivery to the
+current host is deferred; if there are other hosts, they are tried. If this
+option is set true, Exim attempts to deliver unencrypted after a 4\*xx*\
+response to \\STARTTLS\\. Also, if \\STARTTLS\\ is accepted, but the subsequent
+TLS negotiation fails, Exim closes the current connection (because it is in an
+unknown state), opens a new one to the same host, and then tries the delivery
+in clear.
+
+.conf tls@_verify@_certificates string$**$ unset
+.index TLS||server certificate verification
+.index certificate||verification of server
+The value of this option must be the absolute path to a file containing
+permitted server certificates, for use when setting up an encrypted connection.
+Alternatively, if you are using OpenSSL, you can set
+\tls@_verify@_certificates\ to the name of a directory containing certificate
+files. This does not work with GnuTLS; the option must be set to the name of a
+single file if you are using GnuTLS. The values of \$host$\ and
+\$host@_address$\ are set to the name and address of the server during the
+expansion of this option. See chapter ~~CHAPTLS for details of TLS.
+
+.endconf
+
+
+.section How the value of hosts@_max@_try is used
+.rset SECTvalhosmax "~~chapter.~~section"
+.index host||maximum number to try
+.index limit||hosts, maximum number tried
+The \hosts@_max@_try\ option limits the number of hosts that are tried
+for a single delivery. However, despite the term `host' in its name, the option
+actually applies to each IP address independently. In other words, a multihomed
+host is treated as several independent hosts, just as it is for retrying.
+
+Many of the larger ISPs have multiple MX records which often point to
+multihomed hosts. As a result, a list of a dozen or more IP addresses may be
+created as a result of routing one of these domains.
+
+Trying every single IP address on such a long list does not seem sensible; if
+several at the top of the list fail, it is reasonable to assume there is some
+problem that is likely to affect all of them. Roughly speaking, the value of
+\hosts@_max@_try\ is the maximum number that are tried before deferring the
+delivery. However, the logic cannot be quite that simple.
+
+Firstly, IP addresses that are skipped because their retry times have not
+arrived do not count, and in addition, addresses that are past their retry
+limits are also not counted, even when they are tried. This means that when
+some IP addresses are past their retry limits, more than the value of
+\hosts@_max@_retry\ may be tried. The reason for this behaviour is to ensure
+that all IP addresses are considered before timing out an email address.
+
+Secondly, when the \hosts@_max@_try\ limit is reached, Exim looks down the host
+list to see if there is a subsequent host with a different (higher valued) MX.
+If there is, that host is used next, and the current IP address is used but not
+counted. This behaviour helps in the case of a domain with a retry rule that
+hardly ever delays any hosts, as is now explained:
+
+Consider the case of a long list of hosts with one MX value, and a few with a
+higher MX value. If \hosts@_max@_try\ is small (the default is 5) only a few
+hosts at the top of the list are tried at first. With the default retry rule,
+which specifies increasing retry times, the higher MX hosts are eventually
+tried when those at the top of the list are skipped because they have not
+reached their retry times.
+
+However, it is common practice to put a fixed short retry time on domains for
+large ISPs, on the grounds that their servers are rarely down for very long.
+Unfortunately, these are exactly the domains that tend to resolve to long lists
+of hosts. The short retry time means that the lowest MX hosts are tried every
+time. The attempts may be in a different order because of random sorting, but
+without the special MX check mentioned about, the higher MX hosts would never
+be tried at all because the lower MX hosts are never all past their retry
+times.
+
+With the special check, Exim tries least one address from each MX value, even
+if the \hosts@_max@_try\ limit has already been reached.
+
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Address rewriting
+.set runningfoot "address rewriting"
+.rset CHAPrewrite ~~chapter
+.index rewriting||addresses
+There are some circumstances in which Exim automatically rewrites domains in
+addresses. The two most common are when an address is given without a domain
+(referred to as an `unqualified address') or when an address contains an
+abbreviated domain that is expanded by DNS lookup.
+
+Unqualified envelope addresses are accepted only for locally submitted
+messages, or messages from hosts that match \sender@_unqualified@_hosts\ or
+\recipient@_unqualified@_hosts\, respectively. Unqualified addresses in header
+lines are qualified if they are in locally submitted messages, or messages from
+hosts that are permitted to send unqualified envelope addresses. Otherwise,
+unqualified addresses in header lines are neither qualified nor rewritten.
+
+One situation in which Exim does $it{not} automatically rewrite a domain is
+when it is the name of a CNAME record in the DNS. The older RFCs suggest that
+such a domain should be rewritten using the `canonical' name, and some MTAs do
+this. The new RFCs do not contain this suggestion.
+
+.section Explicitly configured address rewriting
+This chapter describes the rewriting rules that can be used in the
+main rewrite section of the configuration file, and also in the generic
+\headers@_rewrite\ option that can be set on any transport.
+
+Some people believe that configured address rewriting is a Mortal Sin.
+Others believe that life is not possible without it. Exim provides the
+facility; you do not have to use it.
+
+.em
+The main rewriting rules that appear in the `rewrite' section of the
+configuration file are applied to addresses in incoming messages, both envelope
+addresses and addresses in header lines. Each rule specifies the types of
+address to which it applies.
+.nem
+
+Rewriting of addresses in header lines applies only to those headers that
+were received with the message, and, in the case of transport rewriting, those
+that were added by a system filter. That is, it applies only to those headers
+that are common to all copies of the message. Header lines that are added by
+individual routers or transports (and which are therefore specific to
+individual recipient addresses) are not rewritten.
+
+In general, rewriting addresses from your own system or domain has some
+legitimacy. Rewriting other addresses should be done only with great care and
+in special circumstances. The author of Exim believes that rewriting should be
+used sparingly, and mainly for `regularizing' addresses in your own domains.
+Although it can sometimes be used as a routing tool, this is very strongly
+discouraged.
+
+There are two commonly encountered circumstances where rewriting is used, as
+illustrated by these examples:
+.numberpars $.
+The company whose domain is \*hitch.fict.example*\ has a number of hosts that
+exchange mail with each other behind a firewall, but there is only a single
+gateway to the outer world. The gateway rewrites \*@*.hitch.fict.example*\ as
+\*hitch.fict.example*\ when sending mail off-site.
+.nextp
+A host rewrites the local parts of its own users so that, for example,
+\*fp42@@hitch.fict.example*\ becomes \*Ford.Prefect@@hitch.fict.example*\.
+.endp
+
+.em
+.section When does rewriting happen?
+.index rewriting||timing of
+.index ~~ACL||rewriting addresses in
+Configured address rewriting can take place at several different stages of a
+message's processing.
+
+At the start of an ACL for \\MAIL\\, the sender address may have been rewritten
+by a special SMTP-time rewrite rule (see section ~~SECTrewriteS), but no
+ordinary rewrite rules have yet been applied. If, however, the sender address
+is verified in the ACL, it is rewritten before verification, and remains
+rewritten thereafter. The subsequent value of \$sender@_address$\ is the
+rewritten address. This also applies if sender verification happens in a
+\\RCPT\\ ACL. Otherwise, when the sender address is not verified, it is
+rewritten as soon as a message's header lines have been received.
+
+Similarly, at the start of an ACL for \\RCPT\\, the current recipient's address
+may have been rewritten by a special SMTP-time rewrite rule, but no ordinary
+rewrite rules have yet been applied to it. However, the behaviour is different
+from the sender address when a recipient is verified. The address is rewritten
+for the verification, but the rewriting is not remembered at this stage. The
+value of \$local@_part$\ and \$domain$\ after verification are always the same
+as they were before (that is, they contain the unrewritten -- except for
+SMTP-time rewriting -- address).
+
+Once a message's header lines have been received, all the envelope recipient
+addresses are permanently rewritten, and rewriting is also applied to the
+addresses in the header lines (if configured).
+.index \*local@_scan()*\ function||address rewriting, timing of
+Thus, all the rewriting is completed before the \\DATA\\ ACL and
+\*local@_scan()*\ functions are run.
+
+When an address is being routed, either for delivery or for verification,
+rewriting is applied immediately to child addresses that are generated by
+redirection, unless \no@_rewrite\ is set on the router.
+.nem
+
+.index envelope sender, rewriting
+.index rewriting||at transport time
+At transport time, additional rewriting of addresses in header lines can be
+specified by setting the generic \headers@_rewrite\ option on a transport. This
+option contains rules that are identical in form to those in the rewrite
+section of the configuration file. In addition, the outgoing envelope sender
+can be rewritten by means of the \return@_path\ transport option. However, it
+is not possible to rewrite envelope recipients at transport time.
+
+
+
+.section Testing the rewriting rules that apply on input
+.index rewriting||testing
+.index testing||rewriting
+Exim's input rewriting configuration appears in a part of the run time
+configuration file headed by `begin rewrite'. It can be tested by the \-brw-\
+command line option. This takes an address (which can be a full RFC 2822
+address) as its argument. The output is a list of how the address would be
+transformed by the rewriting rules for each of the different places it might
+appear in an incoming message, that is, for each different header and for the
+envelope sender and recipient fields. For example,
+.display asis
+exim -brw ph10@exim.workshop.example
+.endd
+might produce the output
+.display asis
+ sender: Philip.Hazel@exim.workshop.example
+ from: Philip.Hazel@exim.workshop.example
+ to: ph10@exim.workshop.example
+ cc: ph10@exim.workshop.example
+ bcc: ph10@exim.workshop.example
+reply-to: Philip.Hazel@exim.workshop.example
+env-from: Philip.Hazel@exim.workshop.example
+ env-to: ph10@exim.workshop.example
+.endd
+which shows that rewriting has been set up for that address when used in any of
+the source fields, but not when it appears as a recipient address. At the
+present time, there is no equivalent way of testing rewriting rules that are
+set for a particular transport.
+
+.section Rewriting rules
+.index rewriting||rules
+The rewrite section of the configuration file consists of lines of rewriting
+rules in the form
+.display
+<<source pattern>> <<replacement>> <<flags>>
+.endd
+Rewriting rules that are specified for the \headers@_rewrite\ generic transport
+option are given as a colon-separated list. Each item in the list takes the
+same form as a line in the main rewriting configuration
+(except that any colons must be doubled, of course).
+
+The formats of source patterns and replacement strings are described below.
+Each is terminated by white space, unless enclosed in double quotes, in which
+case normal quoting conventions apply inside the quotes. The flags are single
+characters which may appear in any order. Spaces and tabs between them are
+ignored.
+
+For each address that could potentially be rewritten, the rules are scanned in
+order, and replacements for the address from earlier rules can themselves be
+replaced by later rules (but see the `q' and `R' flags).
+
+The order in which addresses are rewritten is undefined, may change between
+releases, and must not be relied on, with one exception: when a message is
+received, the envelope sender is always rewritten first, before any header
+lines are rewritten. For example, the replacement string for a rewrite of an
+address in ::To:: must not assume that the message's address in ::From:: has (or
+has not) already been rewritten. However, a rewrite of ::From:: may assume that
+the envelope sender has already been rewritten.
+
+The variables \$local@_part$\ and \$domain$\ can be used in the replacement
+string to refer to the address that is being rewritten. Note that lookup-driven
+rewriting can be done by a rule of the form
+.display asis
+*@* ${lookup ...
+.endd
+where the lookup key uses \$1$\ and \$2$\ or \$local@_part$\ and \$domain$\ to
+refer to the address that is being rewritten.
+
+.section Rewriting patterns
+.index rewriting||patterns
+.index address list||in a rewriting pattern
+The source pattern in a rewriting rule is any item which may appear in an
+address list (see section ~~SECTaddresslist). It is in fact processed as a
+single-item address list, which means that it is expanded before being tested
+against the address.
+
+Domains in patterns should be given in lower case. Local parts in patterns are
+case-sensitive. If you want to do case-insensitive matching of local parts, you
+can use a regular expression that starts with \"^(?i)"\.
+
+.index numerical variables (\$1$\, \$2$\, etc)||in rewriting rules
+After matching, the numerical variables \$1$\, \$2$\, etc. may be set,
+depending on the type of match which occurred. These can be used in the
+replacement string to insert portions of the incoming address. \$0$\ always
+refers to the complete incoming address. When a regular expression is used, the
+numerical variables are set from its capturing subexpressions. For other types
+of pattern they are set as follows:
+
+.numberpars $.
+If a local part or domain starts with an asterisk, the numerical variables
+refer to the character strings matched by asterisks, with \$1$\ associated with
+the first asterisk, and \$2$\ with the second, if present. For example, if the
+pattern
+.display
+*queen@@*.fict.example
+.endd
+is matched against the address \*hearts-queen@@wonderland.fict.example*\ then
+.display asis
+$0 = hearts-queen@wonderland.fict.example
+$1 = hearts-
+$2 = wonderland
+.endd
+Note that if the local part does not start with an asterisk, but the domain
+does, it is \$1$\ that contains the wild part of the domain.
+.nextp
+If the domain part of the pattern is a partial lookup, the wild and fixed parts
+of the domain are placed in the next available numerical variables. Suppose,
+for example, that the address \*foo@@bar.baz.example*\ is processed by a
+rewriting rule of the form
+.display
+*@@partial-dbm;/some/dbm/file <<replacement string>>
+.endd
+and the key in the file that matches the domain is \"*.baz.example"\. Then
+.display asis
+$1 = foo
+$2 = bar
+$3 = baz.example
+.endd
+If the address \*foo@@baz.example*\ is looked up, this matches the same
+wildcard file entry, and in this case \$2$\ is set to the empty string, but
+\$3$\ is still set to \*baz.example*\. If a non-wild key is matched in a
+partial lookup, \$2$\ is again set to the empty string and \$3$\ is set to the
+whole domain. For non-partial domain lookups, no numerical variables are set.
+.endp
+
+.section Rewriting replacements
+.index rewriting||replacements
+If the replacement string for a rule is a single asterisk, addresses that
+match the pattern and the flags are $it{not} rewritten, and no subsequent
+rewriting rules are scanned. For example,
+.display asis
+hatta@lookingglass.fict.example * f
+.endd
+specifies that \*hatta@@lookingglass.fict.example*\ is never to be rewritten in
+::From:: headers.
+
+If the replacement string is not a single asterisk, it is expanded, and must
+yield a fully qualified address. Within the expansion, the variables
+\$local@_part$\ and \$domain$\ refer to the address that is being rewritten.
+Any letters they contain retain their original case -- they are not lower
+cased. The numerical variables are set up according to the type of pattern that
+matched the address, as described above. If the expansion is forced to fail by
+the presence of `fail' in a conditional or lookup item, rewriting by the
+current rule is abandoned, but subsequent rules may take effect. Any other
+expansion failure causes the entire rewriting operation to be abandoned, and an
+entry written to the panic log.
+
+
+.section Rewriting flags
+There are three different kinds of flag that may appear on rewriting rules:
+.numberpars $.
+Flags that specify which headers and envelope addresses to rewrite: E, F, T, b,
+c, f, h, r, s, t.
+.nextp
+A flag that specifies rewriting at SMTP time: S.
+.nextp
+Flags that control the rewriting process: Q, q, R, w.
+.endp
+For rules that are part of the \headers@_rewrite\ generic transport option,
+E, F, T, and S are not permitted.
+
+
+.section Flags specifying which headers and envelope addresses to rewrite
+.index rewriting||flags
+If none of the following flag letters, nor the `S' flag (see section
+~~SECTrewriteS) are present, a main rewriting rule applies to all headers and
+to both the sender and recipient fields of the envelope, whereas a
+transport-time rewriting rule just applies to all headers. Otherwise, the
+rewriting rule is skipped unless the relevant addresses are being processed.
+.display
+E $rm{rewrite all envelope fields}
+F $rm{rewrite the envelope From field}
+T $rm{rewrite the envelope To field}
+b $rm{rewrite the ::Bcc:: header}
+c $rm{rewrite the ::Cc:: header}
+f $rm{rewrite the ::From:: header}
+h $rm{rewrite all headers}
+r $rm{rewrite the ::Reply-To:: header}
+s $rm{rewrite the ::Sender:: header}
+t $rm{rewrite the ::To:: header}
+.endd
+You should be particularly careful about rewriting ::Sender:: headers, and
+restrict this to special known cases in your own domains.
+
+.section The SMTP-time rewriting flag
+.rset SECTrewriteS "~~chapter.~~section"
+.index SMTP||rewriting malformed addresses
+.index \\RCPT\\||rewriting argument of
+.index \\MAIL\\||rewriting argument of
+The rewrite flag `S' specifies a rewrite of incoming envelope addresses at SMTP
+time, as soon as an address is received in a \\MAIL\\ or \\RCPT\\ command, and
+before any other processing; even before syntax checking. The pattern is
+required to be a regular expression, and it is matched against the whole of the
+data for the command, including any surrounding angle brackets.
+
+This form of rewrite rule allows for the handling of addresses that are not
+compliant with RFCs 2821 and 2822 (for example, `bang paths' in batched SMTP
+input). Because the input is not required to be a syntactically valid address,
+the variables \$local@_part$\ and \$domain$\ are not available during the
+expansion of the replacement string. The result of rewriting replaces the
+original address in the \\MAIL\\ or \\RCPT\\ command.
+
+.section Flags controlling the rewriting process
+There are four flags which control the way the rewriting process works. These
+take effect only when a rule is invoked, that is, when the address is of the
+correct type (matches the flags) and matches the pattern:
+.numberpars $.
+If the `Q' flag is set on a rule, the rewritten address is permitted to be an
+unqualified local part. It is qualified with \qualify@_recipient\. In the
+absence of `Q' the rewritten address must always include a domain.
+.nextp
+If the `q' flag is set on a rule, no further rewriting rules are considered,
+even if no rewriting actually takes place because of a `fail' in the expansion.
+The `q' flag is not effective if the address is of the wrong type (does not
+match the flags) or does not match the pattern.
+.nextp
+The `R' flag causes a successful rewriting rule to be re-applied to the new
+address, up to ten times. It can be combined with the `q' flag, to stop
+rewriting once it fails to match (after at least one successful rewrite).
+.nextp
+.index rewriting||whole addresses
+When an address in a header is rewritten, the rewriting normally applies only
+to the working part of the address, with any comments and RFC 2822 `phrase'
+left unchanged. For example, rewriting might change
+.display asis
+From: Ford Prefect <fp42@restaurant.hitch.fict.example>
+.endd
+into
+.display asis
+From: Ford Prefect <prefectf@hitch.fict.example>
+.endd
+Sometimes there is a need to replace the whole address item, and this can be
+done by adding the flag letter `w' to a rule. If this is set on a rule that
+causes an address in a header line to be rewritten, the entire address is
+replaced, not just the working part. The replacement must be a complete RFC
+2822 address, including the angle brackets if necessary. If text outside angle
+brackets contains a character whose value is greater than 126 or less than 32
+(except for tab), the text is encoded according to RFC 2047.
+The character set is taken from \headers@_charset\, which defaults to
+ISO-8859-1.
+
+When the `w' flag is set on a rule that causes an envelope address to be
+rewritten, all but the working part of the replacement address is discarded.
+.endp
+
+.section Rewriting examples
+Here is an example of the two common rewriting paradigms:
+.display asis
+*@*.hitch.fict.example $1@hitch.fict.example
+*@hitch.fict.example ${lookup{$1}dbm{/etc/realnames}\
+ {$value}fail}@hitch.fict.example bctfrF
+.endd
+Note the use of `fail' in the lookup expansion in the second rule, forcing
+the string expansion to fail if the lookup does not succeed. In this context it
+has the effect of leaving the original address unchanged, but Exim goes on to
+consider subsequent rewriting rules, if any, because the `q' flag is not
+present in that rule. An alternative to `fail' would be to supply \$1$\
+explicitly, which would cause the rewritten address to be the same as before,
+at the cost of a small bit of processing. Not supplying either of these is an
+error, since the rewritten address would then contain no local part.
+
+The first example above replaces the domain with a superior, more general
+domain. This may not be desirable for certain local parts. If the rule
+.display asis
+root@*.hitch.fict.example *
+.endd
+were inserted before the first rule, rewriting would be suppressed for the
+local part \*root*\ at any domain ending in \*hitch.fict.example*\.
+
+Rewriting can be made conditional on a number of tests, by making use of
+\${if$\ in the expansion item. For example, to apply a rewriting rule only to
+messages that originate outside the local host:
+.display asis
+*@*.hitch.fict.example "${if !eq {$sender_host_address}{}\
+ {$1@hitch.fict.example}fail}"
+.endd
+The replacement string is quoted in this example because it contains white
+space.
+
+.index rewriting||bang paths
+.index bang paths||rewriting
+Exim does not handle addresses in the form of `bang paths'. If it sees such an
+address it treats it as an unqualified local part which it qualifies with the
+local qualification domain (if the source of the message is local or if the
+remote host is permitted to send unqualified addresses). Rewriting can
+sometimes be used to handle simple bang paths with a fixed number of
+components. For example, the rule
+.display asis
+\N^([^!]+)!(.*)@your.domain.example$\N $2@$1
+.endd
+rewrites a two-component bang path \*host.name!user*\ as the domain address
+\*user@@host.name*\. However, there is a security implication in using this as
+a global rewriting rule for envelope addresses. It can provide a backdoor
+method for using your system as a relay, because the incoming addresses appear
+to be local. If the bang path addresses are received via SMTP, it is safer to
+use the `S' flag to rewrite them as they are received, so that relay checking
+can be done on the rewritten addresses.
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Retry configuration
+.set runningfoot "retry configuration"
+.rset CHAPretry ~~chapter
+.index retry||configuration, description of
+.index configuration file||retry section
+The `retry' section of the run time configuration file contains a list of retry
+rules which control how often Exim tries to deliver messages that cannot be
+delivered at the first attempt. If there are no retry rules, temporary errors
+are treated as permanent. The \-brt-\ command line option can be used to test
+which retry rule will be used for a given address or domain.
+
+The most common cause of retries is temporary failure to deliver to a remote
+host because the host is down, or inaccessible because of a network problem.
+Exim's retry processing in this case is applied on a per-host (strictly, per IP
+address) basis, not on a per-message basis. Thus, if one message has recently
+been delayed, delivery of a new message to the same host is not immediately
+tried, but waits for the host's retry time to arrive. If the \retry@_defer\ log
+selector is set, the message
+.index retry||time not reached
+`retry time not reached' is written to the main log whenever a delivery is
+skipped for this reason. Section ~~SECToutSMTPerr contains more details of the
+handling of errors during remote deliveries.
+
+Retry processing applies to routing as well as to delivering, except as covered
+in the next paragraph. The retry rules do not distinguish between these
+actions. It is not possible, for example, to specify different behaviour for
+failures to route the domain \*snark.fict.example*\ and failures to deliver to
+the host \*snark.fict.example*\. I didn't think anyone would ever need this
+added complication, so did not implement it. However, although they share the
+same retry rule, the actual retry times for routing and transporting a given
+domain are maintained independently.
+
+When a delivery is not part of a queue run (typically an immediate delivery on
+receipt of a message), the routers are always run, and local deliveries are
+always attempted, even if retry times are set for them. This makes for better
+behaviour if one particular message is causing problems (for example, causing
+quota overflow, or provoking an error in a filter file). If such a delivery
+suffers a temporary failure, the retry data is updated as normal, and
+subsequent delivery attempts from queue runs occur only when the retry time for
+the local address is reached.
+
+
+.section Retry rules
+.index retry||rules
+Each retry rule occupies one line and consists of three parts, separated by
+white space: a pattern, an error name, and a list of retry parameters. The
+pattern must be enclosed in double quotes if it contains white space. The rules
+are searched in order until one is found whose pattern matches the failing host
+or address.
+
+The pattern is any single item that may appear in an address list (see section
+~~SECTaddresslist). It is in fact processed as a one-item address list, which
+means that it is expanded before being tested against the address that has
+been delayed. Address list processing treats a plain domain name as if it were
+preceded by `*@@', which makes it possible for many retry rules to start with
+just a domain. For example,
+.display asis
+lookingglass.fict.example * F,24h,30m;
+.endd
+provides a rule for any address in the \*lookingglass.fict.example*\ domain,
+whereas
+.display asis
+alice@lookingglass.fict.example * F,24h,30m;
+.endd
+applies only to temporary failures involving the local part \alice\.
+In practice, almost all rules start with a domain name pattern without a local
+part.
+
+.index regular expressions||in retry rules
+\**Warning**\: If you use a regular expression in a routing rule, it must match
+a complete address, not just a domain, because that is how regular expressions
+work in address lists.
+.display
+^@\Nxyz@\d+@\.abc@\.example@$@\N * G,1h,10m,2 \Wrong\
+^@\N[^@@]+@@xyz@\d+@\.abc@\.example@$@\N * G,1h,10m,2 \Right\
+.endd
+
+
+.section Choosing which retry rule to use
+When Exim is looking for a retry rule after a routing attempt has failed (for
+example, after a DNS timeout), each line in the retry configuration is tested
+against the complete address only if \retry__use@_local@_part\ is set for the
+router. Otherwise, only the domain is used, except when matching against a
+regular expression, when the local part of the address is replaced with `*'. A
+domain on its own can match a domain pattern, or a pattern that starts with
+`*@@'. By default, \retry@_use@_local@_part\ is true for routers where
+\check@_local@_user\ is true, and false for other routers.
+
+Similarly, when Exim is looking for a retry rule after a local delivery has
+failed (for example, after a mailbox full error), each line in the retry
+configuration is tested against the complete address only if
+\retry@_use@_local@_part\ is set for the transport (it defaults true for all
+local transports).
+
+.em
+When Exim is looking for a retry rule after a remote delivery attempt has
+failed, what happens depends on the type of failure. After a 4\*xx*\ SMTP
+response for a recipient address, the whole address is used when searching the
+retry rules. The rule that is found is used to create a retry time for the
+failing address.
+
+For a temporary error that is not related to an individual address,
+.nem
+(for example, a connection timeout), each line in the retry configuration is
+checked twice. First, the name of the remote host is used as a domain name
+(preceded by `*@@' when matching a regular expression). If this does not match
+the line, the domain from the email address is tried in a similar fashion. For
+example, suppose the MX records for \*a.b.c.example*\ are
+.display asis
+a.b.c.example MX 5 x.y.z.example
+ MX 6 p.q.r.example
+ MX 7 m.n.o.example
+.endd
+and the retry rules are
+.display asis
+p.q.r.example * F,24h,30m;
+a.b.c.example * F,4d,45m;
+.endd
+and a delivery to the host \*x.y.z.example*\ fails. The first rule matches
+neither the host nor the domain, so Exim looks at the second rule. This does
+not match the host, but it does match the domain, so it is used to calculate
+the retry time for the host \*x.y.z.example*\. Meanwhile, Exim tries to deliver
+to \*p.q.r.example*\. If this fails, the first retry rule is used, because it
+matches the host.
+
+In other words, failures to deliver to host \*p.q.r.example*\ use the first
+rule to determine retry times, but for all the other hosts for the domain
+\*a.b.c.example*\, the second rule is used. The second rule is also used if
+routing to \*a.b.c.example*\ suffers a temporary failure.
+
+.section Retry rules for specific errors
+.index retry||specific errors, specifying
+The second field in a retry rule is the name of a particular error, or an
+asterisk, which matches any error. The errors that can be tested for are:
+.numberpars " "
+\*auth@_failed*\: authentication failed when trying to send to a host in the
+\hosts@_require@_auth\ list in an \%smtp%\ transport
+.nextp
+\*refused@_MX*\: connection refused from a host obtained from an MX record
+.nextp
+\*refused@_A*\: connection refused from a host not obtained from an MX record
+.nextp
+\*refused*\: any connection refusal
+.nextp
+\*timeout@_connect@_MX*\: connection timeout from a host obtained from an MX
+record
+.nextp
+\*timeout@_connect@_A*\: connection timeout from a host not obtained from an MX
+record
+.nextp
+\*timeout@_connect*\: any connection timeout
+.nextp
+\*timeout@_MX*\: any timeout from a host obtained from an MX
+record
+.nextp
+\*timeout@_A*\: any timeout from a host not obtained from an MX
+record
+.nextp
+\*timeout*\: any timeout
+.nextp
+\*quota*\: quota exceeded in local delivery by \%appendfile%\
+.nextp
+.index quota||error testing in retry rule
+.index retry||quota error testing
+\*quota@_*\<<time>>: quota exceeded in local delivery, and the mailbox has not
+been read for <<time>>. For example, \*quota@_4d*\ applies to a quota error
+when the mailbox has not been read for four days.
+
+.em
+.index mailbox||time of last read
+\**Warning**\: It is not always possible to determine a `time of last read' for
+a mailbox:
+.numberpars $.
+If the mailbox is a single file, the time of last access is used.
+.nextp
+.index maildir format||time of last read
+For a maildir delivery, the time of last modification of the \(new)\
+subdirectory is used. As the mailbox is over quota, no new files will be
+created in the \(new)\ subdirectory, so any change is assumed to be the result
+of an MUA moving a new message to the \(cur)\ directory when it is first read.
+.nextp
+For other kinds of multi-file delivery, the time of last read cannot be
+obtained, and so a retry rule that uses this type of error field is never
+matched.
+.endp
+.nem
+.endp
+The quota errors apply both to system-enforced quotas and to Exim's own quota
+mechanism in the \%appendfile%\ transport. The \*quota*\ error also applies
+when a local delivery is deferred because a partition is full (the \\ENOSPC\\
+error).
+
+
+.section Retry rule parameters
+.index retry||parameters in rules
+The third field in a retry rule is a sequence of retry parameter sets,
+separated by semicolons. Each set consists of
+.display
+<<letter>>,<<cutoff time>>,<<arguments>>
+.endd
+The letter identifies the algorithm for computing a new retry time; the cutoff
+time is the time beyond which this algorithm no longer applies, and the
+arguments vary the algorithm's action. The cutoff time is measured from the
+time that the first failure for the domain (combined with the local part if
+relevant) was detected, not from the time the message was received.
+.index retry||algorithms
+The available algorithms are:
+.numberpars $.
+\*F*\: retry at fixed intervals. There is a single time parameter specifying the
+interval.
+.nextp
+\*G*\: retry at geometrically increasing intervals. The first argument specifies
+a starting value for the interval, and the second a multiplier, which is used
+to increase the size of the interval at each retry.
+.endp
+When computing the next retry time, the algorithm definitions are scanned in
+order until one whose cutoff time has not yet passed is reached. This is then
+used to compute a new retry time that is later than the current time. In the
+case of fixed interval retries, this simply means adding the interval to the
+current time. For geometrically increasing intervals, retry intervals are
+computed from the rule's parameters until one that is greater than the previous
+interval is found. The main configuration variable
+.index limit||retry interval
+.index retry||interval, maximum
+.index \retry@_interval@_max\
+\retry@_interval@_max\ limits the maximum interval between retries.
+
+A single remote domain may have a number of hosts associated with it, and each
+host may have more than one IP address. Retry algorithms are selected on the
+basis of the domain name, but are applied to each IP address independently. If,
+for example, a host has two IP addresses and one is unusable, Exim will
+generate retry times for it and will not try to use it until its next retry
+time comes. Thus the good IP address is likely to be tried first most of the
+time.
+
+.index hints database||use for retrying
+Retry times are hints rather than promises. Exim does not make any attempt to
+run deliveries exactly at the computed times. Instead, a queue runner process
+starts delivery processes for delayed messages periodically, and these attempt
+new deliveries only for those addresses that have passed their next retry time.
+If a new message arrives for a deferred address, an immediate delivery attempt
+occurs only if the address has passed its retry time. In the absence of new
+messages, the minimum time between retries is the interval between queue runner
+processes. There is not much point in setting retry times of five minutes if
+your queue runners happen only once an hour, unless there are a significant
+number of incoming messages (which might be the case on a system that is
+sending everything to a smart host, for example).
+
+The data in the retry hints database can be inspected by using the
+\*exim@_dumpdb*\ or \*exim@_fixdb*\ utility programs (see chapter ~~CHAPutils). The
+latter utility can also be used to change the data. The \*exinext*\ utility
+script can be used to find out what the next retry times are for the hosts
+associated with a particular mail domain, and also for local deliveries that
+have been deferred.
+
+.section Retry rule examples
+Here are some example retry rules:
+.display asis
+alice@wonderland.fict.example quota_5d F,7d,3h
+wonderland.fict.example quota_5d
+wonderland.fict.example * F,1h,15m; G,2d,1h,2;
+lookingglass.fict.example * F,24h,30m;
+* refused_A F,2h,20m;
+* * F,2h,15m; G,16h,1h,1.5; F,5d,8h
+.endd
+The first rule sets up special handling for mail to
+\*alice@@wonderland.fict.example*\ when there is an over-quota error and the
+mailbox has not been read for at least 5 days. Retries continue every three
+hours for 7 days. The second rule handles over-quota errors for all other local
+parts at \*wonderland.fict.example*\; the absence of a local part has the same
+effect as supplying `$*$@@'. As no retry algorithms are supplied, messages that
+fail are bounced immediately if the mailbox has not been read for at least 5
+days.
+
+The third rule handles all other errors at \*wonderland.fict.example*\; retries
+happen every 15 minutes for an hour, then with geometrically increasing
+intervals until two days have passed since a delivery first failed. After the
+first hour there is a delay of one hour, then two hours, then four hours, and
+so on (this is a rather extreme example).
+
+The fourth rule controls retries for the domain \*lookingglass.fict.example*\.
+They happen every 30 minutes for 24 hours only. The remaining two rules handle
+all other domains, with special action for connection refusal from hosts that
+were not obtained from an MX record.
+
+The final rule in a retry configuration should always have asterisks in the
+first two fields so as to provide a general catch-all for any addresses that do
+not have their own special handling. This example tries every 15 minutes for 2
+hours, then with intervals starting at one hour and increasing by a factor of
+1.5 up to 16 hours, then every 8 hours up to 5 days.
+
+
+.section Timeout of retry data
+.index timeout||of retry data
+.index \retry@_data@_expire\
+.index hints database||data expiry
+.index retry||timeout of data
+Exim timestamps the data that it writes to its retry hints database. When it
+consults the data during a delivery it ignores any that is older than the value
+set in \retry@_data@_expire\ (default 7 days). If, for example, a host hasn't
+been tried for 7 days, Exim will try to deliver to it immediately a message
+arrives, and if that fails, it will calculate a retry time as if it were
+failing for the first time.
+
+This improves the behaviour for messages routed to rarely-used hosts such as MX
+backups. If such a host was down at one time, and happens to be down again when
+Exim tries a month later, using the old retry data would imply that it had been
+down all the time, which is not a justified assumption.
+
+If a host really is permanently dead, this behaviour causes a burst of retries
+every now and again, but only if messages routed to it are rare. It there is a
+message at least once every 7 days the retry data never expires.
+
+
+
+.section Long-term failures
+.index delivery||failure, long-term
+.index retry||after long-term failure
+Special processing happens when an email address has been failing for so long
+that the cutoff time for the last algorithm is reached. For example, using the
+default retry rule:
+.display asis
+* * F,2h,15m; G,16h,1h,1.5; F,4d,6h
+.endd
+the cutoff time is four days. Reaching the retry cutoff is independent of how
+long any specific message has been failing; it is the length of continuous
+failure for the recipient address that counts.
+
+When the cutoff time is reached for a local delivery, or for all the IP
+addresses associated with a remote delivery, a subsequent delivery failure
+causes Exim to give up on the address, and a bounce message is generated.
+In order to cater for new messages that use the failing address, a next retry
+time is still computed from the final algorithm, and is used as follows:
+
+For local deliveries, one delivery attempt is always made for any subsequent
+messages. If this delivery fails, the address fails immediately. The
+post-cutoff retry time is not used.
+
+If the delivery is remote, there are two possibilities, controlled by the
+.index \delay@_after@_cutoff\
+\delay@_after@_cutoff\ option of the \%smtp%\ transport. The option is true by
+default and in that case:
+.numberpars " "
+Until the post-cutoff retry time for one of the IP addresses is reached,
+the failing email address is bounced immediately, without a delivery attempt
+taking place. After that time, one new delivery attempt is made to those IP
+addresses that are past their retry times, and if that still fails, the address
+is bounced and new retry times are computed.
+.endp
+
+In other words, when all the hosts for a given email address have been failing
+for a long time, Exim bounces rather then defers until one of the hosts' retry
+times is reached. Then it tries once, and bounces if that attempt fails. This
+behaviour ensures that few resources are wasted in repeatedly trying to deliver
+to a broken destination, but if the host does recover, Exim will eventually
+notice.
+
+If \delay@_after@_cutoff\ is set false, Exim behaves differently. If all IP
+addresses are past their final cutoff time, Exim tries to deliver to those IP
+addresses that have not been tried since the message arrived. If there are
+no suitable IP addresses, or if they all fail, the address is bounced. In other
+words, it does not delay when a new message arrives, but tries the expired
+addresses immediately, unless they have been tried since the message arrived.
+If there is a continuous stream of messages for the failing domains, setting
+\delay@_after@_cutoff\ false means that there will be many more attempts to
+deliver to permanently failing IP addresses than when \delay@_after@_cutoff\ is
+true.
+
+.section Ultimate address timeout
+.index retry||ultimate address timeout
+An additional rule is needed to cope with cases where a host is intermittently
+available, or when a message has some attribute that prevents its delivery when
+others to the same address get through. In this situation, because some
+messages are successfully delivered, the `retry clock' for the address keeps
+getting restarted, and so a message could remain on the queue for ever. To
+prevent this, if a message has been on the queue for longer than the cutoff
+time of any applicable retry rule for a given address, a delivery is attempted
+for that address, even if it is not yet time, and if this delivery fails, the
+address is timed out. A new retry time is not computed in this case, so that
+other messages for the same address are considered immediately.
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter SMTP authentication
+.set runningfoot "SMTP authentication"
+.rset CHAPSMTPAUTH "~~chapter"
+.index SMTP||authentication configuration
+.index authentication
+The `authenticators' section of Exim's run time configuration is concerned with
+SMTP authentication. This facility is an extension to the SMTP protocol,
+described in RFC 2554, which allows a client SMTP host to authenticate itself
+to a server. This is a common way for a server to recognize clients that
+are permitted to use it as a relay. SMTP authentication is not of relevance to
+the transfer of mail between servers that have no managerial connection with
+each other.
+
+.index \\AUTH\\||description of
+Very briefly, the way SMTP authentication works is as follows:
+.numberpars $.
+The server advertises a number of authentication \*mechanisms*\ in response to
+the client's \\EHLO\\ command.
+.nextp
+The client issues an \\AUTH\\ command, naming a specific mechanism. The command
+may, optionally, contain some authentication data.
+.nextp
+The server may issue one or more \*challenges*\, to which the client must send
+appropriate responses. In simple authentication mechanisms, the challenges are
+just prompts for user names and passwords. The server does not have to issue
+any challenges -- in some mechanisms the relevant data may all be transmitted
+with the \\AUTH\\ command.
+.nextp
+The server either accepts or denies authentication.
+.nextp
+If authentication succeeds, the client may optionally make use of the \\AUTH\\
+option on the \\MAIL\\ command to pass an authenticated sender in subsequent
+mail transactions. Authentication lasts for the remainder of the SMTP
+connection.
+.nextp
+If authentication fails, the client may give up, or it may try a different
+authentication mechanism, or it may try transferring mail over the
+unauthenticated connection.
+.endp
+If you are setting up a client, and want to know which authentication
+mechanisms the server supports, you can use Telnet to connect to port 25 (the
+SMTP port) on the server, and issue an \\EHLO\\ command. The response to this
+includes the list of supported mechanisms. For example:
+.display
+@$ $cb{telnet server.example 25}
+Trying 192.168.34.25...
+Connected to server.example.
+Escape character is '@^]'.
+220 server.example ESMTP Exim 4.20 ...
+$cb{ehlo client.example}
+250-server.example Hello client.example [10.8.4.5]
+250-SIZE 52428800
+250-PIPELINING
+250-AUTH PLAIN
+250 HELP
+.endd
+The second-last line of this example output shows that the server supports
+authentication using the PLAIN mechanism. In Exim, the different authentication
+mechanisms are configured by specifying \*authenticator*\ drivers. Like the
+routers and transports, which authenticators are included in the binary is
+controlled by build-time definitions. The following are currently available,
+included by setting
+.display asis
+AUTH_CRAM_MD5=yes
+AUTH_PLAINTEXT=yes
+AUTH_SPA=yes
+.endd
+in \(Local/Makefile)\, respectively. The first of these supports the CRAM-MD5
+authentication mechanism (RFC 2195), and the second can be configured to
+support the PLAIN authentication mechanism (RFC 2595) or the LOGIN mechanism,
+which is not formally documented, but used by several MUAs. The third
+authenticator supports Microsoft's \*Secure Password Authentication*\
+mechanism.
+
+The authenticators are configured using the same syntax as other drivers (see
+section ~~SECTfordricon). If no authenticators are required, no authentication
+section need be present in the configuration file. Each authenticator can in
+principle have both server and client functions. When Exim is receiving SMTP
+mail, it is acting as a server; when it is sending out messages over SMTP, it
+is acting as a client. Authenticator configuration options are provided for use
+in both these circumstances.
+
+To make it clear which options apply to which situation, the prefixes
+\server@_\ and \client@_\ are used on option names that are specific to either
+the server or the client function, respectively. Server and client functions
+are disabled if none of their options are set. If an authenticator is to be
+used for both server and client functions, a single definition, using both sets
+of options, is required. For example:
+.display asis
+cram:
+ driver = cram_md5
+ public_name = CRAM-MD5
+ server_secret = ${if eq{$1}{ph10}{secret1}fail}
+ client_name = ph10
+ client_secret = secret2
+.endd
+The \server@_\ option is used when Exim is acting as a server, and the
+\client@_\ options when it is acting as a client.
+
+Descriptions of the individual authenticators are given in subsequent chapters.
+The remainder of this chapter covers the generic options for the
+authenticators, followed by general discussion of the way authentication works
+in Exim.
+
+
+.section Generic options for authenticators
+.index authentication||generic options
+
+.startconf
+.index options||generic, for authenticators
+
+.conf driver string unset
+This option must always be set. It specifies which of the available
+authenticators is to be used.
+
+.conf public@_name string unset
+This option specifies the name of the authentication mechanism that the driver
+implements, and by which it is known to the outside world. These names should
+contain only upper case letters, digits, underscores, and hyphens (RFC 2222),
+but Exim in fact matches them caselessly. If \public@_name\ is not set, it
+defaults to the driver's instance name.
+
+.conf server@_advertise@_condition string$**$ unset
+When a server is about to advertise an authentication mechanism, the condition
+is expanded. If it yields the empty string, `0', `no', or `false', the
+mechanism is not advertised.
+If the expansion fails, the mechanism is not advertised. If the failure was not
+forced, and was not caused by a lookup defer, the incident is logged.
+See section ~~SECTauthexiser below for further discussion.
+
+.conf server@_debug@_print string$**$ unset
+If this option is set and authentication debugging is enabled (see the \-d-\
+command line option), the string is expanded and included in the debugging
+output when the authenticator is run as a server. This can help with checking
+out the values of variables.
+If expansion of the string fails, the error message is written to the debugging
+output, and Exim carries on processing.
+
+.conf server@_set@_id string$**$ unset
+When an Exim server successfully authenticates a client, this string is
+expanded using data from the authentication, and preserved for any incoming
+messages in the variable \$authenticated@_id$\. It is also included in the log
+lines for incoming messages. For example, a user/password authenticator
+configuration might preserve the user name that was used to authenticate, and
+refer to it subsequently during delivery of the message.
+If expansion fails, the option is ignored.
+
+.conf server@_mail@_auth@_condition string$**$ unset
+This option allows a server to discard authenticated sender addresses supplied
+as part of \\MAIL\\ commands in SMTP connections that are authenticated by the
+driver on which \server__mail__auth@_condition\ is set. The option is not used
+as part of the authentication process; instead its (unexpanded) value is
+remembered for later use.
+How it is used is described in the following section.
+.endconf
+
+
+
+.section The AUTH parameter on MAIL commands
+.rset SECTauthparamail "~~chapter.~~section"
+.index authentication||sender, authenticated
+.index \\AUTH\\||on \\MAIL\\ command
+When a client supplied an \\AUTH=\\ item on a \\MAIL\\ command, Exim applies
+the following checks before accepting it as the authenticated sender of the
+message:
+.numberpars $.
+If the connection is not using extended SMTP (that is, \\HELO\\ was used rather
+than \\EHLO\\), the use of \\AUTH=\\ is a syntax error.
+.nextp
+If the value of the \\AUTH=\\ parameter is `@<@>', it is ignored.
+.nextp
+If \acl@_smtp@_mailauth\ is defined, the ACL it specifies is run. While it is
+running, the value of \$authenticated@_sender$\ is set to the value obtained
+from the \\AUTH=\\ parameter. If the ACL does not yield `accept', the value of
+\$authenticated@_sender$\ is deleted. The \acl@_smtp@_mailauth\ ACL may not
+return `drop' or `discard'. If it defers, a temporary error code (451) is given
+for the \\MAIL\\ command.
+.nextp
+If \acl@_smtp@_mailauth\ is not defined, the value of the \\AUTH=\\ parameter
+is accepted and placed in \$authenticated@_sender$\ only if the client has
+authenticated.
+.nextp
+If the \\AUTH=\\ value was accepted by either of the two previous rules, and
+the client has authenticated, and the authenticator has a setting for the
+\server@_mail@_auth@_condition\, the condition is checked at this point. The
+valued that was saved from the authenticator is expanded. If the expansion
+fails, or yields an empty string, `0', `no', or `false', the value of
+\$authenticated__sender$\ is deleted. If the expansion yields any other value,
+the value of \$authenticated@_sender$\ is retained and passed on with the
+message.
+.endp
+
+When \$authenticated@_sender$\ is set for a message, it is passed on to other
+hosts to which Exim authenticates as a client. Do not confuse this value with
+\$authenticated@_id$\, which is a string obtained from the authentication
+process, and which is not usually a complete email address.
+
+Whenever an \\AUTH=\\ value is ignored, the incident is logged. The ACL for
+\\MAIL\\, if defined, is run after \\AUTH=\\ is accepted or ignored. It can
+therefore make use of \$authenticated@_sender$\. The converse is not true: the
+value of \$sender@_address$\ is not yet set up when the \acl@_smtp@_mailauth\
+ACL is run.
+
+
+.section Authentication on an Exim server
+.rset SECTauthexiser "~~chapter.~~section"
+.index authentication||on an Exim server
+When Exim receives an \\EHLO\\ command, it advertises the public names of those
+authenticators that are configured as servers, subject to the following
+conditions:
+.numberpars $.
+The client host must match \auth@_advertise@_hosts\ (default $*$).
+.nextp
+It the \server@_advertise@_condition\ option is set, its expansion must not
+yield the empty string, `0', `no', or `false'.
+.endp
+The order in which the authenticators are defined controls the order in which
+the mechanisms are advertised.
+
+Some mail clients (for example, some versions of Netscape) require the user to
+provide a name and password for authentication whenever \\AUTH\\ is advertised,
+even though authentication may not in fact be needed (for example, Exim may be
+set up to allow unconditional relaying from the client by an IP address check).
+You can make such clients more friendly by not advertising \\AUTH\\ to them.
+For example, if clients on the 10.9.8.0/24 network are permitted (by the ACL
+that runs for \\RCPT\\) to relay without authentication, you should set
+.display asis
+auth_advertise_hosts = ! 10.9.8.0/24
+.endd
+so that no authentication mechanisms are advertised to them.
+
+The \server@_advertise@_condition\ controls the advertisement of individual
+authentication mechanisms. For example, it can be used to restrict the
+advertisement of a patricular mechanism to encrypted connections, by a setting
+such as:
+.display asis
+server_advertise_condition = ${if eq{$tls_cipher}{}{no}{yes}}
+.endd
+If the session is encrypted, \$tls@_cipher$\ is not empty, and so the expansion
+yields `yes', which allows the advertisement to happen.
+
+When an Exim server receives an \\AUTH\\ command from a client, it rejects it
+immediately if \\AUTH\\ was not advertised in response to an earlier \\EHLO\\
+command. This is the case if
+.numberpars $.
+The client host does not match \auth@_advertise@_hosts\; or
+.nextp
+No authenticators are configured with server options; or
+.nextp
+Expansion of \server@_advertise@_condition\ blocked the advertising of all the
+server authenticators.
+.endp
+
+Otherwise, Exim runs the ACL specified by \acl@_smtp@_auth\ in order
+to decide whether to accept the command. If \acl@_smtp@_auth\ is not set,
+\\AUTH\\ is accepted from any client host.
+
+If \\AUTH\\ is not rejected by the ACL, Exim searches its configuration for a
+server authentication mechanism that was advertised in response to \\EHLO\\ and
+that matches the one named in the \\AUTH\\ command. If it finds one, it runs
+the appropriate authentication protocol, and authentication either succeeds or
+fails. If there is no matching advertised mechanism, the \\AUTH\\ command is
+rejected with a 504 error.
+
+When a message is received from an authenticated host, the value of
+\$received@_protocol$\ is set to `asmtp' instead of `esmtp', and
+\$sender@_host@_authenticated$\ contains the name (not the public name) of the
+authenticator driver that successfully authenticated the client from which the
+message was received. This variable is empty if there was no successful
+authentication.
+
+
+
+.section Testing server authentication
+.index authentication||testing a server
+.index \\AUTH\\||testing a server
+.index base64 encoding||creating authentication test data
+Exim's \-bh-\ option can be useful for testing server authentication
+configurations. The data for the \\AUTH\\ command has to be sent using base64
+encoding. A quick way to produce such data for testing is the following Perl
+script:
+.display asis
+use MIME::Base64;
+printf ("%s", encode_base64(eval "\"$ARGV[0]\""));
+.endd
+.index binary zero||in authentication data
+This interprets its argument as a Perl string, and then encodes it. The
+interpretation as a Perl string allows binary zeros, which are required for
+some kinds of authentication, to be included in the data. For example, a
+command line to run this script on such data might be
+.display asis
+encode '\0user\0password'
+.endd
+Note the use of single quotes to prevent the shell interpreting the
+backslashes, so that they can be interpreted by Perl to specify characters
+whose code value is zero.
+
+\**Warning 1**\: If either of the user or password strings starts with an octal
+digit, you must use three zeros instead of one after the leading backslash. If
+you do not, the octal digit that starts your string will be incorrectly
+interpreted as part of the code for the first character.
+
+\**Warning 2**\: If there are characters in the strings that Perl interprets
+specially, you must use a Perl escape to prevent them being misinterpreted. For
+example, a command such as
+.display asis
+encode '\0user@domain.com\0pas$$word'
+.endd
+gives an incorrect answer because of the unescaped `@@' and `@$' characters.
+
+If you have the \mimencode\ command installed, another way to do produce
+base64-encoded strings is to run the command
+.display asis
+echo -e -n `\0user\0password' | mimencode
+.endd
+The \-e-\ option of \echo\ enables the interpretation of backslash escapes in
+the argument, and the \-n-\ option specifies no newline at the end of its
+output. However, not all versions of \echo\ recognize these options, so you
+should check your version before relying on this suggestion.
+
+
+.section Authentication by an Exim client
+.index authentication||on an Exim client
+The \%smtp%\ transport has two options called \hosts@_require@_auth\ and
+\hosts@_try@_auth\. When the \%smtp%\ transport connects to a server that
+announces support for authentication, and the host matches an entry in either
+of these options, Exim (as a client) tries to authenticate as follows:
+.numberpars $.
+For each authenticator that is configured as a client, it searches the
+authentication mechanisms announced by the server for one whose name
+matches the public name of the authenticator.
+.nextp
+When it finds one that matches, it runs the authenticator's client code.
+The variables \$host$\ and \$host@_address$\ are available for any string
+expansions that the client might do. They are set to the server's name and
+IP address. If any expansion is forced to fail, the authentication attempt
+is abandoned,
+and Exim moves on to the next authenticator.
+Otherwise an expansion failure causes delivery to be
+deferred.
+.nextp
+If the result of the authentication attempt is a temporary error or a timeout,
+Exim abandons trying to send the message to the host for the moment. It will
+try again later. If there are any backup hosts available, they are tried in the
+usual way.
+.nextp
+If the response to authentication is a permanent error (5xx code), Exim carries
+on searching the list of authenticators and tries another one if possible. If
+all authentication attempts give permanent errors, or if there are no attempts
+because no mechanisms match
+(or option expansions force failure),
+what happens depends on whether the host matches \hosts@_require@_auth\ or
+\hosts@_try@_auth\. In the first case, a temporary error is generated, and
+delivery is deferred. The error can be detected in the retry rules, and thereby
+turned into a permanent error if you wish. In the second case, Exim tries to
+deliver the message unauthenticated.
+.endp
+.index \\AUTH\\||on \\MAIL\\ command
+When Exim has authenticated itself to a remote server, it adds the \\AUTH\\
+parameter to the \\MAIL\\ commands it sends, if it has an authenticated sender
+for the message.
+If the message came from a remote host, the authenticated sender is the one
+that was receiving on an incoming \\MAIL\\ command, provided that the incoming
+connection was authenticated and the \server@_mail@_auth\ condition allowed the
+authenticated sender to be retained. If a local process calls Exim to send a
+message, the sender address that is built from the login name and
+\qualify@_domain\ is treated as authenticated. However, if the
+\authenticated@_sender\ option is set on the \%smtp%\ transport, it overrides
+the authenticated sender that was received with the message.
+
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The plaintext authenticator
+.rset CHAPplaintext "~~chapter"
+.set runningfoot "plaintext authenticator"
+.index \%plaintext%\ authenticator
+.index authenticators||\%plaintext%\
+The \%plaintext%\ authenticator can be configured to support the PLAIN and
+LOGIN authentication mechanisms, both of which transfer authentication data as
+plain (unencrypted) text (though base64 encoded). The use of plain text is a
+security risk. If you use one of these mechanisms without also making use of
+SMTP encryption (see chapter ~~CHAPTLS) you should not use the same passwords
+for SMTP connections as you do for login accounts.
+
+.section Using plaintext in a server
+When running as a server, \%plaintext%\ performs the authentication test by
+expanding a string. It has the following options:
+
+.startconf
+.index options||\%plaintext%\ authenticator (server)
+
+.conf server@_prompts string$**$ unset
+The contents of this option, after expansion, must be a colon-separated list of
+prompt strings. If expansion fails, a temporary authentication rejection is
+given.
+
+.conf server@_condition string$**$ unset
+This option must be set in order to configure the driver as a server. Its use
+is described below.
+
+.endconf
+
+.index \\AUTH\\||in \%plaintext%\ authenticator
+.index binary zero||in \%plaintext%\ authenticator
+.index numerical variables (\$1$\, \$2$\, etc)||in \%plaintext%\ authenticator
+.index base64 encoding||in \%plaintext%\ authenticator
+The data sent by the client with the \\AUTH\\ command, or in response to
+subsequent prompts, is base64 encoded, and so may contain any byte values
+when decoded. If any data is supplied with the command, it is treated as a
+list of strings, separated by NULs (binary zeros), which are placed in the
+expansion variables \$1$\, \$2$\, etc. If there are more strings in
+\server@_prompts\ than the number of strings supplied with the \\AUTH\\
+command, the remaining prompts are used to obtain more data. Each response from
+the client may be a list of NUL-separated strings.
+
+Once a sufficient number of data strings have been received,
+\server@_condition\ is expanded.
+If the expansion is forced to fail, authentication fails. Any other expansion
+failure causes a temporary error code to be returned.
+If the result of a successful expansion is an empty string, `0', `no', or
+`false', authentication fails. If the result of the expansion is `1', `yes', or
+`true', authentication succeeds and the generic \server@_set@_id\ option is
+expanded and saved in \$authenticated@_id$\. For any other result, a temporary
+error code is returned, with the expanded string as the error text.
+
+\**Warning**\: If you use a lookup in the expansion to find the user's
+password, be sure to make the authentication fail if the user is unknown.
+There are good and bad examples at the end of the next section.
+
+
+.section The PLAIN authentication mechanism
+.index PLAIN authentication mechanism
+.index authentication||PLAIN mechanism
+.index binary zero||in \%plaintext%\ authenticator
+The PLAIN authentication mechanism (RFC 2595) specifies that three strings be
+sent as one item of data (that is, one combined string containing two NUL
+separators). The data is sent either as part of the \\AUTH\\ command, or
+subsequently in response to an empty prompt from the server.
+
+The second and third strings are a user name and a corresponding password.
+Using a single fixed user name and password as an example, this could be
+configured as follows:
+.display asis
+fixed_plain:
+ driver = plaintext
+ public_name = PLAIN
+ server_prompts = :
+ server_condition = \
+ ${if and {{eq{$2}{username}}{eq{$3}{mysecret}}}{yes}{no}}
+ server_set_id = $2
+.endd
+The \server@_prompts\ setting specifies a single, empty prompt (empty items at
+the end of a string list are ignored). If all the data comes as part of the
+\\AUTH\\ command, as is commonly the case, the prompt is not used. This
+authenticator is advertised in the response to \\EHLO\\ as
+.display asis
+250-AUTH PLAIN
+.endd
+and a client host can authenticate itself by sending the command
+.display asis
+AUTH PLAIN AHVzZXJuYW1lAG15c2VjcmV0
+.endd
+As this contains three strings (more than the number of prompts), no further
+data is required from the client. Alternatively, the client may just send
+.display asis
+AUTH PLAIN
+.endd
+to initiate authentication, in which case the server replies with an empty
+prompt. The client must respond with the combined data string.
+
+.em
+The data string is base64 encoded, as required by the RFC. This example,
+when decoded, is \"<<NUL>>username<<NUL>>mysecret"\, where <<NUL>> represents a
+zero byte. This is split up into three strings, the first of which is empty.
+The \server@_condition\ option in the authenticator checks that the second two
+are \"username"\ and \"mysecret"\ respectively.
+
+Having just one fixed user name and password, as in this example, is not very
+realistic, though for a small organization with only a handful of
+authenticating clients it could make sense.
+.nem
+
+A more sophisticated instance of this authenticator could use the user name in
+\$2$\ to look up a password in a file or database, and maybe do an encrypted
+comparison (see \crypteq\ in chapter ~~CHAPexpand). Here is a example of this
+approach, where the passwords are looked up in a DBM file. \**Warning**\: This
+is an incorrect example:
+.display asis
+server_condition = \
+ ${if eq{$3}{${lookup{$2}dbm{/etc/authpwd}}}{yes}{no}}
+.endd
+The expansion uses the user name (\$2$\) as the key to look up a password,
+which it then compares to the supplied password (\$3$\). Why is this example
+incorrect? It works fine for existing users, but consider what happens if a
+non-existent user name is given. The lookup fails, but as no success/failure
+strings are given for the lookup, it yields an empty string. Thus, to defeat
+the authentication, all a client has to do is to supply a non-existent user
+name and an empty password. The correct way of writing this test is:
+.display asis
+server_condition = ${lookup{$2}dbm{/etc/authpwd}\
+ {${if eq{$value}{$3}{yes}{no}}}{no}}
+.endd
+In this case, if the lookup succeeds, the result is checked; if the lookup
+fails, authentication fails. If \crypteq\ is being used instead of \eq\, the
+first example is in fact safe, because \crypteq\ always fails if its second
+argument is empty. However, the second way of writing the test makes the logic
+clearer.
+
+
+.section The LOGIN authentication mechanism
+.index LOGIN authentication mechanism
+.index authentication||LOGIN mechanism
+The LOGIN authentication mechanism is not documented in any RFC, but is in use
+in a number of programs. No data is sent with the \\AUTH\\ command. Instead, a
+user name and password are supplied separately, in response to prompts. The
+plaintext authenticator can be configured to support this as in this example:
+.display asis
+fixed_login:
+ driver = plaintext
+ public_name = LOGIN
+ server_prompts = User Name : Password
+ server_condition = \
+ ${if and {{eq{$1}{username}}{eq{$2}{mysecret}}}{yes}{no}}
+ server_set_id = $1
+.endd
+Because of the way plaintext operates, this authenticator accepts data supplied
+with the \\AUTH\\ command (in contravention of the specification of LOGIN), but
+if the client does not supply it (as is the case for LOGIN clients), the prompt
+strings are used to obtain two data items.
+
+Some clients are very particular about the precise text of the prompts. For
+example, Outlook Express is reported to recognize only `Username:' and
+`Password:'. Here is an example of a LOGIN authenticator which uses those
+strings, and which uses the \ldapauth\ expansion condition to check the user
+name and password by binding to an LDAP server:
+.display asis
+login:
+ driver = plaintext
+ public_name = LOGIN
+ server_prompts = Username:: : Password::
+ server_condition = ${if ldapauth \
+.newline
+ {user="cn=${quote_ldap_dn:$1},ou=people,o=example.org" \
+ pass=${quote:$2} \
+.newline
+ ldap://ldap.example.org/}{yes}{no}}
+ server_set_id = uid=$1,ou=people,o=example.org
+.endd
+Note the use of the \quote@_ldap@_dn\ operator to correctly quote the DN for
+authentication. However, the basic \quote\ operator, rather than any of the
+LDAP quoting operators, is the correct one to use for the password, because
+quoting is needed only to make the password conform to the Exim syntax. At the
+LDAP level, the password is an uninterpreted string.
+
+
+.section Support for different kinds of authentication
+A number of string expansion features are provided for the purpose of
+interfacing to different ways of user authentication. These include checking
+traditionally encrypted passwords from \(/etc/passwd)\ (or equivalent), PAM,
+Radius, \ldapauth\, and \*pwcheck*\. For details see section ~~SECTexpcond.
+
+
+
+.section Using plaintext in a client
+The \%plaintext%\ authenticator has just one client option:
+
+.startconf
+.index options||\%plaintext%\ authenticator (client)
+
+.conf client@_send string$**$ unset
+The string is a colon-separated list of authentication data strings. Each
+string is independently expanded before being sent to the server. The first
+string is sent with the \\AUTH\\ command; any more strings are sent in response
+to prompts from the server.
+
+\**Note**\: you cannot use expansion to create multiple strings, because
+splitting takes priority and happens first.
+
+Because the PLAIN authentication mechanism requires NUL (binary zero) bytes in
+the data, further processing is applied to each string before it is sent. If
+there are any single circumflex characters in the string, they are converted to
+NULs. Should an actual circumflex be required as data, it must be doubled in
+the string.
+
+.endconf
+
+This is an example of a client configuration that implements the PLAIN
+authentication mechanism with a fixed user name and password:
+.display asis
+fixed_plain:
+ driver = plaintext
+ public_name = PLAIN
+ client_send = ^username^mysecret
+.endd
+The lack of colons means that the entire text is sent with the \\AUTH\\
+command, with the circumflex characters converted to NULs. A similar example
+that uses the LOGIN mechanism is:
+.display asis
+fixed_login:
+ driver = plaintext
+ public_name = LOGIN
+ client_send = : username : mysecret
+.endd
+The initial colon means that the first string is empty, so no data is sent with
+the \\AUTH\\ command itself. The remaining strings are sent in response to
+prompts.
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The cram@_md5 authenticator
+.set runningfoot "cram@_md5 authenticator"
+.index \%cram@_md5%\ authenticator
+.index authenticators||\%cram@_md5%\
+.index CRAM-MD5 authentication mechanism
+.index authentication||CRAM-MD5 mechanism
+The CRAM-MD5 authentication mechanism is described in RFC 2195. The server
+sends a challenge string to the client, and the response consists of a user
+name and the CRAM-MD5 digest of the challenge string combined with a secret
+string (password) which is known to both server and client. Thus, the secret
+is not sent over the network as plain text, which makes this authenticator more
+secure than \%plaintext%\. However, the downside is that the secret has to be
+available in plain text at either end.
+
+.section Using cram@_md5 as a server
+This authenticator has one server option, which must be set to configure the
+authenticator as a server:
+
+.startconf
+.index options||\%cram@_md5%\ authenticator (server)
+
+.conf server@_secret string$**$ unset
+.index numerical variables (\$1$\, \$2$\, etc)||in \%cram@_md5%\ authenticator
+When the server receives the client's response, the user name is placed in
+the expansion variable \$1$\, and \server@_secret\ is expanded to obtain the
+password for that user. The server then computes the CRAM-MD5 digest that the
+client should have sent, and checks that it received the correct string. If the
+expansion of \server@_secret\ is forced to fail, authentication fails. If the
+expansion fails for some other reason, a temporary error code is returned to
+the client.
+
+.endconf
+
+For example, the following authenticator checks that the user name given by the
+client is `ph10', and if so, uses `secret' as the password. For any other user
+name, authentication fails.
+.display asis
+fixed_cram:
+ driver = cram_md5
+ public_name = CRAM-MD5
+ server_secret = ${if eq{$1}{ph10}{secret}fail}
+ server_set_id = $1
+.endd
+If authentication succeeds, the setting of \server@_set@_id\ preserves the user
+name in \$authenticated@_id$\.
+A more tyical configuration might look up the secret string in a file, using
+the user name as the key. For example:
+.display asis
+lookup_cram:
+ driver = cram_md5
+ public_name = CRAM-MD5
+ server_secret = ${lookup{$1}lsearch{/etc/authpwd}{$value}fail}
+ server_set_id = $1
+.endd
+Note that this expansion explicitly forces failure if the lookup fails
+because \$1$\ contains an unknown user name.
+
+.section Using cram@_md5 as a client
+When used as a client, the \%cram@_md5%\ authenticator has two options:
+
+.startconf
+.index options||\%cram@_md5%\ authenticator (client)
+
+.conf client@_name string$**$ "the primary host name"
+This string is expanded, and the result used as the user name data when
+computing the response to the server's challenge.
+
+.conf client@_secret string$**$ unset
+This option must be set for the authenticator to work as a client. Its value is
+expanded and the result used as the secret string when computing the response.
+
+.endconf
+
+Different user names and secrets can be used for different servers by referring
+to \$host$\ or \$host@_address$\ in the options.
+
+Forced failure of either expansion string is treated as an indication that this
+authenticator is not prepared to handle this case. Exim moves on to the next
+configured client authenticator. Any other expansion failure causes Exim to
+give up trying to send the message to the current server.
+
+A simple example configuration of a \%cram@_md5%\ authenticator, using fixed
+strings, is:
+.display asis
+fixed_cram:
+ driver = cram_md5
+ public_name = CRAM-MD5
+ client_name = ph10
+ client_secret = secret
+.endd
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The spa authenticator
+.set runningfoot "spa authenticator"
+.index \%spa%\ authenticator
+.index authenticators||\%spa%\
+.index authentication||Microsoft Secure Password
+.index authentication||NTLM
+.index Microsoft Secure Password Authentication
+.index NTLM authentication
+The \%spa%\ authenticator provides client support for Microsoft's \*Secure
+Password Authentication*\ mechanism,
+which is also sometimes known as NTLM (NT LanMan). The code for client side of
+this authenticator was contributed by Marc Prud'hommeaux, and much of it is
+taken from the Samba project (\?http://www.samba.org?\). The code for the
+server side was subsequently contributed by Tom Kistner.
+
+The mechanism works as follows:
+.numberpars $.
+After the \\AUTH\\ command has been accepted, the client sends an SPA
+authentication request based on the user name and optional domain.
+.nextp
+The server sends back a challenge.
+.nextp
+The client builds a challenge response which makes use of the user's password
+and sends it to the server, which then accepts or rejects it.
+.endp
+Encryption is used to protect the password in transit.
+
+
+.section Using spa as a server
+The \%spa%\ authenticator has just one server option:
+
+.startconf
+.index options||\%spa%\ authenticator (server)
+
+.conf server@_password string$**$ unset
+.index numerical variables (\$1$\, \$2$\, etc)||in \%spa%\ authenticator
+This option is expanded, and the result must be the cleartext password for the
+authenticating user, whose name is at this point in \$1$\. For example:
+.display asis
+spa:
+ driver = spa
+ public_name = NTLM
+ server_password = ${lookup{$1}lsearch{/etc/exim/spa_clearpass}}
+.endd
+If the expansion is forced to fail, authentication fails. Any other expansion
+failure causes a temporary error code to be returned.
+
+.endconf
+
+
+
+.section Using spa as a client
+The \%spa%\ authenticator has the following client options:
+
+.startconf
+.index options||\%spa%\ authenticator (client)
+
+.conf client@_domain string$**$ unset
+This option specifies an optional domain for the authentication.
+
+.conf client@_password string$**$ unset
+This option specifies the user's password, and must be set.
+
+.conf client@_username string$**$ unset
+This option specifies the user name, and must be set.
+
+.endconf
+
+Here is an example of a configuration of this authenticator for use with the
+mail servers at \*msn.com*\:
+.display asis
+msn:
+ driver = spa
+ public_name = MSN
+ client_username = msn/msn_username
+ client_password = msn_plaintext_password
+ client_domain = DOMAIN_OR_UNSET
+.endd
+
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Encrypted SMTP connections using TLS/SSL
+.set runningfoot "TLS encryption"
+.rset CHAPTLS "~~chapter"
+.index encryption||on SMTP connection
+.index SMTP||encryption
+.index TLS||on SMTP connection
+.index OpenSSL
+.index GnuTLS
+.em
+Support for TLS (Transport Layer Security), formerly known as SSL (Secure
+Sockets Layer), is implemented by making use of the OpenSSL library or the
+GnuTLS library (Exim requires GnuTLS release 1.0 or later).
+.nem
+There is no cryptographic code in the Exim distribution itself for implementing
+TLS. In order to use this feature you must install OpenSSL or GnuTLS, and then
+build a version of Exim that includes TLS support (see section
+~~SECTinctlsssl). You also need to understand the basic concepts of encryption
+at a managerial level, and in particular, the way that public keys, private
+keys, and certificates are used.
+
+RFC 2487 defines how SMTP connections can make use of encryption. Once a
+connection is established, the client issues a \\STARTTLS\\ command. If the
+server accepts this, the client and the server negotiate an encryption
+mechanism. If the negotiation succeeds, the data that subsequently passes
+between them is encrypted.
+
+Exim also has support for legacy clients that do not use the \\STARTTLS\\
+mechanism. Instead, they connect to a different port on the server (usually
+called the `ssmtp' port), and expect to negotiate a TLS session as soon as the
+connection to the server is established. The \-tls-on-connect-\ command line
+option can be used to run an Exim server in this way from \*inetd*\, and it can
+also be used to run a special daemon that operates in this manner (use \-oX-\
+to specify the port).
+
+Exim's ACLs can detect whether the current SMTP session is encrypted or not,
+and if so, what cipher suite is in use, whether the client supplied a
+certificate, and whether or not that certificate was verified. This makes it
+possible for an Exim server to deny or accept certain commands based on the
+encryption state.
+
+\**Warning**\: certain types of firewall and certain anti-virus products can
+disrupt TLS connections. You need to turn off SMTP scanning for these products
+in order to get TLS to work.
+
+
+.section OpenSSL vs GnuTLS
+.index TLS||OpenSSL \*vs*\ GnuTLS
+.rset SECTopenvsgnu "~~chapter.~~section"
+The first TLS support in Exim was implemented using OpenSSL. Support for GnuTLS
+followed later, when the first versions of GnuTLS were released. To build Exim
+to use GnuTLS, you need to set
+.display asis
+USE_GNUTLS=yes
+.endd
+in Local/Makefile, in addition to
+.display asis
+SUPPORT_TLS=yes
+.endd
+You must also set \\TLS@_LIBS\\ and \\TLS@_INCLUDE\\ appropriately, so that the
+include files and libraries for GnuTLS can be found.
+
+There are some differences in usage when using GnuTLS instead of OpenSSL:
+.numberpars $.
+.em
+The \tls@_verify@_certificates\ option must contain the name of a file, not the
+name of a directory (for OpenSSL it can be either).
+.nem
+.nextp
+The \tls@_dhparam\ option is ignored, because early versions of GnuTLS had no
+facility for varying its Diffie-Hellman parameters. I understand that this has
+changed, but Exim has not been updated to provide this facility.
+.nextp
+GnuTLS uses RSA and D-H parameters that take a substantial amount of
+time to compute. It is unreasonable to re-compute them for every TLS
+session. Therefore, Exim keeps this data in a file in its spool
+directory, called \(gnutls-params)\. The file is owned by the Exim user and is
+readable only by its owner. Every Exim process that start up GnuTLS reads the
+RSA and D-H parameters from this file. If the file does not exist, the first
+Exim process that needs it computes the data and writes it to a temporary file
+which is renamed once it is complete. It does not matter if several Exim
+processes do this simultaneously (apart from wasting a few resources). Once a
+file is in place, new Exim processes immediately start using it.
+
+For maximum security, the parameters that are stored in this file should be
+recalculated periodically, the frequency depending on your paranoia level.
+Arranging this is easy; just delete the file when you want new values to be
+computed.
+.nextp
+.em
+Distinguished Name (DN) strings reported by the OpenSSL library use a slash for
+separating fields; GnuTLS uses commas, in accordance with RFC 2253. This
+affects the value of the \$tls@_peerdn$\ variable.
+.nem
+.nextp
+OpenSSL identifies cipher suites using hyphens as separators, for example:
+DES-CBC3-SHA. GnuTLS uses underscores, for example: RSA@_ARCFOUR@_SHA. What is
+more, OpenSSL complains if underscores are present in a cipher list. To make
+life simpler, Exim changes underscores to hyhens for OpenSSL and hyphens to
+underscores for GnuTLS when processing lists of cipher suites in the
+.em
+\tls@_require@_ciphers\ options (the global option and the \%smtp%\ transport
+option).
+.nem
+.nextp
+.em
+The \tls@_require@_ciphers\ options operate differently, as described in the
+following section.
+.nem
+.endp
+
+.em
+.section Requiring specific ciphers in OpenSSL and GnuTLS
+.rset SECTreqciphsslgnu "~~chapter.~~section"
+.index TLS||requiring specific ciphers
+.index \tls@_require@_ciphers\||OpenSSL \*vs*\ GnuTLS
+This section documents the different ways the \tls@_require@_ciphers\ options
+(the global option and the \%smtp%\ transport option) operate in OpenSSL and
+GnuTLS.
+
+There is a function in the OpenSSL library that can be passed a list of
+cipher suites before the cipher negotiation takes place. This specifies which
+ciphers are acceptable. The list is colon separated and may contain names like
+DES-CBC3-SHA. Exim passes the expanded value of \tls@_require@_ciphers\
+directly to this function call. The following quotation from
+the OpenSSL documentation specifies what forms of item are allowed in the
+cipher string:
+.numberpars $.
+It can consist of a single cipher suite such as RC4-SHA.
+.nextp
+It can represent a list of cipher suites containing a certain algorithm,
+or cipher suites of a certain type. For example SHA1 represents all
+ciphers suites using the digest algorithm SHA1 and SSLv3 represents all
+SSL v3 algorithms.
+.nextp
+Lists of cipher suites can be combined in a single cipher string using
+the + character. This is used as a logical and operation. For example
+SHA1+DES represents all cipher suites containing the SHA1 and the DES
+algorithms.
+.nextp
+Each cipher string can be optionally preceded by the characters \"!"\, \"-"\ or
+\"+"\.
+.numberpars " "
+If \"!"\ is used then the ciphers are permanently deleted from the list. The
+ciphers deleted can never reappear in the list even if they are explicitly
+stated.
+.nextp
+If \"-"\ is used then the ciphers are deleted from the list, but some or all
+of the ciphers can be added again by later options.
+.nextp
+If \"+"\ is used then the ciphers are moved to the end of the list. This
+option doesn't add any new ciphers it just moves matching existing ones.
+.nextp
+If none of these characters is present then the string is just interpreted as a
+list of ciphers to be appended to the current preference list. If the list
+includes any ciphers already present they will be ignored: that is, they will
+not moved to the end of the list.
+.endp
+.endp
+
+The GnuTLS library does not have a combined function like OpenSSL. Instead,
+it allows the caller to specify separate lists of key-exchange methods,
+main cipher algorithms, and MAC algorithms. Unfortunately, these lists are
+numerical, and the library does not have a function for turning names into
+numbers. Consequently, the list of recognized names has to be built into
+the application.
+
+At present, Exim permits only the list of main cipher algorithms to be
+changed. The \tls@_require@_ciphers\ option is in the same format as for
+OpenSSL. Exim searches each item for the name of available algorithm. For
+example, if the list contains RSA@_ARCFOUR@_SHA then ARCFOUR is recognized.
+
+The cipher algorithms list starts out with a default set of algorithms. If
+the first item in \tls@_require@_ciphers\ does \*not*\ start with an
+exclamation mark, all the default items are deleted. Thus, only those specified
+can be used. If the first item in \tls@_require@_ciphers\ \*does*\ start with
+an exclamation mark, the defaults are left on the list.
+
+Then, any item that starts with an exclamation mark causes the relevent
+algorithms to be removed from the list, and any item that does not start
+with an exclamation mark causes the relevant algorithms to be added to the
+list. Thus,
+.display asis
+tls_require_ciphers = !RSA_ARCFOUR_SHA
+.endd
+allows all the defaults except those that use ARCFOUR, whereas
+.display asis
+tls_require_ciphers = AES : 3DES
+.endd
+allows only cipher suites that use AES and 3DES. The currently recognized
+algorithms are: ARCFOUR@_128, ARCFOUR@_40, ARCFOUR (both of the preceding),
+AES@_256, AES@_128, AES (both of the preceding), and 3DES.
+
+Unrecognized algorithms are ignored. In a client, the order of the list
+specifies a preference order for the algorithms.
+.nem
+
+
+.section Configuring an Exim server to use TLS
+.index TLS||configuring an Exim server
+When Exim has been built with TLS support, it advertises the availability of
+the \\STARTTLS\\ command to client hosts that match \tls@_advertise@_hosts\,
+but not to any others. The default value of this option is unset, which means
+that \\STARTTLS\\ is not advertised at all. This default is chosen because you
+need to set some other options in order to make TLS avaliable, and also it is
+sensible for systems that want to use TLS only as a client.
+
+If a client issues a \\STARTTLS\\ command and there is some configuration
+problem in the server, the command is rejected with a 454 error. If the client
+persists in trying to issue SMTP commands, all except \\QUIT\\ are rejected
+with the error
+.display asis
+554 Security failure
+.endd
+If a \\STARTTLS\\ command is issued within an existing TLS session, it is
+rejected with a 554 error code.
+
+To enable TLS operations on a server, you must set \tls@_advertise@_hosts\ to
+match some hosts. You can, of course, set it to $*$ to match all hosts.
+However, this is not all you need to do. TLS sessions to a server won't work
+without some further configuration at the server end.
+
+It is rumoured that all existing clients that support TLS/SSL use RSA
+encryption. To make this work you need to set, in the server,
+.display asis
+tls_certificate = /some/file/name
+tls_privatekey = /some/file/name
+.endd
+The first file contains the server's X509 certificate, and the second contains
+the private key that goes with it. These files need to be readable by the Exim
+user, and must always be given as full path names. They can be the same file if
+both the certificate and the key are contained within it. If \tls@_privatekey\
+is not set, this is assumed to be the case. The certificate file may also
+contain intermediate certificates that need to be sent to the client to enable
+it to authenticate the server's certificate.
+
+If you do not understand about certificates and keys, please try to find a
+source of this background information, which is not Exim-specific. (There are a
+few comments below in section ~~SECTcerandall.)
+
+\**Note**\: These options do not apply when Exim is operating as a client --
+they apply only in the case of a server. For a client, you must set the options
+of the same name in an \%smtp%\ transport.
+
+With just these options, Exim will work as a server with clients such as
+Netscape. It does not require the client to have a certificate (but see below
+for how to insist on this). There is one other option that may be needed in
+other situations. If
+.display asis
+tls_dhparam = /some/file/name
+.endd
+is set, the SSL library is initialized for the use of Diffie-Hellman ciphers
+with the parameters contained in the file. This increases the set of cipher
+suites that the server supports. See the command
+.display asis
+openssl dhparam
+.endd
+for a way of generating this data.
+At present, \tls@_dhparam\ is used only when Exim is linked with OpenSSL. It is
+ignored if GnuTLS is being used.
+
+The strings supplied for these three options are expanded every time a client
+host connects. It is therefore possible to use different certificates and keys
+for different hosts, if you so wish, by making use of the client's IP address
+in \$sender@_host@_address$\ to control the expansion. If a string expansion is
+forced to fail, Exim behaves as if the option is not set.
+
+.index cipher||logging
+.index log||TLS cipher
+The variable \$tls@_cipher$\ is set to the cipher suite that was negotiated for
+an incoming TLS connection. It is included in the ::Received:: header of an
+incoming message (by default -- you can, of course, change this), and it is
+also included in the log line that records a message's arrival, keyed by `X=',
+unless the \tls@_cipher\ log selector is turned off.
+The \encrypted\ condition can be used to test for specific cipher suites in
+ACLs.
+
+The ACLs that run for subsequent SMTP commands can check the name of the cipher
+suite and vary their actions accordingly. The cipher suite names are those used
+by OpenSSL. These may differ from the names used elsewhere. For example,
+OpenSSL uses the name DES-CBC3-SHA for the cipher suite which in other contexts
+is known as TLS@_RSA@_WITH@_3DES@_EDE@_CBC@_SHA. Check the OpenSSL
+documentation for more details.
+
+
+.section Requesting and verifying client certificates
+.index certificate||verification of client
+.index TLS||client certificate verification
+If you want an Exim server to request a certificate when negotiating a TLS
+session with a client, you must set either \tls@_verify@_hosts\ or
+\tls@_try@_verify@_hosts\. You can, of course, set either of them to $*$ to
+apply to all TLS connections. For any host that matches one of these options,
+Exim requests a certificate as part of the setup of the TLS session. The
+contents of the certificate are verified by comparing it with a list of
+expected certificates. These must be available in a file or,
+.em
+for OpenSSL only (not GnuTLS), a directory, identified by
+\tls@_verify@_certificates\.
+.nem
+
+A file can contain multiple certificates, concatenated end to end. If a
+directory is used
+.em
+(OpenSSL only),
+.nem
+each certificate must be in a separate file, with a name (or a symbolic link)
+of the form <<hash>>.0, where <<hash>> is a hash value constructed from the
+certificate. You can compute the relevant hash by running the command
+.display asis
+openssl x509 -hash -noout -in /cert/file
+.endd
+where \(/cert/file)\ contains a single certificate.
+
+The difference between \tls@_verify@_hosts\ and \tls@_try@_verify@_hosts\ is
+what happens if the client does not supply a certificate, or if the certificate
+does not match any of the certificates in the collection named by
+\tls@_verify@_certificates\. If the client matches \tls@_verify@_hosts\, the
+attempt to set up a TLS session is aborted, and the incoming connection is
+dropped. If the client matches \tls@_try@_verify@_hosts\, the (encrypted) SMTP
+session continues. ACLs that run for subsequent SMTP commands can detect the
+fact that no certificate was verified, and vary their actions accordingly. For
+example, you can insist on a certificate before accepting a message for
+relaying, but not when the message is destined for local delivery.
+
+When a client supplies a certificate (whether it verifies or not), the value of
+the Distinguished Name of the certificate is made available in the variable
+\$tls@_peerdn$\ during subsequent processing of the message.
+.index log||distinguished name
+Because it is often a long text string, it is not included in the log line or
+::Received:: header by default. You can arrange for it to be logged, keyed by
+`DN=', by setting the \tls@_peerdn\ log selector, and you can use
+\received@_header@_text\ to change the ::Received:: header. When no certificate
+is supplied, \$tls@_peerdn$\ is empty.
+
+.em
+.section Revoked certificates
+.index TLS||revoked certificates
+.index revocation list
+.index certificate||revocation list
+Certificate issuing authorities issue Certificate Revocation Lists (CRLs) when
+certificates are revoked. If you have such a list, you can pass it to an Exim
+server using the global option called \tls@_crl\ and to an Exim client using an
+identically named option for the \%smtp%\ transport. In each case, the value of
+the option is expanded and must then be the name of a file that contains a CRL
+in PEM format.
+.nem
+
+.section Configuring an Exim client to use TLS
+.index cipher||logging
+.index log||TLS cipher
+.index log||distinguished name
+.index TLS||configuring an Exim client
+The \tls@_cipher\ and \tls@_peerdn\ log selectors apply to outgoing SMTP
+deliveries as well as to incoming, the latter one causing logging of the
+server certificate's DN. The remaining client configuration for TLS is all
+within the \%smtp%\ transport.
+
+It is not necessary to set any options to have TLS work in the \%smtp%\
+transport. If Exim is built with TLS support, and TLS is advertised by a
+server, the \%smtp%\ transport always tries to start a TLS session. However,
+this can be prevented by setting \hosts@_avoid@_tls\ (an option of the
+transport) to a list of server hosts for which TLS should not be used.
+
+If you do not want Exim to attempt to send messages unencrypted when an attempt
+to set up an encrypted connection fails in any way, you can set
+\hosts@_require@_tls\ to a list of hosts for which encryption is mandatory. For
+those hosts, delivery is always deferred if an encrypted connection cannot be
+set up. If there are any other hosts for the address, they are tried in the
+usual way.
+
+When the server host is not in \hosts@_require@_tls\, Exim may try to deliver
+the message unencrypted. It always does this if the response to \\STARTTLS\\ is
+a 5\*xx*\ code. For a temporary error code, or for a failure to negotiate a TLS
+session after a success response code, what happens is controlled by the
+\tls@_tempfail@_tryclear\ option of the \%smtp%\ transport. If it is false,
+delivery to this host is deferred, and other hosts (if available) are tried. If
+it is true, Exim attempts to deliver unencrypted after a 4\*xx*\ response to
+\\STARTTLS\\, and if \\STARTTLS\\ is accepted, but the subsequent TLS
+negotiation fails, Exim closes the current connection (because it is in an
+unknown state), opens a new one to the same host, and then tries the delivery
+unencrypted.
+
+
+The \tls@_certificate\ and \tls@_privatekey\ options of the \%smtp%\ transport
+provide the client with a certificate, which is passed to the server if it
+requests it. If the server is Exim, it will request a certificate only if
+\tls@_verify@_hosts\ or \tls@_try@_verify@_hosts\ matches the client.
+\**Note**\: these options must be set in the \%smtp%\ transport for Exim to use
+TLS when it is operating as a client. Exim does not assume that a server
+certificate (set by the global options of the same name) should also be used
+when operating as a client.
+
+If \tls@_verify@_certificates\ is set, it must name a file or,
+.em
+for OpenSSL only (not GnuTLS), a directory, that contains a collection of
+expected server certificates. The client verifies the server's certificate
+against this collection, taking into account any revoked certificates that are
+in the list defined by \tls@_crl\.
+.nem
+
+If
+\tls@_require@_ciphers\ is set on the \%smtp%\ transport, it must contain a
+list of permitted cipher suites. If either of these checks fails, delivery to
+the current host is abandoned, and the \%smtp%\ transport tries to deliver to
+alternative hosts, if any.
+
+All the TLS options in the \%smtp%\ transport are expanded before use, with
+\$host$\ and \$host@_address$\ containing the name and address of the server to
+which the client is connected. Forced failure of an expansion causes Exim to
+behave as if the relevant option were unset.
+
+
+.section Multiple messages on the same encrypted TCP/IP connection
+.rset SECTmulmessam "~~chapter.~~section"
+.index multiple SMTP deliveries with TLS
+.index TLS||multiple message deliveries
+Exim sends multiple messages down the same TCP/IP connection by starting up
+an entirely new delivery process for each message, passing the socket from
+one process to the next. This implementation does not fit well with the use
+of TLS, because there is quite a lot of state information associated with a TLS
+connection, not just a socket identification. Passing all the state information
+to a new process is not feasible. Consequently, Exim shuts down an existing TLS
+session before passing the socket to a new process. The new process may then
+try to start a new TLS session, and if successful, may try to re-authenticate
+if \\AUTH\\ is in use, before sending the next message.
+
+The RFC is not clear as to whether or not an SMTP session continues in clear
+after TLS has been shut down, or whether TLS may be restarted again later, as
+just described. However, if the server is Exim, this shutdown and
+reinitialization works. It is not known which (if any) other servers operate
+successfully if the client closes a TLS session and continues with unencrypted
+SMTP, but there are certainly some that do not work. For such servers, Exim
+should not pass the socket to another process, because the failure of the
+subsequent attempt to use it would cause Exim to record a temporary host error,
+and delay other deliveries to that host.
+
+To test for this case, Exim sends an \\EHLO\\ command to the server after
+closing down the TLS session. If this fails in any way, the connection is
+closed instead of being passed to a new delivery process, but no retry
+information is recorded.
+
+There is also a manual override; you can set \hosts@_nopass@_tls\ on the
+\%smtp%\ transport to match those hosts for which Exim should not pass
+connections to new processes if TLS has been used.
+
+
+
+.section Certificates and all that
+.rset SECTcerandall "~~chapter.~~section"
+.index certificate||references to discussion
+In order to understand fully how TLS works, you need to know about
+certificates, certificate signing, and certificate authorities. This is not the
+place to give a tutorial, especially as I do not know very much about it
+myself. Some helpful introduction can be found in the FAQ for the SSL addition
+to Apache, currently at
+.display rm
+\?http://www.modssl.org/docs/2.7/ssl@_faq.html@#ToC24?\
+.endd
+Other parts of the \*modssl*\ documentation are also helpful, and have
+links to further files.
+Eric Rescorla's book, \*SSL and TLS*\, published by Addison-Wesley (ISBN
+0-201-61598-3), contains both introductory and more in-depth descriptions.
+Some sample programs taken from the book are available from
+.display rm
+\?http://www.rtfm.com/openssl-examples/?\
+.endd
+
+.section Certificate chains
+The file named by \tls@_certificate\ may contain more than one
+certificate. This is useful in the case where the certificate that is being
+sent is validated by an intermediate certificate which the other end does
+not have. Multiple certificates must be in the correct order in the file.
+First the host's certificate itself, then the first intermediate
+certificate to validate the issuer of the host certificate, then the next
+intermediate certificate to validate the issuer of the first intermediate
+certificate, and so on, until finally (optionally) the root certificate.
+The root certificate must already be trusted by the recipient for
+validation to succeed, of course, but if it's not preinstalled, sending the
+root certificate along with the rest makes it available for the user to
+install if the receiving end is a client MUA that can interact with a user.
+
+.section Self-signed certificates
+.index certificate||self-signed
+You can create a self-signed certificate using the \*req*\ command provided
+with OpenSSL, like this:
+.display asis
+openssl req -x509 -newkey rsa:1024 -keyout file1 -out file2 \
+ -days 9999 -nodes
+.endd
+\(file1)\ and \(file2)\ can be the same file; the key and the certificate are
+delimited and so can be identified independently. The \-days-\ option
+specifies a period for which the certificate is valid. The \-nodes-\ option is
+important: if you do not set it, the key is encrypted with a passphrase
+that you are prompted for, and any use that is made of the key causes more
+prompting for the passphrase. This is not helpful if you are going to use
+this certificate and key in an MTA, where prompting is not possible.
+
+A self-signed certificate made in this way is sufficient for testing, and
+may be adequate for all your requirements if you are mainly interested in
+encrypting transfers, and not in secure identification.
+
+However, many clients require that the certificate presented by the server be a
+user (also called `leaf' or `site') certificate, and not a self-signed
+certificate. In this situation, the self-signed certificate described above
+must be installed on the client host as a trusted root \*certification
+authority*\ (CA), and the certificate used by Exim must be a user certificate
+signed with that self-signed certificate.
+
+For information on creating self-signed CA certificates and using them to sign
+user certificates, see the \*General implementation overview*\ chapter of the
+Open-source PKI book, available online at \?http://ospkibook.sourceforge.net/?\.
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Access control lists
+.set runningfoot "ACL"
+.rset CHAPACL "~~chapter"
+.index ~~ACL||description
+.index control of incoming mail
+.index message||controlling incoming
+.index policy control||access control lists
+Access Control Lists (ACLs) are defined in a separate section of the run time
+configuration file, headed by `begin acl'. Each ACL definition starts with a
+name, terminated by a colon. Here is a complete ACL section which contains just
+one very small ACL:
+.display asis
+begin acl
+
+small_acl:
+ accept hosts = one.host.only
+.endd
+You can have as many lists as you like in the ACL section, and the order in
+which they appear does not matter. The lists are self-terminating.
+
+The majority of ACLs are used to control Exim's behaviour when it receives
+certain SMTP commands. This applies both to incoming TCP/IP connections, and
+when a local process submits a message over a pipe (using the \-bs-\ option).
+The most common use is for controlling which recipients are accepted in
+incoming messages. In addition, you can also define an ACL that is used to
+check local non-SMTP messages. The default configuration file contains an
+example of a realistic ACL for checking \\RCPT\\ commands. This is discussed in
+chapter ~~CHAPdefconfil.
+
+.section Testing ACLs
+The \-bh-\ command line option provides a way of testing your ACL configuration
+locally by running a fake SMTP session with which you interact. The host
+\*relay-test.mail-abuse.org*\ provides a service for checking your relaying
+configuration (see section ~~SECTcheralcon for more details).
+
+
+.section Specifying when ACLs are used
+.index ~~ACL||options for specifying
+In order to cause an ACL to be used, you have to name it in one of the relevant
+options in the main part of the configuration. These options are:
+.index \\AUTH\\||ACL for
+.index \\DATA\\, ACL for
+.index \\ETRN\\||ACL for
+.index \\EXPN\\||ACL for
+.index \\HELO\\||ACL for
+.index \\EHLO\\||ACL for
+.index \\MAIL\\||ACL for
+.index \\RCPT\\||ACL for
+.index \\STARTTLS\\, ACL for
+.index \\VRFY\\||ACL for
+.display
+.tabs 20
+.if !~~sys.fancy
+.tabs 24
+.fi
+\acl@_not@_smtp\ $t $rm{ACL for non-SMTP messages}
+\acl@_smtp@_auth\ $t $rm{ACL for \\AUTH\\}
+\acl@_smtp@_connect\ $t $rm{ACL for start of SMTP connection}
+\acl@_smtp@_data\ $t $rm{ACL after \\DATA\\}
+\acl@_smtp@_etrn\ $t $rm{ACL for \\ETRN\\}
+\acl@_smtp@_expn\ $t $rm{ACL for \\EXPN\\}
+\acl@_smtp@_helo\ $t $rm{ACL for \\HELO\\ or \\EHLO\\}
+\acl@_smtp@_mail\ $t $rm{ACL for \\MAIL\\}
+.newline
+\acl@_smtp@_mailauth\ $t $rm{ACL for the \\AUTH\\ parameter of \\MAIL\\}
+.newline
+\acl@_smtp@_rcpt\ $t $rm{ACL for \\RCPT\\}
+\acl@_smtp@_starttls\ $t $rm{ACL for \\STARTTLS\\}
+\acl@_smtp@_vrfy\ $t $rm{ACL for \\VRFY\\}
+.endd
+For example, if you set
+.display asis
+acl_smtp_rcpt = small_acl
+.endd
+the little ACL defined above is used whenever Exim receives a \\RCPT\\ command
+in an SMTP dialogue. The majority of policy tests on incoming messages can be
+done when \\RCPT\\ commands arrive. A rejection of \\RCPT\\ should cause the
+sending MTA to give up on the recipient address contained in the \\RCPT\\
+command, whereas rejection at other times may cause the client MTA to keep on
+trying to deliver the message. It is therefore recommended that you do as much
+testing as possible at \\RCPT\\ time.
+
+However, you cannot test the contents of the message, for example, to verify
+addresses in the headers, at \\RCPT\\ time. Such tests have to appear in the
+ACL that is run after the message has been received, before the final response
+to the \\DATA\\ command is sent. This is the ACL specified by
+\acl@_smtp@_data\. At this time, it is no longer possible to reject individual
+recipients. An error response should reject the entire message. Unfortunately,
+it is known that some MTAs do not treat hard (5$it{xx}) errors correctly at
+this point -- they keep the message on their queues and try again later, but
+that is their problem, though it does waste some of your resources.
+
+The ACL test specified by \acl@_smtp@_connect\ happens after the test specified
+by \host__reject__connection\ (which is now an anomaly) and any TCP Wrappers
+testing (if configured).
+
+The non-SMTP ACL applies to all non-interactive incoming messages, that is, it
+applies to batch SMTP as well as to non-SMTP messages. (Batch SMTP is not
+really SMTP.) This ACL is run just before the \*local@_scan()*\ function. Any
+kind of rejection is treated as permanent, because there is no way of sending a
+temporary error for these kinds of message. Many of the ACL conditions (for
+example, host tests, and tests on the state of the SMTP connection such as
+encryption and authentication) are not relevant and are forbidden in this ACL.
+
+
+.section ACL return codes
+.index ~~ACL||return codes
+The result of running an ACL is either `accept' or `deny', or, if some test
+cannot be completed (for example, if a database is down), `defer'. These
+results cause 2$it{xx}, 5$it{xx}, and 4$it{xx} return codes, respectively, to
+be used in the SMTP dialogue. A fourth return, `error', occurs when there is an
+error such as invalid syntax in the ACL. This also causes a 4$it{xx} return
+code.
+
+The ACLs that are relevant to message reception may also return `discard'. This
+has the effect of `accept', but causes either the entire message or an
+individual recipient address to be discarded. In other words, it is a
+blackholing facility. Use it with great care.
+
+If the ACL for \\MAIL\\ returns `discard', all recipients are discarded, and no
+ACL is run for subsequent \\RCPT\\ commands. The effect of `discard' in a
+\\RCPT\\ ACL is to discard just the one address. If there are no recipients
+left when the message's data is received, the \\DATA\\ ACL is not run. A
+`discard' return from the \\DATA\\ or the non-SMTP ACL discards all the
+remaining recipients.
+
+The \*local@_scan()*\ function is always run, even if there are no remaining
+recipients; it may create new recipients.
+
+
+.section Unset ACL options
+.index ~~ACL||unset options
+.em
+The default actions when any of the \acl@_$it{xxx}\ options are unset are not
+all the same. \**Note**\: These defaults apply only when the relevant ACL is
+not defined at all. For any defined ACL, the default action if control reaches
+the end of the ACL statements is `deny'.
+.nem
+
+For \acl@_not@_smtp\, \acl@_smtp@_auth\, \acl@_smtp@_connect\,
+\acl@_smtp@_data\, \acl@_smtp@_helo\, \acl__smtp__mail\, \acl@_smtp@_mailauth\,
+and \acl@_smtp@_starttls\, the
+.em
+action when the ACL is not defined is `accept'.
+
+For the others (\acl@_smtp@_etrn\, \acl@_smtp@_expn\, \acl@_smtp@_rcpt\, and
+\acl@_smtp@_vrfy\), the action when the ACL is not defined is `deny'.
+.nem
+This means that \acl@_smtp@_rcpt\ must be defined in order to receive any
+messages over an SMTP connection. For an example, see the ACL in the default
+configuration file.
+
+
+
+.section Data for message ACLs
+.index ~~ACL||data for message ACL
+When an ACL for \\MAIL\\, \\RCPT\\, or \\DATA\\ is being run, the variables
+that contain information about the host and the message's sender (for example,
+\$sender@_host@_address$\ and \$sender@_address$\) are set, and can be used in
+ACL statements. In the case of \\RCPT\\ (but not \\MAIL\\ or \\DATA\\),
+\$domain$\ and \$local@_part$\ are set from the argument address.
+
+When an ACL for the \\AUTH\\ parameter of \\MAIL\\ is being run, the variables
+that contain information about the host are set, but \$sender@_address$\ is not
+yet set.
+
+The \$message@_size$\ variable is set to the value of the \\SIZE\\ parameter on
+the \\MAIL\\ command at \\MAIL\\ and \\RCPT\\ time, or -1 if that parameter was
+not given.
+Its value is updated to the true message size by the time the ACL after
+\\DATA\\ is run.
+
+The \$rcpt@_count$\ variable increases by one for each \\RCPT\\ command
+received. The \$recipients@_count$\ variable increases by one each time a
+\\RCPT\\ command is accepted, so while an ACL for \\RCPT\\ is being processed,
+it contains the number of previously accepted recipients. At \\DATA\\ time,
+\$rcpt@_count$\ contains the total number of \\RCPT\\ commands, and
+\$recipients@_count$\ contains the total number of accepted recipients.
+
+
+
+.section Data for non-message ACLs
+.rset SECTdatfornon "~~chapter.~~section"
+.index ~~ACL||data for non-message ACL
+When an ACL for \\AUTH\\, \\ETRN\\, \\EXPN\\,
+\\STARTTLS\\,
+or \\VRFY\\ is being run, the remainder of the SMTP command line is placed in
+\$smtp@_command@_argument$\. This can be tested using a \condition\ condition.
+For example, here is an ACL for use with \\AUTH\\, which insists that either
+the session is encrypted, or the CRAM-MD5 authentication method is used. In
+other words, it does not permit authentication methods that use cleartext
+passwords on unencrypted connections.
+.display asis
+acl_check_auth:
+ accept encrypted = *
+ accept condition = ${if eq{${uc:$smtp_command_argument}}\
+ {CRAM-MD5}{yes}{no}}
+ deny message = TLS encryption or CRAM-MD5 required
+.endd
+(Another way of applying this restriction is to arrange for the authenticators
+that use cleartext passwords not to be advertised when the connection is not
+encrypted. You can use the generic \server@_advertise@_condition\ authenticator
+option to do this.)
+
+
+.section Use of the ACL selection options
+.index ~~ACL||specifying which to use
+The value of an \acl@_smtp@_$it{xxx}\ option is expanded before use, so you can
+use different ACLs in different circumstances, and in fact the resulting string
+does not have to be the name of a configured list. Having expanded the string,
+Exim searches for an ACL as follows:
+.numberpars $.
+If the string begins with a slash, Exim attempts to open the file and read
+its contents as an ACL.
+The lines are processed in the same way as lines in the Exim configuration
+file. In particular, continuation lines are supported, blank lines are ignored,
+as are lines whose first non-whitespace character is `@#'.
+If the file does not exist or cannot be read, an error occurs (typically
+causing a temporary failure of whatever caused the ACL to be run). For example:
+.display asis
+acl_smtp_data = /etc/acls/\
+ ${lookup{$sender_host_address}lsearch\
+ {/etc/acllist}{$value}{default}}
+.endd
+This looks up an ACL file to use on the basis of the host's IP address, falling
+back to a default if the lookup fails. If an ACL is successfully read from a
+file, it is retained in memory for the duration of the Exim process, so that it
+can be re-used without having to re-read the file.
+.nextp
+If the string does not start with a slash, and does not contain any spaces,
+Exim searches the ACL section of the configuration for a list whose name
+matches the string.
+.nextp
+If no named ACL is found, or if the string contains spaces, Exim parses
+the string as an inline ACL. This can save typing in cases where you just
+want to have something like
+.display asis
+acl_smtp_vrfy = accept
+.endd
+in order to allow free use of the \\VRFY\\ command.
+Such a string may contain newlines; it is processed in the same way as an ACL
+that is read from a file.
+.endp
+
+
+.section Format of an ACL
+.index ~~ACL||format of
+.index ~~ACL||verbs, definition of
+An individual ACL consists of a number of statements. Each statement starts
+with a verb, optionally followed by a number of conditions and other modifiers.
+If all the conditions are met, the verb is obeyed.
+The same condition may be used (with different arguments) more than once in the
+same statement. This provides a means of specifying an `and' conjunction
+between conditions. For example:
+.display asis
+deny dnslists = list1.example
+ dnslists = list2.example
+.endd
+
+If there are no conditions, the verb is always obeyed. What happens if any of
+the conditions are not met depends on the verb (and in one case, on a special
+modifier). Not all the conditions make sense at every testing point. For
+example, you cannot test a sender address in the ACL that is run for a \\VRFY\\
+command.
+
+The verbs are as follows:
+.numberpars $.
+\accept\: If all the conditions are met, the ACL returns `accept'. If any of
+the conditions are not met, what happens depends on whether \endpass\ appears
+among the conditions (for syntax see below). If the failing condition precedes
+\endpass\, control is passed to the next ACL statement; if it follows
+\endpass\, the ACL returns `deny'. Consider this statement, used to check a
+\\RCPT\\ command:
+.display asis
+accept domains = +local_domains
+ endpass
+ verify = recipient
+.endd
+If the recipient domain does not match the \domains\ condition, control passes
+to the next statement. If it does match, the recipient is verified, and the
+command is accepted if verification succeeds. However, if verification fails,
+the ACL yields `deny', because the failing condition is after \endpass\.
+.nextp
+\defer\: If all the conditions are met, the ACL returns `defer' which, in an
+SMTP session, causes a 4\*xx*\ response to be given. For a non-SMTP ACL,
+\defer\ is the same as \deny\, because there is no way of sending a temporary
+error. For a \\RCPT\\ command, \defer\ is much the same as using a
+\%redirect%\ router and \":defer:"\ while verifying, but the \defer\ verb can
+be used in any ACL, and even for a recipient it might be a simpler approach.
+.nextp
+\deny\: If all the conditions are met, the ACL returns `deny'. If any of the
+conditions are not met, control is passed to the next ACL statement. For
+example,
+.display asis
+deny dnslists = blackholes.mail-abuse.org
+.endd
+rejects commands from hosts that are on a DNS black list.
+.nextp
+\discard\: This verb behaves like \accept\, except that it returns `discard'
+from the ACL instead of `accept'. It is permitted only on ACLs that are
+concerned with receiving messages, and it causes recipients to be discarded.
+If the \log@_message\ modifier is set when \discard\ operates, its contents are
+added to the line that is automatically written to the log.
+
+If \discard\ is used in an ACL for \\RCPT\\, just the one recipient is
+discarded; if used for \\MAIL\\, \\DATA\\ or in the non-SMTP ACL, all the
+message's recipients are discarded. Recipients that are discarded before
+\\DATA\\ do not appear in the log line when the \log@_recipients\ log selector
+is set.
+.nextp
+\drop\: This verb behaves like \deny\, except that an SMTP connection is
+forcibly closed after the 5\*xx*\ error message has been sent. For example:
+.display asis
+drop message = I don't take more than 20 RCPTs
+ condition = ${if > {$rcpt_count}{20}{yes}{no}}
+.endd
+There is no difference between \deny\ and \drop\ for the connect-time ACL. The
+connection is always dropped after sending a 550 response.
+.nextp
+\require\: If all the conditions are met, control is passed to the next ACL
+statement. If any of the conditions are not met, the ACL returns `deny'. For
+example, when checking a \\RCPT\\ command,
+.display asis
+require verify = sender
+.endd
+passes control to subsequent statements only if the message's sender can be
+verified. Otherwise, it rejects the command.
+.nextp
+.em
+\warn\: If all the conditions are met, a header line is added to an incoming
+message and/or a line is written to Exim's main log. In all cases, control
+passes to the next ACL statement. The text of the added header line and the log
+line are specified by modifiers; if they are not present, a \warn\ verb just
+checks its conditions and obeys any `immediate' modifiers such as \set\ and
+\logwrite\.
+
+If any condition on a \warn\ statement cannot be completed (that is, there is
+some sort of defer), no header is added and the configured log line is not
+written. No further conditions or modifiers in the \warn\ statement are
+processed. The incident is logged, but the ACL continues to be processed, from
+the next statement onwards.
+
+When testing an incoming message, the \message\ modifier can be used on a
+\warn\ statement to add an extra header line,
+.nem
+as in this example:
+.display asis
+warn message = X-blacklisted-at: $dnslist_domain
+ dnslists = blackholes.mail-abuse.org : \
+ dialup.mail-abuse.org
+.endd
+If an identical header line is requested several times (provoked, for example,
+by multiple \\RCPT\\ commands), only one copy is actually added to the message.
+.em
+If the text of the \message\ modifier is not a valid header line,
+\"X-ACL-Warn:"\ is added to the front of it.
+.nem
+
+Header lines that are added by an ACL at \\MAIL\\ or \\RCPT\\ time are not
+visible in string expansions in the ACL for subsequent \\RCPT\\ commands.
+However they are visible in string expansions in the ACL that is run after
+\\DATA\\. If you want to preserve data between \\MAIL\\ and \\RCPT\\ ACLs, you
+can use ACL variables, as described in the next section. If a message is
+rejected after \\DATA\\, all added header lines are included in the entry that
+is written to the reject log.
+
+If a \message\ modifier is present on a \warn\ verb in an ACL that is not
+testing an incoming message, it is ignored, and the incident is logged.
+
+A \warn\ statement may use the \log@_message\ modifier to cause a line to be
+written to the main log when the statement's conditions are true.
+.em
+Just as for \message\, if an identical log line is requested several times in
+the same message, only one copy is actually written to the log. If you want to
+force duplicates to be written, use the \logwrite\ modifier instead.
+.nem
+
+When one of the \warn\ conditions is an address verification that fails, the
+text of the verification failure message is in \$acl@_verify@_message$\. If you
+want this logged, you must set it up explicitly. For example:
+.display asis
+warn !verify = sender
+ log_message = sender verify failed: $acl_verify_message
+.endd
+.endp
+
+At the end of each ACL there is an implicit unconditional \deny\.
+
+As you can see from the examples above, the conditions and modifiers are
+written one to a line, with the first one on the same line as the verb, and
+subsequent ones on following lines. If you have a very long condition, you can
+continue it onto several physical lines by the usual @\ continuation mechanism.
+It is conventional to align the conditions vertically.
+
+
+.section ACL variables
+.rset SECTaclvariables "~~chapter.~~section"
+.index ~~ACL||variables
+There are some special variables that can be set during ACL processing. They
+can be used to pass information between different ACLs, different
+invocations of the same ACL in the same SMTP connection, and between ACLs and
+the routers, transports, and filters that are used to deliver a message.
+There are two sets of these variables:
+.numberpars $.
+The values of \$acl@_c0$\ to \$acl@_c9$\ persist throughout an SMTP connection.
+They are never reset. Thus, a value that is set while receiving one message is
+still available when receiving the next message on the same SMTP connection.
+.nextp
+The values of \$acl@_m0$\ to \$acl@_m9$\ persist only while a message is being
+received. They are reset afterwards. They are also reset by \\MAIL\\, \\RSET\\,
+\\EHLO\\, \\HELO\\, and after starting up a TLS session.
+.endp
+When a message is accepted, the current values of all the ACL variables are
+preserved with the message and are subsequently made available at delivery
+time.
+
+The ACL variables are set by modifier called \set\. For example:
+.display asis
+accept hosts = whatever
+ set acl_m4 = some value
+.endd
+Note that the leading dollar sign is not used when naming a variable that is to
+be set. If you want to set a variable without taking any action, you can use a
+\warn\ verb without any other modifiers.
+
+
+.section Condition and modifier processing
+.index ~~ACL||conditions, processing
+.index ~~ACL||modifiers, processing
+An exclamation mark preceding a condition negates its result. For example,
+.display asis
+deny domains = *.dom.example
+ !verify = recipient
+.endd
+causes the ACL to return `deny' if the recipient domain ends in
+\*dom.example*\, but the recipient address cannot be verified.
+
+The arguments of conditions and modifiers are expanded. A forced failure
+of an expansion causes a condition to be ignored, that is, it behaves as if the
+condition is true. Consider these two statements:
+.display asis
+accept senders = ${lookup{$host_name}lsearch\
+ {/some/file}{$value}fail}
+accept senders = ${lookup{$host_name}lsearch\
+ {/some/file}{$value}{}}
+.endd
+Each attempts to look up a list of acceptable senders. If the lookup succeeds,
+the returned list is searched, but if the lookup fails the behaviour is
+different in the two cases. The \fail\ in the first statement causes the
+condition to be ignored, leaving no further conditions. The \accept\ verb
+therefore succeeds. The second statement, however, generates an empty list when
+the lookup fails. No sender can match an empty list, so the condition fails,
+and therefore the \accept\ also fails.
+
+ACL modifiers appear mixed in with conditions in ACL statements. Some of them
+specify actions that are taken as the conditions for a statement are checked;
+others specify text for messages that are used when access is denied or a
+warning is generated.
+
+The positioning of the modifiers in an ACL statement important, because the
+processing of a verb ceases as soon as its outcome is known. Only those
+modifiers that have already been encountered will take effect. For the \accept\
+and \require\ statements, this means that processing stops as soon as a false
+condition is met. For example, consider this use of the \message\ modifier:
+.display asis
+require message = Can't verify sender
+ verify = sender
+ message = Can't verify recipient
+ verify = recipient
+ message = This message cannot be used
+.endd
+If sender verification fails, Exim knows that the result of the statement is
+`deny', so it goes no further. The first \message\ modifier has been seen, so
+its text is used as the error message. If sender verification succeeds, but
+recipient verification fails, the second message is used. If recipient
+verification succeeds, the third message becomes `current', but is never used
+because there are no more conditions to cause failure.
+
+For the \deny\ verb, on the other hand, it is always the last \message\
+modifier that is used, because all the conditions must be true for rejection to
+happen. Specifying more than one \message\ modifier does not make sense, and
+the message can even be specified after all the conditions. For example:
+.display asis
+deny hosts = ...
+ !senders = *@my.domain.example
+ message = Invalid sender from client host
+.endd
+The `deny' result does not happen until the end of the statement is reached, by
+which time Exim has set up the message.
+
+
+.section ACL modifiers
+.rset SECTACLmodi "~~chapter.~~section"
+.index ~~ACL||modifiers, list of
+The ACL modifiers are as follows:
+
+.startitems
+
+.item "control = <<text>>"
+.index message||submission
+This modifier may appear only in ACLs for commands relating to incoming
+messages. It affects the subsequent processing of the message, provided that
+the message is eventually accepted.
+.em
+The text must be one of the words `freeze', `queue@_only', or `submission' (in
+the latter case, optionally followed by slash-delimited options). The first two
+cause the message to be frozen or just queued (without immediate delivery),
+respectively. The third tells Exim that this message is a submission from a
+local MUA. In this case, Exim applies certain fixups to the message if
+necessary. For example, it add a ::Date:: header line if one is not present.
+Details are given in chapter ~~CHAPmsgproc.
+.nem
+
+Once one of these controls is set, it remains set for the message. For example,
+if \control\ is used in a \\RCPT\\ ACL, it applies to the whole message, not
+just the individual recipient. The \control\ modifier can be used in several
+different ways. For example:
+.numberpars $.
+It can be at the end of an \accept\ statement:
+.display asis
+accept ...some conditions...
+ control = queue_only
+.endd
+In this case, the control is applied when this statement yields `accept'.
+.nextp
+It can be in the middle of an \accept\ statement:
+.display asis
+accept ...some conditions...
+ control = queue_only
+ ...some more conditions...
+.endd
+If the first set of conditions are true, the control is applied, even if the
+statement does not accept because one of the second set of conditions is false.
+In this case, some subsequent statement must yield `accept' for the control to
+be relevant.
+.nextp
+It can be used with \warn\ to apply the control, leaving the
+decision about accepting or denying to a subsequent verb. For
+example:
+.display asis
+warn ...some conditions...
+ control = freeze
+accept ...
+.endd
+.em
+This example of \warn\ does not contain \message\, \log@_message\, or
+\logwrite\, so it does not add anything to the message and does not write a log
+entry.
+.nem
+.endp
+
+.item "delay = <<time>>"
+.index \-bh-\ option
+This modifier causes Exim to wait for the time interval before proceeding. The
+time is given in the usual Exim notation. This modifier may appear in any ACL.
+The delay happens as soon as the modifier is processed.
+.em
+However, when testing Exim using the \-bh-\ option, the delay is not actually
+imposed (an appropriate message is output).
+.nem
+
+Like \control\, \delay\ can be used with \accept\ or
+\deny\, for example:
+.display asis
+deny ...some conditions...
+ delay = 30s
+.endd
+The delay happens if all the conditions are true, before the statement returns
+`deny'. Compare this with:
+.display asis
+deny delay = 30s
+ ...some conditions...
+.endd
+which waits for 30s before processing the conditions. The \delay\ modifier can
+also be used with \warn\ and together with \control\:
+.display
+warn ...some conditions...
+ delay = 2m
+ control = freeze
+accept ...
+.endd
+
+.item endpass
+This modifier, which has no argument, is recognized only in \accept\
+statements. It marks the boundary between the conditions whose failure causes
+control to pass to the next statement, and the conditions whose failure causes
+the ACL to return `deny'. See the description of \accept\ above.
+
+.item "log@_message = <<text>>"
+This modifier sets up a message that is used as part of the log message if the
+ACL denies access
+.em
+or a \warn\ statement's conditions are true.
+.nem
+For example:
+.display asis
+require log_message = wrong cipher suite $tls_cipher
+ encrypted = DES-CBC3-SHA
+.endd
+\log@_message\ adds to any underlying error message that may exist because of
+the condition failure. For example, while verifying a recipient address, a
+:::fail:: redirection might have already set up a message. Although the message
+is usually defined before the conditions to which it applies, the expansion
+does not happen until Exim decides that access is to be denied. This means that
+any variables that are set by the condition are available for inclusion in the
+message. For example, the \$dnslist@_<<xxx>>$\ variables are set after a DNS
+black list lookup succeeds. If the expansion of \log@_message\ fails, or if the
+result is an empty string, the modifier is ignored.
+
+If you want to use a \warn\ statement to log the result of an address
+verification, you can use \$acl__verify__message$\ to include the verification
+error message.
+
+.em
+If \log@_message\ is used with a \warn\ statement, `Warning:' is added to the
+start of the logged message. If the same warning log message is requested more
+than once while receiving a single email message, only one copy is actually
+logged. If you want to log multiple copies, use \logwrite\ instead of
+\log@_message\. In the absence of \log@_message\ and \logwrite\, nothing is
+logged for a succesful \warn\ statement.
+.nem
+
+If \log@_message\ is not present and there is no underlying error message (for
+example, from the failure of address verification), but \message\ is present,
+the \message\ text is used for logging rejections. However, if any text for
+logging contains newlines, only the first line is logged. In the absence of
+both \log@_message\ and \message\, a default built-in message is used for
+logging rejections.
+
+.item "logwrite = <<text>>"
+.index log||in ACL, immediate
+This modifier writes a message to a log file as soon as it is encountered when
+processing an ACL. (Compare \log@_message\, which,
+.em
+except in the case of \warn\,
+.nem
+is used only if the ACL statement denies access.) The \logwrite\ modifier can
+be used to log special incidents in ACLs. For example:
+.display
+accept <<some special conditions>>
+ control = freeze
+ logwrite = froze message because ...
+.endd
+By default, the message is written to the main log. However, it may begin
+with a colon, followed by a comma-separated list of log names, and then
+another colon, to specify exactly which logs are to be written. For
+example:
+.display asis
+logwrite = :main,reject: text for main and reject logs
+logwrite = :panic: text for panic log only
+.endd
+
+.item "message = <<text>>"
+This modifier sets up a text string that is expanded and used as an error
+message if the current statement causes the ACL to deny access. The expansion
+happens at the time Exim decides that access is to be denied, not at the time
+it processes \message\. If the expansion fails, or generates an empty string,
+the modifier is ignored. For ACLs that are triggered by SMTP commands, the
+message is returned as part of the SMTP error response.
+
+The \message\ modifier is also used with the \warn\ verb to specify one or more
+header lines to be added to an incoming message when all the conditions are
+true.
+If \message\ is used with \warn\ in an ACL that is not concerned with receiving
+a message, it has no effect.
+
+The text is literal; any quotes are taken as literals, but because the string
+is expanded, backslash escapes are processed anyway. If the message contains
+newlines, this gives rise to a multi-line SMTP response. Like \log@_message\,
+the contents of \message\ are not expanded until after a condition has failed.
+
+If \message\ is used on a statement that verifies an address, the message
+specified overrides any message that is generated by the verification process.
+However, the original message is available in the variable
+\$acl@_verify@_message$\, so you can incorporate it into your message if you
+wish. In particular, if you want the text from \:fail:\ items in \%redirect%\
+routers to be passed back as part of the SMTP response, you should either not
+use a \message\ modifier, or make use of \$acl@_verify@_message$\.
+
+.item "set <<acl@_name>> = <<value>>"
+This modifier puts a value into one of the ACL variables (see section
+~~SECTaclvariables).
+
+.enditems
+
+
+
+
+.section ACL conditions
+.rset SECTaclconditions "~~chapter.~~section"
+.index ~~ACL||conditions, list of
+Not all conditions are relevant in all circumstances. For example, testing
+senders and recipients does not make sense in an ACL that is being run as the
+result of the arrival of an \\ETRN\\ command, and checks on message headers can
+be done only in the ACLs specified by \acl@_smtp@_data\
+and \acl__not__smtp\.
+You can use the same condition (obviously with different parameters) more than
+once in the same ACL statement. This provides a way of specifying an `and'
+conjunction.
+The conditions are as follows:
+
+.startitems
+
+.item "acl = <<name of acl or ACL string or file name >>"
+.index ~~ACL||nested
+.index ~~ACL||indirect
+The possible values of the argument are the same as for the
+\acl@_smtp@_$it{xxx}\ options. The named or inline ACL is run. If it returns
+`accept' the condition is true; if it returns `deny' the condition is false; if
+it returns `defer', the current ACL returns `defer'.
+If it returns `drop' and the outer condition denies access, the connection is
+dropped. If it returns `discard', the verb must be \accept\ or \discard\, and
+the action is taken immediately -- no further conditions are tested.
+
+ACLs may be nested up to 20 deep; the limit exists purely to catch runaway
+loops. This condition allows you to use different ACLs in different
+circumstances. For example, different ACLs can be used to handle \\RCPT\\
+commands for different local users or different local domains.
+
+.item "authenticated = <<string list>>"
+.index authentication||ACL checking
+.index ~~ACL||testing for authentication
+If the SMTP connection is not authenticated, the condition is false. Otherwise,
+the name of the authenticator is tested against the list. To test for
+authentication by any authenticator, you can set
+.display asis
+authenticated = *
+.endd
+
+.item "condition = <<string>>"
+.index customizing||ACL condition
+.index ~~ACL||customized test
+This feature allows you to make up custom conditions. If the result of
+expanding the string is an empty string, the number zero, or one of the strings
+`no' or `false', the condition is false. If the result is any non-zero number,
+or one of the strings `yes' or `true', the condition is true. For any other
+values, some error is assumed to have occured, and the ACL returns `defer'.
+
+.item "dnslists = <<list of domain names and other data>>"
+.index DNS list||in ACL
+.index black list (DNS)
+.index ~~ACL||testing a DNS list
+This condition checks for entries in DNS black lists. These are also known as
+`RBL lists', after the original Realtime Blackhole List, but note that the use
+of the lists at \*mail-abuse.org*\ now carries a charge.
+There are too many different variants of this condition to describe briefly
+here. See sections ~~SECTmorednslists--~~SECTmorednslistslast for details.
+
+.item "domains = <<domain list>>"
+.index domain||ACL checking
+.index ~~ACL||testing a recipient domain
+This condition is relevant only after a \\RCPT\\ command. It checks that the
+domain of the recipient address is in the domain list. If percent-hack
+processing is enabled, it is done before this test is done. If the check
+succeeds with a lookup, the result of the lookup is placed in \$domain@_data$\
+until the next \domains\ test.
+
+.item "encrypted = <<string list>>"
+.index encryption||checking in an ACL
+.index ~~ACL||testing for encryption
+If the SMTP connection is not encrypted, the condition is false. Otherwise, the
+name of the cipher suite in use is tested against the list. To test for
+encryption without testing for any specific cipher suite(s), set
+.display asis
+encrypted = *
+.endd
+
+.item "hosts = << host list>>"
+.index host||ACL checking
+.index ~~ACL||testing the client host
+This condition tests that the calling host matches the host list. If you have
+name lookups or wildcarded host names and IP addresses in the same host list,
+you should normally put the IP addresses first. For example, you could have:
+.display asis
+accept hosts = 10.9.8.7 : dbm;/etc/friendly/hosts
+.endd
+The reason for this lies in the left-to-right way that Exim processes lists.
+It can test IP addresses without doing any DNS lookups, but when it reaches an
+item that requires a host name, it fails if it cannot find a host name to
+compare with the pattern. If the above list is given in the opposite order, the
+\accept\ statement fails for a host whose name cannot be found, even if its
+IP address is 10.9.8.7.
+
+If you really do want to do the name check first, and still recognize the IP
+address even if the name lookup fails, you can rewrite the ACL like this:
+.display asis
+accept hosts = dbm;/etc/friendly/hosts
+accept hosts = 10.9.8.7
+.endd
+The default action on failing to find the host name is to assume that the host
+is not in the list, so the first \accept\ statement fails. The second statement
+can then check the IP address.
+
+If a \hosts\ condition is satisfied by means of a lookup, the result
+of the lookup is made available in the \$host@_data$\ variable. This
+allows you, for example, to set up a statement like this:
+.display asis
+deny hosts = net-lsearch;/some/file
+ message = $host_data
+.endd
+which gives a custom error message for each denied host.
+
+.item "local@_parts = <<local part list>>"
+.index local part||ACL checking
+.index ~~ACL||testing a local part
+This condition is relevant only after a \\RCPT\\ command. It checks that the
+local part of the recipient address is in the list. If percent-hack processing
+is enabled, it is done before this test. If the check succeeds with a lookup,
+the result of the lookup is placed in \$local@_part@_data$\ until the next
+\local@_parts\ test.
+
+.item "recipients = <<address list>>"
+.index recipient||ACL checking
+.index ~~ACL||testing a recipient
+This condition is relevant only after a \\RCPT\\ command. It checks the entire
+recipient address against a list of recipients.
+
+.item "sender@_domains = <<domain list>>"
+.index sender||ACL checking
+.index ~~ACL||testing a sender domain
+This condition tests the domain of the sender of the message against the given
+domain list.
+\**Note**\: the domain of the sender address is in
+\$sender@_address@_domain$\. It is \*not*\ put in \$domain$\ during the testing
+of this condition. This is an exception to the general rule for testing
+domain lists. It is done this way so that, if this condition is used in an
+ACL for a \\RCPT\\ command, the recipient's domain (which is in \$domain$\) can
+be used to influence the sender checking.
+
+.item "senders = <<address list>>"
+.index sender||ACL checking
+.index ~~ACL||testing a sender
+This condition tests the sender of the message against the given list. To test
+for a bounce message, which has an empty sender, set
+.display asis
+senders = :
+.endd
+
+.item "verify = certificate"
+.index TLS||client certificate verification
+.index certificate||verification of client
+.index ~~ACL||certificate verification
+This condition is true in an SMTP session if the session is encrypted, and a
+certificate was received from the client, and the certificate was verified. The
+server requests a certificate only if the client matches \tls@_verify@_hosts\
+or \tls@_try@_verify@_hosts\ (see chapter ~~CHAPTLS).
+
+.item "verify = header@_sender/<<options>>"
+.index ~~ACL||verifying sender in the header
+.index header lines||verifying the sender in
+.index sender||verifying in header
+.index verifying||sender in header
+This condition is relevant only in an ACL that is run after a message has been
+received, that is, in an ACL specified by \acl@_smtp@_data\. It checks that
+there is a verifiable sender address in at least one of the ::Sender::,
+::Reply-To::, or ::From:: header lines. Details of address verification and the
+options are given later, starting at section ~~SECTaddressverification. You can
+combine this condition with the \senders\ condition to restrict it to bounce
+messages only:
+.display asis
+deny senders = :
+ message = A valid sender header is required for bounces
+ !verify = header_sender
+.endd
+
+.item "verify = header@_syntax"
+.index ~~ACL||verifying header syntax
+.index header lines||verifying syntax
+.index verifying||header syntax
+This condition is relevant only in an ACL that is run after a message has been
+received, that is, in an ACL specified by \acl@_smtp@_data\
+or \acl@_not@_smtp\.
+It checks the syntax of all header lines that can contain lists of addresses
+(::Sender::, ::From::, ::Reply-To::, ::To::, ::Cc::, and ::Bcc::).
+Unqualified addresses (local parts without domains) are permitted only in
+locally generated messages and from hosts that match
+\sender@_unqualified@_hosts\ or \recipient@_unqualified@_hosts\, as
+appropriate.
+
+Note that this condition is a syntax check only. However, a common spamming
+ploy is to send syntactically invalid headers such as
+.display asis
+To: @
+.endd
+and this condition can be used to reject such messages.
+
+.item "verify = helo"
+.index ~~ACL||verifying HELO/EHLO
+.index \\HELO\\||verifying
+.index \\EHLO\\||verifying
+.index verifying||\\EHLO\\
+.index verifying||\\HELO\\
+This condition is true if a \\HELO\\ or \\EHLO\\ command has been received from
+the client host, and its contents have been verified. Verification of these
+commands does not happen by default. See the description of the
+\helo@_verify@_hosts\ and \helo@_try@_verify@_hosts\ options for details of how
+to request it.
+
+.item "verify = recipient/<<options>>"
+.index ~~ACL||verifying recipient
+.index recipient||verifying
+.index verifying||recipient
+This condition is relevant only after a \\RCPT\\ command. It verifies the
+current recipient. Details of address verification are given later, starting at
+section ~~SECTaddressverification. After a recipient has been verified, the
+value of \$address@_data$\ is the last value that was set while routing the
+address. This applies even if the verification fails. When an address that is
+being verified is redirected to a single address, verification continues with
+the new address, and in that case, the subsequent value of \$address@_data$\ is
+the value for the child address.
+
+
+.item "verify = reverse@_host@_lookup"
+.index ~~ACL||verifying host reverse lookup
+.index host||verifying reverse lookup
+This condition ensures that a verified host name has been looked up from the IP
+address of the client host. (This may have happened already if the host name
+was needed for checking a host list, or if the host matched \host@_lookup\.)
+Verification ensures that the host name obtained from a reverse DNS lookup, or
+one of its aliases, does, when it is itself looked up in the DNS, yield the
+original IP address.
+
+If this condition is used for a locally generated message (that is, when there
+is no client host involved), it always succeeds.
+
+
+.item "verify = sender/<<options>>"
+.index ~~ACL||verifying sender
+.index sender||verifying
+.index verifying||sender
+This condition is relevant only after a
+\\MAIL\\ or \\RCPT\\ command, or after a message has been received (the
+\acl@_smtp@_data\ or \acl@_not@_smtp\ ACLs).
+If the message's sender is empty (that is, this is a bounce message), the
+condition is true. Otherwise, the sender address is verified. Details of
+verification are given later, starting at section ~~SECTaddressverification.
+Exim caches the result of sender verification, to avoid doing it more than once
+per message.
+
+.item "verify = sender=address/<<options>>"
+This is a variation of the previous option, in which a modified address is
+verified as a sender.
+
+.enditems
+
+
+
+.section Using DNS lists
+.rset SECTmorednslists "~~chapter.~~section"
+.index DNS list||in ACL
+.index black list (DNS)
+.index ~~ACL||testing a DNS list
+In its simplest form, the \dnslists\ condition tests whether the calling host
+is on a DNS list by looking up the inverted IP address in one or more DNS
+domains. For example, if the calling host's IP address is 192.168.62.43, and
+the ACL statement is
+.display asis
+deny dnslists = blackholes.mail-abuse.org : \
+ dialups.mail-abuse.org
+.endd
+the following domains are looked up:
+.display asis
+43.62.168.192.blackholes.mail-abuse.org
+43.62.168.192.dialups.mail-abuse.org
+.endd
+If a DNS lookup times out or otherwise fails to give a decisive answer, Exim
+behaves as if the host is not on the relevant list. This is usually the
+required action when \dnslists\ is used with \deny\ (which is the most common
+usage), because it prevents a DNS failure from blocking mail. However, you can
+change this behaviour by putting one of the following special items in the
+list:
+.index \"+include@_unknown"\
+.index \"+exclude@_unknown"\
+.index \"+defer@_unknown"\
+.display
++include@_unknown $rm{behave as if the item is on the list}
++exclude@_unknown $rm{behave as if the item is not on the list (default)}
++defer@_unknown $rm{give a temporary error}
+.endd
+Each of these applies to any subsequent items on the list. For example:
+.display asis
+deny dnslists = +defer_unknown : foo.bar.example
+.endd
+
+Testing the list of domains stops as soon as a match is found. If you want to
+warn for one list and block for another, you can use two different statements:
+.display asis
+deny dnslists = blackholes.mail-abuse.org
+warn message = X-Warn: sending host is on dialups list
+ dnslists = dialups.mail-abuse.org
+.endd
+
+DNS list lookups are cached by Exim for the duration of the SMTP session,
+so a lookup based on the IP address is done at most once for any incoming
+connection. Exim does not share information between multiple incoming
+connections (but your local name server cache should be active).
+
+
+.section DNS lists keyed on domain names
+There are some lists that are keyed on domain names rather than inverted IP
+addresses (see for example the \*domain based zones*\ link at
+\?http://www.rfc-ignorant.org/?\).
+.em
+No reversing of components is used with these lists.
+.nem
+You can change the name that is looked up in a DNS list by adding additional
+data to a \dnslists\ item, introduced by a slash. For example,
+.display asis
+deny message = Sender's domain is listed at $dnslist_domain
+ dnslists = dsn.rfc-ignorant.org/$sender_address_domain
+.endd
+This particular example is useful only in ACLs that are obeyed after the
+\\RCPT\\ or \\DATA\\ commands, when a sender address is available. If (for
+example) the message's sender is \*user@@tld.example*\ the name that is looked
+up by this example is
+.display asis
+tld.example.dsn.rfc-ignorant.org
+.endd
+You can mix entries with and without additional data in the same \dnslists\
+condition.
+
+.section Data returned by DNS lists
+DNS lists are constructed using address records in the DNS. The original RBL
+just used the address 127.0.0.1 on the right hand side of each record, but the
+RBL+ list and some other lists use a number of values with different meanings.
+The values used on the RBL+ list are:
+.display rm
+.tabs 12
+127.1.0.1 $t RBL
+127.1.0.2 $t DUL
+127.1.0.3 $t DUL and RBL
+127.1.0.4 $t RSS
+127.1.0.5 $t RSS and RBL
+127.1.0.6 $t RSS and DUL
+127.1.0.7 $t RSS and DUL and RBL
+.endd
+Some DNS lists may return more than one address record.
+
+.section Variables set from DNS lists
+When an entry is found in a DNS list, the variable \$dnslist@_domain$\
+contains the name of the domain that matched, \$dnslist@_value$\ contains the
+data from the entry, and \$dnslist@_text$\ contains the contents of any
+associated TXT record. If more than one address record is returned by the DNS
+lookup, all the IP addresses are included in \$dnslist@_value$\, separated by
+commas and spaces.
+
+You can use these variables in \message\ or \log@_message\ modifiers --
+although these appear before the condition in the ACL, they are not expanded
+until after it has failed. For example:
+.display asis
+deny hosts = !+local_networks
+ message = $sender_host_address is listed \
+ at $dnslist_domain
+ dnslists = rbl-plus.mail-abuse.example
+.endd
+
+
+.section Additional matching conditions for DNS lists
+If you add an equals sign and an IP address after a \dnslists\ domain name, you
+can restrict its action to DNS records with a matching right hand side. For
+example,
+.display asis
+deny dnslists = rblplus.mail-abuse.org=127.0.0.2
+.endd
+rejects only those hosts that yield 127.0.0.2. Without this additional data,
+any address record is considered to be a match. If more than one address record
+is found on the list, they are all checked for a matching right-hand side.
+
+If you want to specify a constraining address and also change the name that is
+looked up, the address list must be specified first. For example:
+.display asis
+deny dnslists = dsn.rfc-ignorant.org\
+ =127.0.0.2/$sender_address_domain
+.endd
+
+More than one IP address may be given for checking, using a comma as a
+separator. These are alternatives -- if any one of them matches, the \dnslists\
+condition is true. For example:
+.display asis
+deny dnslists = a.b.c=127.0.0.2,127.0.0.3
+.endd
+
+If the character `&' is used instead of `=', the comparison for each listed
+IP address is done by a bitwise `and' instead of by an equality test. In
+other words, the listed addresses are used as bit masks. The comparison is
+true if all the bits in the mask are present in the address that is being
+tested. For example:
+.display asis
+dnslists = a.b.c&0.0.0.3
+.endd
+matches if the address is \*x.x.x.*\3, \*x.x.x.*\7, \*x.x.x.*\11, etc. If you
+want to test whether one bit or another bit is present (as opposed to both
+being present), you must use multiple values. For example:
+.display asis
+dnslists = a.b.c&0.0.0.1,0.0.0.2
+.endd
+matches if the final component of the address is an odd number or two times
+an odd number.
+
+
+.section Negated DNS matching conditions
+You can supply a negative list of IP addresses as part of a \dnslists\
+condition. Whereas
+.display asis
+deny dnslists = a.b.c=127.0.0.2,127.0.0.3
+.endd
+means `deny if the host is in the black list at the domain \*a.b.c*\ and the IP
+address yielded by the list is either 127.0.0.2 or 127.0.0.3',
+.display asis
+deny dnslists = a.b.c!=127.0.0.2,127.0.0.3
+.endd
+means `deny if the host is in the black list at the domain \*a.b.c*\ and the IP
+address yielded by the list is not 127.0.0.2 and not 127.0.0.3'. In other
+words, the result of the test is inverted if an exclamation mark appears before
+the `=' (or the `&') sign.
+
+\**Note**\: this kind of negation is not the same as negation in a domain,
+host, or address list (which is why the syntax is different).
+
+If you are using just one list, the negation syntax does not gain you much. The
+previous example is precisely equivalent to
+.display asis
+deny dnslists = a.b.c
+ !dnslists = a.b.c=127.0.0.2,127.0.0.3
+.endd
+However, if you are using multiple lists, the negation syntax is clearer.
+Consider this example:
+.display asis
+deny dnslists = sbl.spamhaus.org : \
+ list.dsbl.org : \
+ dnsbl.njabl.org!=127.0.0.3 : \
+ relays.ordb.org
+.endd
+Using only positive lists, this would have to be:
+.display asis
+deny dnslists = sbl.spamhaus.org : \
+ list.dsbl.org
+deny dnslists = dnsbl.njabl.org
+ !dnslists = dnsbl.njabl.org=127.0.0.3
+deny dnslists = relays.ordb.org
+.endd
+which is less clear, and harder to maintain.
+
+
+
+.section DNS lists and IPv6
+.rset SECTmorednslistslast "~~chapter.~~section"
+If Exim is asked to do a dnslist lookup for an IPv6 address, it inverts it
+nibble by nibble. For example, if the calling host's IP address is
+3ffe:ffff:836f:0a00:000a:0800:200a:c031, Exim might look up
+.display asis
+1.3.0.c.a.0.0.2.0.0.8.0.a.0.0.0.0.0.a.0.f.6.3.8.
+ f.f.f.f.e.f.f.3.blackholes.mail-abuse.org
+.endd
+(split over two lines here to fit on the page). Unfortunately, some of the DNS
+lists contain wildcard records, intended for IPv4, that interact badly with
+IPv6. For example, the DNS entry
+.display asis
+*.3.some.list.example. A 127.0.0.1
+.endd
+is probably intended to put the entire 3.0.0.0/8 IPv4 network on the list.
+Unfortunately, it also matches the entire 3@:@:/124 IPv6 network.
+
+You can exclude IPv6 addresses from DNS lookups by making use of a suitable
+\condition\ condition, as in this example:
+.display asis
+deny condition = ${if isip4{$sender_host_address}{yes}{no}}
+ dnslists = some.list.example
+.endd
+
+
+.section Address verification
+.rset SECTaddressverification "~~chapter.~~section"
+.index verifying||address, options for
+.index policy control||address verification
+Several of the \verify\ conditions described in section ~~SECTaclconditions
+cause addresses to be verified. These conditions can be followed by options
+that modify the verification process. The options are separated from the
+keyword and from each other by slashes, and some of them contain parameters.
+For example:
+.display asis
+verify = sender/callout
+verify = recipient/defer_ok/callout=10s,defer_ok
+.endd
+The first stage of verification is to run the address through the routers, in
+`verify mode'. Routers can detect the difference between verification and
+routing for delivery, and their actions can be varied by a number of generic
+options such as \verify\ and \verify@_only\ (see chapter ~~CHAProutergeneric).
+
+If there is a defer error while doing this verification routing, the ACL
+normally returns `defer'. However, if you include \defer@_ok\ in the options,
+the condition is forced to be true instead.
+
+.section Callout verification
+.rset SECTcallver "~~chapter.~~section"
+.index verifying||address, by callout
+.index callout||verification
+.index SMTP||callout verification
+For non-local addresses, routing verifies the domain, but is unable to do any
+checking of the local part. There are situations where some means of verifying
+the local part is desirable. One way this can be done is to make an SMTP
+\*callback*\ to the sending host (for a sender address) or a \*callforward*\ to
+a subsequent host (for a recipient address), to see if the host accepts the
+address. We use the term \*callout*\ to cover both cases. This facility should
+be used with care, because it can add a lot of resource usage to the cost of
+verifying an address. However, Exim does cache the results of callouts, which
+helps to reduce the cost. Details of caching are in the next section.
+
+.em
+Recipient callouts are usually used only between hosts that are controlled by
+the same administration. For example, a corporate gateway host could use
+callouts to check for valid recipients on an internal mailserver.
+.nem
+A successful callout does not guarantee that a real delivery to the address
+would succeed; on the other hand, a failing callout does guarantee that
+a delivery would fail.
+
+If the \callout\ option is present on a condition that verifies an address, a
+second stage of verification occurs if the address is successfully routed to
+one or more remote hosts. The usual case is routing by a \%dnslookup%\ or a
+\%manualroute%\ router, where the router specifies the hosts. However, if a
+router that does not set up hosts routes to an \%smtp%\ transport with a
+\hosts\ setting, the transport's hosts are used. If an \%smtp%\ transport has
+\hosts@_override\ set, its hosts are always used, whether or not the router
+supplies a host list.
+
+The port that is used is taken from the transport, if it is specified and is a
+remote transport. (For routers that do verification only, no transport need be
+specified.) Otherwise, the default SMTP port is used. If a remote transport
+specifies an outgoing interface, this is used; otherwise the interface is not
+specified.
+
+For a sender callout check, Exim makes SMTP connections to the remote hosts, to
+test whether a bounce message could be delivered to the sender address. The
+following SMTP commands are sent:
+.display
+HELO <<primary host name>>
+MAIL FROM:@<@>
+RCPT TO:<<the address to be tested>>
+QUIT
+.endd
+\\LHLO\\ is used instead of \\HELO\\ if the transport's \protocol\ option is
+set to `lmtp'.
+
+.em
+A recipient callout check is similar. By default, it also uses an empty address
+for the sender. This default is chosen because most hosts do not make use of
+the sender address when verifying a recipient. Using the same address means
+that a single cache entry can be used for each recipient. Some sites, however,
+do make use of the sender address when verifying. These are catered for by the
+\use@_sender\ and \use@_postmaster\ options, described in the next section.
+.nem
+
+If the response to the \\RCPT\\ command is a 2$it{xx} code, the verification
+succeeds. If it is 5$it{xx}, the verification fails. For any other condition,
+Exim tries the next host, if any. If there is a problem with all the remote
+hosts, the ACL yields `defer', unless the \defer@_ok\ parameter of the
+\callout\ option is given, in which case the condition is forced to succeed.
+
+
+.section Additional parameters for callouts
+.rset CALLaddparcall "~~chapter.~~section"
+.index callout||timeout, specifying
+The \callout\ option can be followed by an equals sign and a number of optional
+parameters, separated by commas. For example:
+.display asis
+verify = recipient/callout=10s,defer_ok
+.endd
+The old syntax, which had \callout@_defer@_ok\ and \check@_postmaster\ as
+separate verify options, is retained for backwards compatibility, but is now
+deprecated. The additional parameters for \callout\ are as follows:
+
+.numberpars $.
+<<a time>>: This specifies the timeout that applies for the callout attempt to
+each host. For example:
+.display asis
+verify = sender/callout=5s
+.endd
+The default is 30 seconds. The timeout is used for each response from the
+remote host.
+.nextp
+.index callout||defer, action on
+\defer@_ok\: Failure to contact any host, or any other kind of temporary error
+is treated as success by the ACL. However, the cache is not updated in this
+circumstance.
+.nextp
+.index callout||cache, suppressing
+.index caching||callout, suppressing
+\no@_cache\: The callout cache is neither read nor updated.
+.nextp
+.index callout||postmaster, checking
+\postmaster\: A successful callout check is followed by a similar check for the
+local part \*postmaster*\ at the same domain. If this address is rejected, the
+callout fails. The result of the postmaster check is recorded in a cache
+record; if it is a failure, this is used to fail subsequent callouts for the
+domain without a connection being made, until the cache record expires.
+.nextp
+.index callout||`random' check
+\random\: Before doing the normal callout check, Exim does a
+check for a `random' local part at the same domain. The local part is not
+really random -- it is defined by the expansion of the option
+\callout@_random@_local@_part\, which defaults to
+.display asis
+$primary_host_name-$tod_epoch-testing
+.endd
+The idea here is to try to determine whether the remote host accepts all local
+parts without checking. If it does, there is no point in doing callouts for
+specific local parts. If the `random' check succeeds, the result is saved in
+a cache record, and used to force the current and subsequent callout checks to
+succeed without a connection being made, until the cache record expires.
+.nextp
+.index callout||sender for recipient check
+.em
+\use@_postmaster\: This option applies to recipient callouts only. For example:
+.display asis
+deny !verify = recipient/callout=use_postmaster
+.endd
+It causes a non-empty postmaster address to be used in the \\MAIL\\ command
+when performing the callout. The local part of the address is \"postmaster"\
+and the domain is the contents of \$qualify@_domain$\.
+.nextp
+\use@_sender\: This option applies to recipient callouts only. For example:
+.display asis
+require verify = recipient/callout=use_sender
+.endd
+It causes the message's actual sender address to be used in the \\MAIL\\
+command when performing the callout, instead of an empty address. The cache for
+such callouts is keyed by the sender/recipient combination; thus, for any given
+recipient, many more actual callouts are performed than when an empty sender or
+postmaster is used. This option should be set only when you know that the
+called hosts make use of the sender when checking recipients.
+.nem
+.endp
+
+
+.section Callout caching
+.rset SECTcallvercache "~~chapter.~~section"
+.index hints database||callout cache
+.index callout||caching
+.index caching||callout
+Exim caches the results of callouts in order to reduce the amount of resources
+used, unless you specify the \no@_cache\ parameter with the \callout\ option.
+A hints database called `callout' is used for the cache. Two different record
+types are used: one records the result of a callout check for a specific
+address, and the other records information that applies to the entire domain
+(for example, that it accepts the local part \*postmaster*\).
+
+When an original callout fails, a detailed SMTP error message is given about
+the failure. However, for subsequent failures use the cache data, this message
+is not available.
+
+The expiry times for negative and positive address cache records are
+independent, and can be set by the global options \callout@_negative@_expire\
+(default 2h) and \callout@_positive@_expire\ (default 24h), respectively.
+
+If a host gives a negative response to an SMTP connection, or rejects any
+commands up to and including
+.display asis
+MAIL FROM:<>
+.endd
+.em
+(but not including the \\MAIL\\ command with a non-empty address),
+.nem
+any callout attempt is bound to fail. Exim remembers such failures in a
+domain cache record, which it uses to fail callouts for the domain without
+making new connections, until the domain record times out. There are two
+separate expiry times for domain cache records:
+\callout@_domain@_negative@_expire\ (default 3h) and
+\callout__domain__positive@_expire\ (default 7d).
+
+Domain records expire when the negative expiry time is reached if callouts
+cannot be made for the domain, or if the postmaster check failed.
+Otherwise, they expire when the positive expiry time is reached. This
+ensures that, for example, a host that stops accepting `random' local parts
+will eventually be noticed.
+
+The callout caching mechanism is based entirely on the domain of the
+address that is being tested. If the domain routes to several hosts, it is
+assumed that their behaviour will be the same.
+
+
+.section Sender address verification reporting
+.index verifying||suppressing error details
+When sender verification fails in an ACL, the details of the failure are
+given as additional output lines before the 550 response to the relevant
+SMTP command (\\RCPT\\ or \\DATA\\). For example, if sender callout is in use,
+you might see:
+.display asis
+MAIL FROM:<xyz@abc.example>
+250 OK
+RCPT TO:<pqr@def.example>
+550-Verification failed for <xyz@abc.example>
+550-Called: 192.168.34.43
+550-Sent: RCPT TO:<xyz@abc.example>
+550-Response: 550 Unknown local part xyz in <xyz@abc.example>
+550 Sender verification failed
+.endd
+If more than one \\RCPT\\ command fails in the same way, the details are given
+only for the first of them. However, some administrators do not want to send
+out this much information. You can suppress the details by adding
+`/no@_details' to the ACL statement that requests sender verification. For
+example:
+.display asis
+verify = sender/no_details
+.endd
+
+
+.section Redirection while verifying
+.index verifying||redirection while
+.index address redirection||while verifying
+A dilemma arises when a local address is redirected by aliasing or forwarding
+during verification: should the generated addresses themselves be verified,
+or should the successful expansion of the original address be enough to verify
+it? Exim takes the following pragmatic approach:
+.numberpars $.
+When an incoming address is redirected to just one child address, verification
+continues with the child address, and if that fails to verify, the original
+verification also fails.
+.nextp
+When an incoming address is redirected to more than one child address,
+verification does not continue. A success result is returned.
+.endp
+This seems the most reasonable behaviour for the common use of aliasing as a
+way of redirecting different local parts to the same mailbox. It means, for
+example, that a pair of alias entries of the form
+.display asis
+A.Wol: aw123
+aw123: :fail: Gone away, no forwarding address
+.endd
+work as expected, with both local parts causing verification failure. When a
+redirection generates more than one address, the behaviour is more like a
+mailing list, where the existence of the alias itself is sufficient for
+verification to succeed.
+
+
+.section Using an ACL to control relaying
+.rset SECTrelaycontrol "~~chapter.~~section"
+.index ~~ACL||relay control
+.index relaying||control by ACL
+.index policy control||relay control
+An MTA is said to \*relay*\ a message if it receives it from some host and
+delivers it directly to another host as a result of a remote address contained
+within it. Redirecting a local address via an alias or forward file and then
+passing the message on to another host is not relaying,
+.index `percent hack'
+but a redirection as a result of the `percent hack' is.
+
+Two kinds of relaying exist, which are termed `incoming' and `outgoing'. A host
+which is acting as a gateway or an MX backup is concerned with incoming
+relaying from arbitrary hosts to a specific set of domains. On the other hand,
+a host which is acting as a smart host for a number of clients is concerned
+with outgoing relaying from those clients to the Internet at large. Often the
+same host is fulfilling both functions, as illustrated in the diagram below,
+but in principle these two kinds of relaying are entirely independent. What is
+not wanted is the transmission of mail from arbitrary remote hosts through your
+system to arbitrary domains.
+.if ~~sys.fancy
+.figure "Controlled relaying" rm
+.indent 0
+.call aspic
+centre ~~sys.linelength;
+magnify 0.8;
+boundingbox 30;
+textdepth 16;
+ boxwidth 120;
+ boxdepth 44;
+A: box "Arbitrary" "remote hosts";
+C: ibox;
+D: box "Arbitrary" "domains";
+ iline down 50 from bottom of C;
+H: box width 180 "Local host";
+ iline down 50;
+E: ibox;
+SH: box "Specific" "hosts";
+SD: box join right to E "Specific" "domains";
+ arcarrow clockwise from top of SH to bottom of D plus (-10,-4)
+ via right of H plus (-20,0);
+ arcarrow clockwise from bottom of A to top of SD plus (10,4)
+ via left of H plus (20,0);
+
+ ibox join left to right of H "$it{Outgoing}";
+ goto H;
+ ibox join right to left of H "$it{Incoming}";
+
+L: line dashed from right of A to top of H plus (-15,0);
+ arc dashed to top of H plus (15,0);
+ arrow dashed to left of D plus (-2,0);
+
+ arrow dashed back up 72 right 32 from middle of L plus (8,0);
+ text at end plus (0, 4) "$it{Not wanted}";
+.endcall
+.endfigure
+.elif !~~html
+.display asis
+ -------------- -----------
+ | Arbitrary | |Arbitrary|
+ |remote hosts| | domains |
+ -------------- -----------
+ I v ^ O
+ n v ^ u
+ c ---v----------------^--- t
+ o | v Local ^ | g
+ m | v host ^ | o
+ i ---v----------------^--- i
+ n v ^ n
+ g v ^ g
+ Specific Specific
+ domains hosts
+.endd
+.else
+[(IMG SRC="relaying.gif" alt="Controlled relaying")][(br)]
+.fi
+
+You can implement relay control by means of suitable statements in the ACL that
+runs for each \\RCPT\\ command. For convenience, it is often easiest to use
+Exim's named list facility to define the domains and hosts involved. For
+example, suppose you want to do the following:
+.numberpars $.
+Deliver a number of domains to mailboxes on the local host (or process them
+locally in some other way). Let's say these are \*my.dom1.example*\ and
+\*my.dom2.example*\.
+.nextp
+Relay mail for a number of other domains for which you are the secondary MX.
+These might be \*friend1.example*\ and \*friend2.example*\.
+.nextp
+Relay mail from the hosts on your local LAN, to whatever domains are involved.
+Suppose your LAN is 192.168.45.0/24.
+.endp
+In the main part of the configuration, you put the following definitions:
+.display asis
+domainlist local_domains = my.dom1.example : my.dom2.example
+domainlist relay_domains = friend1.example : friend2.example
+hostlist relay_hosts = 192.168.45.0/24
+.endd
+Now you can use these definitions in the ACL that is run for every \\RCPT\\
+command:
+.display asis
+acl_check_rcpt:
+ accept domains = +local_domains : +relay_domains
+ accept hosts = +relay_hosts
+.endd
+The first statement accepts any \\RCPT\\ command that contains an address in
+the local or relay domains. For any other domain, control passes to the second
+statement, which accepts the command only if it comes from one of the relay
+hosts. In practice, you will probably want to make your ACL more sophisticated
+than this, for example, by including sender and recipient verification. The
+default configuration includes a more comprehensive example, which is described
+in chapter ~~CHAPdefconfil.
+
+
+.section Checking a relay configuration
+.rset SECTcheralcon "~~chapter.~~section"
+.index relaying||checking control of
+You can check the relay characteristics of your configuration in the same way
+that you can test any ACL behaviour for an incoming SMTP connection, by using
+the \-bh-\ option to run a fake SMTP session with which you interact.
+
+For specifically testing for unwanted relaying, the host
+\*relay-test.mail-abuse.org*\ provides a useful service. If you telnet to this
+host from the host on which Exim is running, using the normal telnet port, you
+will see a normal telnet connection message and then quite a long delay. Be
+patient. The remote host is making an SMTP connection back to your host, and
+trying a number of common probes to test for open relay vulnerability. The
+results of the tests will eventually appear on your terminal.
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Adding a local scan function to Exim
+.set runningfoot "local scan function"
+.rset CHAPlocalscan "~~chapter"
+.index \*local@_scan()*\ function||description of
+.index customizing||input scan using C function
+.index policy control||by local scan function
+
+In these days of email worms, viruses, and ever-increasing spam, some sites
+want to apply a lot of checking to messages before accepting them. You can do a
+certain amount through string expansions and the \condition\ condition in the
+ACL that runs after the SMTP \\DATA\\ command or the ACL for non-SMTP messages
+(see chapter ~~CHAPACL), but this has its limitations.
+
+.index \exiscan\
+An increasingly popular way of doing additional checking is to make use of the
+Exiscan patch for Exim, which adds ACL conditions that perform body scans of
+various kinds. This is available from
+.if ~~html
+[(A HREF="http://duncanthrax.net/exiscan-acl/")]
+/?http://duncanthrax.net/exiscan-acl/?\.
+[(/A)]
+.else
+\?http:@/@/duncanthrax.net/exiscan-acl/?\.
+.fi
+
+To allow for even more general checking that can be customized to a site's own
+requirements, there is the possibility of linking Exim with a private message
+scanning function, written in C. If you want to run code that is written in
+something other than C, you can of course use a little C stub to call it.
+
+The local scan function is run once for every incoming message, at the point
+when Exim is just about to accept the message.
+It can therefore be used to control non-SMTP messages from local processes as
+well as messages arriving via SMTP.
+
+Exim applies a timeout to calls of the local scan function, and there is an
+option called \local@_scan@_timeout\ for setting it. The default is 5 minutes.
+Zero means `no timeout'.
+Exim also sets up signal handlers for SIGSEGV, SIGILL, SIGFPE, and SIGBUS
+before calling the local scan function, so that the most common types of crash
+are caught. If the timeout is exceeded or one of those signals is caught, the
+incoming message is rejected with a temporary error if it is an SMTP message.
+For a non-SMTP message, the message is dropped and Exim ends with a non-zero
+code. The incident is logged on the main and reject logs.
+
+
+.section Building Exim to use a local scan function
+.index \*local@_scan()*\ function||building Exim to use
+To make use of the local scan function feature, you must tell Exim where your
+function is before building Exim, by setting \\LOCAL@_SCAN@_SOURCE\\ in your
+\(Local/Makefile)\. A recommended place to put it is in the \(Local)\
+directory, so you might set
+.display asis
+LOCAL_SCAN_SOURCE=Local/local_scan.c
+.endd
+for example. The function must be called \*local@_scan()*\. It is called by
+Exim after it has received a message, when the success return code is about to
+be sent. This is after all the ACLs have been run. The return code from your
+function controls whether the message is actually accepted or not. There is a
+commented template function (that just accepts the message) in the file
+\(src/local@_scan.c)\.
+
+If you want to make use of Exim's run time configuration file to set options
+for your \*local@_scan()*\ function, you must also set
+.display asis
+LOCAL_SCAN_HAS_OPTIONS=yes
+.endd
+in \(Local/Makefile)\ (see section ~~SECTconoptloc below).
+
+
+
+.section API for local@_scan()
+.rset SECTapiforloc "~~chapter.~~section"
+.index \*local@_scan()*\ function||API description
+You must include this line near the start of your code:
+.display asis
+#include "local_scan.h"
+.endd
+This header file defines a number of variables and other values, and the
+prototype for the function itself. Exim is coded to use unsigned char values
+almost exclusively, and one of the things this header defines is a shorthand
+for \"unsigned char"\ called \"uschar"\.
+It also contains the following macro definitions, to simplify casting character
+strings and pointers to character strings:
+.display asis
+#define CS (char *)
+#define CCS (const char *)
+#define CSS (char **)
+#define US (unsigned char *)
+#define CUS (const unsigned char *)
+#define USS (unsigned char **)
+.endd
+
+The function prototype for \*local@_scan()*\ is:
+.display asis
+extern int local_scan(int fd, uschar **return_text);
+.endd
+The arguments are as follows:
+.numberpars $.
+\fd\ is a file descriptor for the file that contains the body of the message
+(the -D file).
+The file is open for reading and writing, but updating it is not recommended.
+\**Warning**\: You must \*not*\ close this file descriptor.
+
+The descriptor is positioned at character 19 of the file, which is the first
+character of the body itself, because the first 19 characters are the message
+id followed by \"-D"\ and a newline. If you rewind the file, you should use the
+macro \\SPOOL@_DATA@_START@_OFFSET\\ to reset to the start of the data, just in
+case this changes in some future version.
+
+.nextp
+\return@_text\ is an address which you can use to return a pointer to a text
+string at the end of the function. The value it points to on entry is NULL.
+.endp
+The function must return an \int\ value which is one of the following macros:
+.numberpars $.
+\"LOCAL@_SCAN@_ACCEPT"\
+
+The message is accepted. If you pass back a string of text, it is saved with
+the message, and made available in the variable \$local@_scan@_data$\. No
+newlines are permitted (if there are any, they are turned into spaces) and the
+maximum length of text is 1000 characters.
+.nextp
+\"LOCAL@_SCAN@_ACCEPT@_FREEZE"\
+
+This behaves as \\LOCAL@_SCAN@_ACCEPT\\, except that the accepted message is
+queued without immediate delivery, and is frozen.
+.nextp
+\"LOCAL@_SCAN@_ACCEPT@_QUEUE"\
+
+This behaves as \\LOCAL@_SCAN@_ACCEPT\\, except that the accepted message is
+queued without immediate delivery.
+.nextp
+\"LOCAL@_SCAN@_REJECT"\
+
+The message is rejected; the returned text is used as an error message which is
+passed back to the sender and which is also logged. Newlines are permitted --
+they cause a multiline response for SMTP rejections, but are converted to
+\"@\n"\ in log lines.
+If no message is given, `Administrative prohibition' is used.
+.nextp
+\"LOCAL@_SCAN@_TEMPREJECT"\
+
+The message is temporarily rejected; the returned text is used as an error
+message as for \\LOCAL@_SCAN@_REJECT\\. If no message is given, `Temporary
+local problem' is used.
+.nextp
+\"LOCAL@_SCAN@_REJECT@_NOLOGHDR"\
+
+This behaves as \\LOCAL@_SCAN@_REJECT\\, except that the header of the rejected
+message is not written to the reject log. It has the effect of unsetting the
+\rejected@_header\ log selector for just this rejection. If \rejected@_header\
+is already unset (see the discussion of the \log@_selection\ option in section
+~~SECTlogselector), this code is the same as \\LOCAL@_SCAN@_REJECT\\.
+
+.nextp
+\"LOCAL@_SCAN@_TEMPREJECT@_NOLOGHDR"\
+
+This code is a variation of \\LOCAL@_SCAN@_TEMPREJECT\\ in the same way that
+\\LOCAL__SCAN__REJECT__NOLOGHDR\\ is a variation of \\LOCAL@_SCAN@_REJECT\\.
+.endp
+
+If the message is not being received by interactive SMTP, rejections are
+reported by writing to \stderr\ or by sending an email, as configured by the
+\-oe-\ command line options.
+
+
+.section Configuration options for local@_scan()
+.rset SECTconoptloc "~~chapter.~~section"
+.index \*local@_scan()*\ function||configuration options
+It is possible to have option settings in the main configuration file
+that set values in static variables in the \*local@_scan()*\ module. If you
+want to do this, you must have the line
+.display asis
+LOCAL_SCAN_HAS_OPTIONS=yes
+.endd
+in your \(Local/Makefile)\ when you build Exim. (This line is in
+\(OS/Makefile-Default)\, commented out). Then, in the \*local@_scan()*\ source
+file, you must define static variables to hold the option values, and a table to
+define them.
+
+The table must be a vector called \local@_scan@_options\, of type
+\"optionlist"\. Each entry is a triplet, consisting of a name, an option type,
+and a pointer to the variable that holds the value. The entries must appear in
+alphabetical order. Following \local@_scan@_options\ you must also define a
+variable called \local@_scan@_options@_count\ that contains the number of
+entries in the table. Here is a short example, showing two kinds of option:
+.display asis
+static int my_integer_option = 42;
+static uschar *my_string_option = US"a default string";
+
+optionlist local_scan_options[] = {
+ { "my_integer", opt_int, &my_integer_option },
+ { "my_string", opt_stringptr, &my_string_option }
+};
+int local_scan_options_count =
+ sizeof(local_scan_options)/sizeof(optionlist);
+.endd
+The values of the variables can now be changed from Exim's runtime
+configuration file by including a local scan section as in this example:
+.display asis
+begin local_scan
+my_integer = 99
+my_string = some string of text...
+.endd
+The available types of option data are as follows:
+
+.startitems
+
+.item opt@_bool
+This specifies a boolean (true/false) option. The address should point to
+a variable of type \"BOOL"\, which will be set to \\TRUE\\ or \\FALSE\\, which
+are macros that are defined as `1' and `0', respectively. If you want to detect
+whether such a variable has been set at all, you can initialize it to
+\\TRUE@_UNSET\\. (BOOL variables are integers underneath, so can hold more than
+two values.)
+
+.item "opt@_fixed"
+This specifies a fixed point number, such as is used for load averages.
+The address should point to a variable of type \"int"\. The value is stored
+multiplied by 1000, so, for example, 1.4142 is truncated and stored as 1414.
+
+.item "opt@_int"
+This specifies an integer; the address should point to a variable of type
+\"int"\. The value may be specified in any of the integer formats accepted by
+Exim.
+
+.item "opt@_mkint"
+This is the same as \opt@_int\, except that when such a value is output in a
+\-bP-\ listing, if it is an exact number of kilobytes or megabytes, it is
+printed with the suffix K or M.
+
+.item "opt@_octint"
+This also specifies an integer, but the value is always interpeted as an
+octal integer, whether or not it starts with the digit zero, and it is
+always output in octal.
+
+.item "opt@_stringptr"
+This specifies a string value; the address must be a pointer to a
+variable that points to a string (for example, of type \"uschar $*$"\).
+
+.item "opt@_time"
+This specifies a time interval value. The address must point to a variable of
+type \"int"\. The value that is placed there is a number of seconds.
+
+.enditems
+
+If the \-bP-\ command line option is followed by \"local@_scan"\, Exim prints
+out the values of all the \*local@_scan()*\ options.
+
+
+.section Available Exim variables
+.index \*local@_scan()*\ function||available Exim variables
+The header \(local@_scan.h)\ gives you access to a number of C variables.
+These are the only ones that are guaranteed to be maintained from release to
+release. Note, however, that you can obtain the value of any Exim variable by
+calling \*expand@_string()*\. The exported variables are as follows:
+
+.startitems
+
+.item "unsigned int debug@_selector"
+This variable is set to zero when no debugging is taking place. Otherwise, it
+is a bitmap of debugging selectors. Two bits are identified for use in
+\*local@_scan()*\; they are defined as macros:
+.numberpars $.
+The \"D@_v"\ bit is set when \-v-\ was present on the command line. This is a
+testing option that is not privileged -- any caller may set it. All the
+other selector bits can be set only by admin users.
+.nextp
+The \"D@_local@_scan"\ bit is provided for use by \*local@_scan()*\; it is set
+by the \"+local@_scan"\ debug selector. It is not included in the default set
+of debugging bits.
+.endp
+Thus, to write to the debugging output only when \"+local@_scan"\ has been
+selected, you should use code like this:
+.display asis
+if ((debug_selector & D_local_scan) != 0)
+ debug_printf("xxx", ...);
+.endd
+
+.item "uschar *expand@_string@_message"
+After a failing call to \*expand@_string()*\ (returned value NULL), the
+variable \expand__string__message\ contains the error message, zero-terminated.
+
+.item "header@_line *header@_list"
+A pointer to a chain of header lines. The \header@_line\ structure is discussed
+below.
+
+.item "header@_line *header@_last"
+A pointer to the last of the header lines.
+
+.item "uschar *headers@_charset"
+The value of the \headers@_charset\ configuration option.
+
+.item "BOOL host@_checking"
+This variable is TRUE during a host checking session that is initiated by the
+\-bh-\ command line option.
+
+.item "uschar *interface@_address"
+The IP address of the interface that received the message, as a string. This
+is NULL for locally submitted messages.
+
+.item "int interface@_port"
+The port on which this message was received.
+
+.item "uschar *message@_id"
+This variable contains the message id for the incoming message as a
+zero-terminated string.
+
+
+.item "uschar *received@_protocol"
+The name of the protocol by which the message was received.
+
+.item "int recipients@_count"
+The number of accepted recipients.
+
+.item "recipient@_item *recipients@_list"
+.index recipient||adding in local scan
+.index recipient||removing in local scan
+The list of accepted recipients, held in a vector of length
+\recipients@_count\. The \recipient@_item\ structure is discussed below. You
+can add additional recipients by calling \*receive@_add@_recipient()*\ (see
+below). You can delete recipients by removing them from the vector and adusting
+the value in \recipients@_count\. In particular, by setting \recipients@_count\
+to zero you remove all recipients. If you then return the value
+\"LOCAL@_SCAN@_ACCEPT"\, the message is accepted, but immediately blackholed.
+To replace the recipients, set \recipients@_count\ to zero and then call
+\*receive@_add@_recipient()*\ as often as needed.
+
+.item "uschar *sender@_address"
+The envelope sender address. For bounce messages this is the empty string.
+
+.item "uschar *sender@_host@_address"
+The IP address of the sending host, as a string. This is NULL for
+locally-submitted messages.
+
+.item "uschar *sender@_host@_authenticated"
+The name of the authentication mechanism that was used, or NULL if the message
+was not received over an authenticated SMTP connection.
+
+.item "uschar *sender@_host@_name"
+The name of the sending host, if known.
+
+.item "int sender@_host@_port"
+The port on the sending host.
+
+.item "BOOL smtp@_input"
+This variable is TRUE for all SMTP input, including BSMTP.
+
+.item "BOOL smtp@_batched@_input"
+This variable is TRUE for BSMTP input.
+
+.item "int store@_pool"
+The contents of this variable control which pool of memory is used for new
+requests. See section ~~SECTmemhanloc for details.
+
+.enditems
+
+
+.section Structure of header lines
+The \header@_line\ structure contains the members listed below.
+You can add additional header lines by calling the \*header@_add()*\ function
+(see below). You can cause header lines to be ignored (deleted) by setting
+their type to $*$.
+
+.startitems
+
+.item "struct header@_line *next"
+A pointer to the next header line, or NULL for the last line.
+
+.item "int type"
+A code identifying certain headers that Exim recognizes. The codes are printing
+characters, and are documented in chapter ~~CHAPspool of this manual. Notice in
+particular that any header line whose type is $*$ is not transmitted with the
+message. This flagging is used for header lines that have been rewritten, or
+are to be removed (for example, ::Envelope-sender:: header lines.) Effectively,
+$*$ means `deleted'.
+
+.item "int slen"
+The number of characters in the header line, including the terminating and any
+internal newlines.
+
+.item "uschar *text"
+A pointer to the text of the header. It always ends with a newline, followed by
+a zero byte. Internal newlines are preserved.
+
+.enditems
+
+
+
+.section Structure of recipient items
+The \recipient@_item\ structure contains these members:
+
+.startitems
+
+.item "uschar *address"
+This is a pointer to the recipient address as it was received.
+
+.item "int pno"
+This is used in later Exim processing when top level addresses are created
+by the \one@_time\ option. It is not relevant at the time \*local@_scan()*\ is
+run and
+must always contain -1 at this stage.
+
+.item "uschar *errors@_to"
+If this value is not NULL, bounce messages caused by failing to deliver to the
+recipient are sent to the address it contains. In other words, it overrides the
+envelope sender for this one recipient. (Compare the \errors@_to\ generic
+router option.)
+If a \*local@_scan()*\ function sets an \errors@_to\ field to an unqualified
+address, Exim qualifies it using the domain from \qualify@_recipient\.
+When \*local@_scan()*\ is called, the \errors@_to\ field is NULL for all
+recipients.
+.enditems
+
+
+.section Available Exim functions
+.index \*local@_scan()*\ function||available Exim functions
+The header \(local@_scan.h)\ gives you access to a number of Exim functions.
+These are the only ones that are guaranteed to be maintained from release to
+release:
+
+.startitems
+
+.item "pid@_t child@_open(uschar **argv, uschar **envp, int newumask, int *infdptr, int *outfdptr, BOOL make@_leader)"
+This function creates a child process that runs the command specified by
+\argv\. The environment for the process is specified by \envp\, which can be
+NULL if no environment variables are to be passed. A new umask is supplied for
+the process in \newumask\.
+
+Pipes to the standard input and output of the new process are set up
+and returned to the caller via the \infdptr\ and \outfdptr\ arguments. The
+standard error is cloned to the standard output. If there are any file
+descriptors `in the way' in the new process, they are closed. If the final
+argument is TRUE, the new process is made into a process group leader.
+
+The function returns the pid of the new process, or -1 if things go wrong.
+
+
+.item "int child@_close(pid@_t pid, int timeout)"
+This function waits for a child process to terminate, or for a timeout (in
+seconds) to expire. A timeout value of zero means wait as long as it takes. The
+return value is as follows:
+.numberpars $.
+>= 0
+
+The process terminated by a normal exit and the value is the process ending
+status.
+.nextp
+< 0 and > --256
+
+The process was terminated by a signal and the value is the negation of the
+signal number.
+.nextp
+--256
+
+The process timed out.
+.nextp
+--257
+
+The was some other error in wait(); \errno\ is still set.
+.endp
+
+
+.item "pid@_t child@_open@_exim(int *fd)"
+This function provide you with a means of submitting a new message to
+Exim. (Of course, you can also call \(/usr/sbin/sendmail)\ yourself if you
+want, but this packages it all up for you.) The function creates a pipe,
+forks a subprocess that is running
+.display asis
+exim -t -oem -oi -f <>
+.endd
+and returns to you (via the \"int *"\ argument) a file descriptor for the pipe
+that is connected to the standard input. The yield of the function is the PID
+of the subprocess. You can then write a message to the file descriptor, with
+recipients in ::To::, ::Cc::, and/or ::Bcc:: header lines.
+
+When you have finished, call \*child@_close()*\ to wait for the process to
+finish and to collect its ending status. A timeout value of zero is usually
+fine in this circumstance. Unless you have made a mistake with the recipient
+addresses, you should get a return code of zero.
+
+.item "void debug@_printf(char *, ...)"
+This is Exim's debugging function, with arguments as for \*(printf()*\. The
+output is written to the standard error stream. If no debugging is selected,
+calls to \*debug@_printf()*\ have no effect. Normally, you should make calls
+conditional on the \"local@_scan"\ debug selector by coding like this:
+.display asis
+if ((debug_selector & D_local_scan) != 0)
+ debug_printf("xxx", ...);
+.endd
+
+.item "uschar *expand@_string(uschar *string)"
+This is an interface to Exim's string expansion code. The return value is the
+expanded string, or NULL if there was an expansion failure.
+The C variable \expand@_string@_message\ contains an error message after an
+expansion failure. If expansion does not change the string, the return value is
+the pointer to the input string. Otherwise, the return value points to a new
+block of memory that was obtained by a call to \*store@_get()*\. See section
+~~SECTmemhanloc below for a discussion of memory handling.
+
+.item "void header@_add(int type, char *format, ...)"
+This function allows you to add additional header lines. The first argument is
+the type, and should normally be a space character. The second argument is a
+format string and any number of substitution arguments as for \*sprintf()*\.
+You may include internal newlines if you want, and you must ensure that the
+string ends with a newline.
+
+.item "uschar *lss@_b64encode(uschar *cleartext, int length)"
+.index base64 encoding||functions for \*local@_scan()*\ use
+This function base64-encodes a string, which is passed by address and length.
+The text may contain bytes of any value, including zero. The result is passed
+back in dynamic memory that is obtained by calling \*store@_get()*\. It is
+zero-terminated.
+
+.item "int lss@_b64decode(uschar *codetext, uschar **cleartext)"
+This function decodes a base64-encoded string. Its arguments are a
+zero-terminated base64-encoded string and the address of a variable that is set
+to point to the result, which is in dynamic memory. The length of the
+decoded string is the yield of the function. If the input is invalid base64
+data, the yield is -1. A zero byte is added to the end of the output string to
+make it easy to interpret as a C string (assuming it contains no zeros of its
+own). The added zero byte is not included in the returned count.
+
+.item "int lss@_match@_domain(uschar *domain, uschar *list)"
+This function checks for a match in a domain list. Domains are always
+matched caselessly. The return value is one of the following:
+.display
+OK $rm{match succeeded}
+FAIL $rm{match failed}
+DEFER $rm{match deferred}
+.endd
+DEFER is usually caused by some kind of lookup defer, such as the
+inability to contact a database.
+
+.item "int lss@_match@_local@_part(uschar *localpart, uschar *list, BOOL caseless)"
+This function checks for a match in a local part list. The third argument
+controls case-sensitivity. The return values are as for
+\*lss@_match@_domain()*\.
+
+.item "int lss@_match@_address(uschar *address, uschar *list, BOOL caseless)"
+This function checks for a match in an address list. The third argument
+controls the case-sensitivity of the local part match. The domain is always
+matched caselessly. The return values are as for \*lss@_match@_domain()*\.
+
+.item "int lss@_match@_host(uschar *host@_name, uschar *host@_address, uschar *list)"
+This function checks for a match in a host list. The most common usage is
+expected to be
+.display asis
+lss_match_host(sender_host_name, sender_host_address, ...)
+.endd
+An empty address field matches an empty item in the host list. If the
+host name is NULL, the name corresponding to \$sender@_host@_address$\ is
+automatically looked up if a host name is required to match an item in the
+list. The return values are as for \*lss@_match@_domain()*\, but in addition,
+\*lss@_match@_host()*\ returns ERROR in the case when it had to look up a host
+name, but the lookup failed.
+
+.item "void log@_write(unsigned int selector, int which, char *format, ...)"
+This function writes to Exim's log files. The first argument should be zero (it
+is concerned with \log@_selector\). The second argument can be \"LOG@_MAIN"\ or
+\"LOG@_REJECT"\ or
+\"LOG@_PANIC"\ or the inclusive `or' of any combination of them. It specifies
+to which log or logs the message is written.
+The remaining arguments are a format and relevant insertion arguments. The
+string should not contain any newlines, not even at the end.
+
+
+.item "void receive@_add@_recipient(uschar *address, int pno)"
+This function adds an additional recipient to the message. The first argument
+is the recipient address. If it is unqualified (has no domain), it is qualified
+with the \qualify@_recipient\ domain. The second argument must always be -1.
+
+This function does not allow you to specify a private \errors@_to\ address (as
+described with the structure of \recipient@_item\ above), because it pre-dates
+the addition of that field to the structure. However, it is easy to add such a
+value afterwards. For example:
+.display asis
+receive_add_recipient(US"monitor@mydom.example", -1);
+recipients_list[recipients_count-1].errors_to =
+ US"postmaster@mydom.example";
+.endd
+
+.item "uschar *rfc2047@_decode(uschar *string, BOOL lencheck, uschar *target, int zeroval, int *lenptr, uschar **error)"
+This function decodes strings that are encoded according to RFC 2047. Typically
+these are the contents of header lines. First, each encoded `word' is decoded
+from the Q or B encoding into a byte-string. Then, if provided with the name of
+a charset encoding, and if the \*iconv()*\ function is available, an attempt is
+made to translate the result to the named character set. If this fails, the
+binary string is returned with an error message.
+
+The first argument is the string to be decoded. If \lencheck\ is TRUE, the
+maximum MIME word length is enforced. The third argument is the target
+encoding, or NULL if no translation is wanted.
+
+.index binary zero||in RFC 2047 decoding
+If a binary zero is encountered in the decoded string, it is replaced by the
+contents of the \zeroval\ argument. For use with Exim headers, the value must
+not be 0 because header lines are handled as zero-terminated strings.
+
+The function returns the result of processing the string, zero-terminated; if
+\lenptr\ is not NULL, the length of the result is set in the variable to which
+it points. When \zeroval\ is 0, \lenptr\ should not be NULL.
+
+If an error is encountered, the function returns NULL and uses the \error\
+argument to return an error message. The variable pointed to by \error\ is set
+to NULL if there is no error; it may be set non-NULL even when the function
+returns a non-NULL value if decoding was successful, but there was a problem
+with translation.
+
+
+.item "int smtp@_fflush(void)"
+This function is used in conjunction with \*smtp@_printf()*\, as described
+below.
+
+.item "void smtp@_printf(char *, ...)"
+The arguments of this function are like \*printf()*\; it writes to the SMTP
+output stream. You should use this function only when there is an SMTP output
+stream, that is, when the incoming message is being received via interactive
+SMTP. This is the case when \smtp@_input\ is TRUE and \smtp@_batched@_input\ is
+FALSE. If you want to test for an incoming message from another host (as
+opposed to a local process that used the \-bs-\ command line option), you can
+test the value of \sender@_host@_address\, which is non-NULL when a remote host
+is involved.
+
+If an SMTP TLS connection is established, \*smtp@_printf()*\ uses the TLS
+output function, so it can be used for all forms of SMTP connection.
+
+Strings that are written by \*smtp@_printf()*\ from within \*local@_scan()*\
+must start with an appropriate response code: 550 if you are going to return
+\\LOCAL@_SCAN@_REJECT\\, 451 if you are going to return
+\\LOCAL@_SCAN@_TEMPREJECT\\, and 250 otherwise. Because you are writing the
+initial lines of a multi-line response, the code must be followed by a hyphen
+to indicate that the line is not the final response line. You must also ensure
+that the lines you write terminate with CRLF. For example:
+.display asis
+smtp_printf("550-this is some extra info\r\n");
+return LOCAL_SCAN_REJECT;
+.endd
+Note that you can also create multi-line responses by including newlines in
+the data returned via the \return@_text\ argument. The added value of using
+\*smtp@_printf()*\ is that, for instance, you could introduce delays between
+multiple output lines.
+
+The \*smtp@_printf()*\ function does not return any error indication, because it
+does not automatically flush pending output, and therefore does not test
+the state of the stream. (In the main code of Exim, flushing and error
+detection is done when Exim is ready for the next SMTP input command.) If
+you want to flush the output and check for an error (for example, the
+dropping of a TCP/IP connection), you can call \*smtp@_fflush()*\, which has no
+arguments. It flushes the output stream, and returns a non-zero value if there
+is an error.
+
+.item "void *store@_get(int)"
+This function accesses Exim's internal store (memory) manager. It gets a new
+chunk of memory whose size is given by the argument. Exim bombs out if it ever
+runs out of memory. See the next section for a discussion of memory handling.
+
+.item "void *store@_get@_perm(int)"
+This function is like \*store@_get()*\, but it always gets memory from the
+permanent pool. See the next section for a discussion of memory handling.
+
+.item "uschar *string@_copy(uschar *string)"
+.item "uschar *string@_copyn(uschar *string, int length)" 0
+.item "uschar *string@_sprintf(char *format, ...)" 0
+These three functions create strings using Exim's dynamic memory facilities.
+The first makes a copy of an entire string. The second copies up to a maximum
+number of characters, indicated by the second argument. The third uses a format
+and insertion arguments to create a new string. In each case, the result is a
+pointer to a new string
+in the current memory pool. See the next section for more discussion.
+
+.enditems
+
+
+
+.section More about Exim's memory handling
+.rset SECTmemhanloc "~~chapter.~~section"
+.index \*local@_scan()*\ function||memory handling
+No function is provided for freeing memory, because that is never needed.
+The dynamic memory that Exim uses when receiving a message is automatically
+recycled if another message is received by the same process (this applies only
+to incoming SMTP connections -- other input methods can supply only one message
+at a time). After receiving the last message, a reception process terminates.
+
+Because it is recycled, the normal dynamic memory cannot be used for holding
+data that must be preserved over a number of incoming messages on the same SMTP
+connection. However, Exim in fact uses two pools of dynamic memory; the second
+one is not recycled, and can be used for this purpose.
+
+If you want to allocate memory that remains available for subsequent messages
+in the same SMTP connection, you should set
+.display asis
+store_pool = POOL_PERM
+.endd
+before calling the function that does the allocation. There is no need to
+restore the value if you do not need to; however, if you do want to revert to
+the normal pool, you can either restore the previous value of \store@_pool\ or
+set it explicitly to \\POOL@_MAIN\\.
+
+The pool setting applies to all functions that get dynamic memory, including
+\*expand@_string()*\, \*store@_get()*\, and the \*string@_xxx()*\ functions.
+There is also a convenience function called \*store@_get@_perm()*\ that gets a
+block of memory from the permanent pool while preserving the value of
+\store@_pool\.
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter System-wide message filtering
+.set runningfoot "system filtering"
+.rset CHAPsystemfilter "~~chapter"
+.index filter||system filter
+.index filtering all mail
+.index system filter
+The previous chapters (on ACLs and the local scan function) describe checks
+that can be applied to messages before they are accepted by a host. There is
+also a mechanism for checking messages once they have been received, but before
+they are delivered. This is called the $it{system filter}.
+
+The system filter operates in a similar manner to users' filter files, but it
+is run just once per message (however many recipients the message has).
+It should not normally be used as a substitute for routing, because \deliver\
+commands in a system router provide new envelope recipient addresses.
+The system filter must be an Exim filter. It cannot be a Sieve filter.
+
+The system filter is run at the start of a delivery attempt, before any routing
+is done. If a message fails to be completely delivered at the first attempt,
+the system filter is run again at the start of every retry.
+If you want your filter to do something only once per message, you can make use
+of the \first@_delivery\ condition in an \if\ command in the filter to prevent
+it happening on retries.
+
+\**Warning**\: Because the system filter runs just once, variables that are
+specific to individual recipient addresses, such as \$local@_part$\ and
+\$domain$\, are not set, and the `personal' condition is not meaningful. If you
+want to run a centrally-specified filter for each recipient address
+independently, you can do so by setting up a suitable \%redirect%\ router, as
+described in section ~~SECTperaddfil below.
+
+.section Specifying a system filter
+.index uid (user id)||system filter
+.index gid (group id)||system filter
+The name of the file that contains the system filter must be specified by
+setting \system@_filter\. If you want the filter to run under a uid and gid
+other than root, you must also set \system@_filter@_user\ and
+\system@_filter@_group\ as appropriate. For example:
+.display asis
+system_filter = /etc/mail/exim.filter
+system_filter_user = exim
+.endd
+If a system filter generates any deliveries directly to files or pipes (via the
+\save\ or \pipe\ commands), transports to handle these deliveries must be
+specified by setting \system@_filter@_file@_transport\ and
+\system@_filter@_pipe@_transport\, respectively. Similarly,
+\system@_filter@_reply@_transport\ must be set to handle any messages generated
+by the \reply\ command.
+
+.section Testing a system filter
+You can run simple tests of a system filter in the same way as for a user
+filter, but you should use \-bF-\ rather than \-bf-\, so that features that
+are permitted only in system filters are recognized.
+
+.section Contents of a system filter
+The language used to specify system filters is the same as for users' filter
+files. It is described in the separate end-user document \*Exim's interface to
+mail filtering*\. However, there are some additional features that are
+available only in system filters; these are described in subsequent sections.
+If they are encountered in a user's filter file or when testing with \-bf-\,
+they cause errors.
+
+.index frozen messages||manual thaw, testing in filter
+There are two special conditions which, though available in users' filter
+files, are designed for use in system filters. The condition \first@_delivery\
+is true only for the first attempt at delivering a message, and
+\manually@_thawed\ is true only if the message has been frozen, and
+subsequently thawed by an admin user. An explicit forced delivery counts as a
+manual thaw, but thawing as a result of the \auto__thaw\ setting does not.
+
+\**Warning**\: If a system filter uses the \first@_delivery\ condition to
+specify an `unseen' (non-significant) delivery, and that delivery does not
+succeed, it will not be tried again.
+If you want Exim to retry an unseen delivery until it succeeds, you should
+arrange to set it up every time the filter runs.
+
+When a system filter finishes running, the values of the variables \$n0$\ --
+\$n9$\ are copied into \$sn0$\ -- \$sn9$\ and are thereby made available to
+users' filter files. Thus a system filter can, for example, set up `scores' to
+which users' filter files can refer.
+
+
+.section Additional variable for system filters
+The expansion variable \$recipients$\, containing a list of all the recipients
+of the message (separated by commas and white space), is available in system
+filters. It is not available in users' filters for privacy reasons.
+
+
+.section Defer, freeze, and fail commands for system filters
+.index freezing messages
+.index message||freezing
+.index message||forced failure
+.index \fail\||in system filter
+.index \freeze\ in system filter
+.index \defer\ in system filter
+There are three extra commands (\defer\, \freeze\ and \fail\) which are always
+available in system filters, but are not normally enabled in users' filters.
+(See the \allow@_defer\,
+\allow@_freeze\ and \allow@_fail\ options for the \%redirect%\ router.) These
+commands can optionally be followed by the word \text\ and a string containing
+an error message, for example:
+.display asis
+fail text "this message looks like spam to me"
+.endd
+The keyword \text\ is optional if the next character is a double quote.
+
+The \defer\ command defers delivery of the original recipients of the message.
+The \fail\ command causes all the original recipients to be failed, and a
+bounce message to be created. The \freeze\ command suspends all delivery
+attempts for the original recipients. In all cases, any new deliveries that are
+specified by the filter are attempted as normal after the filter has run.
+
+The \freeze\ command is ignored if the message has been manually unfrozen and
+not manually frozen since. This means that automatic freezing by a system
+filter can be used as a way of checking out suspicious messages. If a message
+is found to be all right, manually unfreezing it allows it to be delivered.
+
+.index log||\fail\ command log line
+.index \fail\||log line, reducing
+The text given with a fail command is used as part of the bounce message as
+well as being written to the log. If the message is quite long, this can fill
+up a lot of log space when such failures are common. To reduce the size of the
+log message, Exim interprets the text in a special way if it starts with the
+two characters \"@<@<"\ and contains \"@>@>"\ later. The text between these two
+strings is written to the log, and the rest of the text is used in the bounce
+message. For example:
+.display asis
+fail "<<filter test 1>>Your message is rejected \
+ because it contains attachments that we are \
+ not prepared to receive."
+.endd
+
+.index loop||caused by \fail\
+Take great care with the \fail\ command when basing the decision to fail on the
+contents of the message, because the bounce message will of course include the
+contents of the original message and will therefore trigger the \fail\ command
+again (causing a mail loop) unless steps are taken to prevent this. Testing the
+\error@_message\ condition is one way to prevent this. You could use, for
+example
+.display asis
+if $message_body contains "this is spam" and not error_message
+ then fail text "spam is not wanted here" endif
+.endd
+though of course that might let through unwanted bounce messages. The
+alternative is clever checking of the body and/or headers to detect bounces
+generated by the filter.
+
+The interpretation of a system filter file ceases after a
+\defer\,
+\freeze\, or \fail\ command is obeyed. However, any deliveries that were set up
+earlier in the filter file are honoured, so you can use a sequence such as
+.display asis
+mail ...
+freeze
+.endd
+to send a specified message when the system filter is freezing (or deferring or
+failing) a message. The normal deliveries for the message do not, of course,
+take place.
+
+
+.section Adding and removing headers in a system filter
+.index header lines||adding in system filter
+.index header lines||removing in system filter
+.index filter||header lines, adding/removing
+Two filter commands that are available only in system filters are:
+.display asis
+headers add <<string>>
+headers remove <<string>>
+.endd
+The argument for the \headers add\ is a string which is expanded and then added
+to the end of the message's headers. It is the responsibility of the filter
+maintainer to make sure it conforms to RFC 2822 syntax. Leading white space is
+ignored, and if the string is otherwise empty, or if the expansion is forced to
+fail, the command has no effect.
+
+If the message is not delivered at the first attempt, header lines that were
+added by the system filter are stored with the message, and so are still
+present at the next delivery attempt. For that reason, it is usual to make the
+\headers add\ command conditional on \first@_delivery\.
+
+.em
+You can use `@\n' within the string, followed by white space, to specify
+continued header lines. More than one header may be added in one command by
+including `@\n' within the string without any following white space. For
+example:
+.display asis
+headers add "X-header-1: ....\n \
+ continuation of X-header-1 ...\n\
+ X-header-2: ...."
+.endd
+Note that the header line continuation white space after the first newline must
+be placed before the backslash that continues the input string, because white
+space after input continuations is ignored.
+
+Header lines that are added by a system filter are visible to users' filter
+files and to all routers and transports.
+.nem
+
+The argument for \headers remove\ is a colon-separated list of header names.
+This command applies only to those headers that are stored with the message;
+those that are added at delivery time (such as ::Envelope-To:: and
+::Return-Path::) cannot be removed by this means.
+If there is more than one header with the same name, they are all removed.
+
+
+.section Setting an errors address in a system filter
+.index envelope sender
+In a system filter, if a \deliver\ command is followed by
+.display
+errors@_to <<some address>>
+.endd
+in order to change the envelope sender (and hence the error reporting) for that
+delivery, any address may be specified. (In a user filter, only the current
+user's address can be set.) For example, if some mail is being monitored, you
+might use
+.display asis
+unseen deliver monitor@spying.example errors_to root@local.example
+.endd
+to take a copy which would not be sent back to the normal error reporting
+address if its delivery failed.
+
+
+.section Per-address filtering
+.rset SECTperaddfil "~~chapter.~~section"
+In contrast to the system filter, which is run just once per message for each
+delivery attempt, it is also possible to set up a system-wide filtering
+operation that runs once for each recipient address. In this case, variables
+such as \$local@_part$\ and \$domain$\ can be used, and indeed, the choice of
+filter file could be made dependent on them. This is an example of a router
+which implements such a filter:
+.display asis
+central_filter:
+.newline
+.em
+ check_local_user
+.newline
+.nem
+ driver = redirect
+ domains = +local_domains
+ file = /central/filters/$local_part
+ no_verify
+ allow_filter
+ allow_freeze
+.endd
+.em
+The filter is run in a separate process under its own uid. Therefore, either
+\check@_local@_user\ must be set (as above), in which case the filter is run as
+the local user, or the \user\ option must be used to specify which user to use.
+If both are set, \user\ overrides.
+.nem
+
+Care should be taken to ensure that none of the commands in the filter file
+specify a significant delivery if the message is to go on to be delivered to
+its intended recipient. The router will not then claim to have dealt with the
+address, so it will be passed on to subsequent routers to be delivered in the
+normal way.
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Customizing bounce and warning messages
+.set runningfoot "customizing messages"
+.rset CHAPemsgcust "~~chapter"
+When a message fails to be delivered, or remains on the queue for more than a
+configured amount of time, Exim sends a message to the original sender, or
+to an alternative configured address. The text of these messages is built into
+the code of Exim, but it is possible to change it, either by adding a single
+string, or by replacing each of the paragraphs by text supplied in a file.
+
+The ::From:: and ::To:: header lines are automatically generated; you can cause
+a ::Reply-To:: line to be added by setting the \errors@_reply@_to\ option. Exim
+also adds the line
+.display asis
+Auto-Submitted: auto-generated
+.endd
+to all warning and bounce messages,
+
+.section Customizing bounce messages
+.index customizing||bounce message
+.index bounce message||customizing
+If \bounce@_message@_text\ is set, its contents are included in the default
+message immediately after `This message was created automatically by mail
+delivery software.' The string is not expanded. It is not used if
+\bounce@_message@_file\ is set.
+
+When \bounce@_message@_file\ is set, it must point to a template file for
+constructing error messages. The file consists of a series of text items,
+separated by lines consisting of exactly four asterisks. If the file cannot be
+opened, default text is used and a message is written to the main and panic
+logs. If any text item in the file is empty, default text is used for that
+item.
+
+Each item of text that is read from the file is expanded, and there are two
+expansion variables which can be of use here: \$bounce@_recipient$\ is set to
+the recipient of an error message while it is being created, and
+\$return@_size@_limit$\ contains the value of the \return@_size@_limit\ option,
+rounded to a whole number.
+
+The items must appear in the file in the following order:
+.numberpars $.
+The first item is included in the headers, and should include at least a
+::Subject:: header. Exim does not check the syntax of these headers.
+.nextp
+The second item forms the start of the error message. After it, Exim lists the
+failing addresses with their error messages.
+.nextp
+The third item is used to introduce any text from pipe transports that is to be
+returned to the sender. It is omitted if there is no such text.
+.nextp
+The fourth item is used to introduce the copy of the message that is returned
+as part of the error report.
+.nextp
+The fifth item is added after the fourth one if the returned message is
+truncated because it is bigger than \return@_size@_limit\.
+.nextp
+The sixth item is added after the copy of the original message.
+.endp
+The default state (\bounce@_message@_file\ unset) is equivalent to the
+following file, in which the sixth item is empty. The ::Subject:: line has been
+split into two here in order to fit it on the page:
+.if ~~sys.fancy
+.display flow asis
+.fontgroup 0
+.font 54
+.else
+.rule
+.display flow asis
+.linelength 80em
+.indent 0
+.fi
+Subject: Mail delivery failed
+ ${if eq{$sender_address}{$bounce_recipient}{: returning message to sender}}
+****
+This message was created automatically by mail delivery software.
+
+A message ${if eq{$sender_address}{$bounce_recipient}{that you sent }{sent by
+
+ <$sender_address>
+
+}}could not be delivered to all of its recipients.
+The following address(es) failed:
+****
+The following text was generated during the delivery attempt(s):
+****
+------ This is a copy of the message, including all the headers. ------
+****
+------ The body of the message is $message_size characters long; only the first
+------ $return_size_limit or so are included here.
+****
+.endd
+.if !~~sys.fancy
+.rule
+.fi
+
+.section Customizing warning messages
+.rset SECTcustwarn "~~chapter.~~section"
+.index customizing||warning message
+.index warning of delay||customizing the message
+The option
+\warn@_message@_file\
+can be pointed at a template file for use when
+warnings about message delays are created. In this case there are only three
+text sections:
+.numberpars $.
+The first item is included in the headers, and should include at least a
+::Subject:: header. Exim does not check the syntax of these headers.
+.nextp
+The second item forms the start of the warning message. After it, Exim lists
+the delayed addresses.
+.nextp
+The third item then ends the message.
+.endp
+The default state is equivalent to the following file, except that the line
+starting `A message' has been split here, in order to fit it on the page:
+.if ~~sys.fancy
+.display asis
+.fontgroup 0
+.font 54
+.else
+.rule
+.display asis
+.linelength 80em
+.indent 0
+.fi
+.newline
+Subject: Warning: message $message_id delayed $warn_message_delay
+****
+This message was created automatically by mail delivery software.
+
+A message ${if eq{$sender_address}{$warn_message_recipients}
+ {that you sent }{sent by
+
+ <$sender_address>
+
+}}has not been delivered to all of its recipients after
+more than $warn_message_delay on the queue on $primary_hostname.
+.newline
+
+The message identifier is: $message_id
+The subject of the message is: $h_subject
+The date of the message is: $h_date
+
+The following address(es) have not yet been delivered:
+****
+No action is required on your part. Delivery attempts will continue for
+some time, and this warning may be repeated at intervals if the message
+remains undelivered. Eventually the mail delivery software will give up,
+and when that happens, the message will be returned to you.
+.endd
+.if !~~sys.fancy
+.rule
+.fi
+except that in the default state the subject and date lines are omitted if no
+appropriate headers exist. During the expansion of this file,
+\$warn@_message@_delay$\
+is set to the delay time in one of the forms `<<n>> minutes'
+or `<<n>> hours', and
+\$warn@_message@_recipients$\
+contains a list of recipients for the warning message. There may be more than
+one if there are multiple addresses with different \errors@_to\ settings on the
+routers that handled them.
+
+
+
+
+.
+.
+.
+. ============================================================================
+.chapter Some common configuration requirements
+.set runningfoot "common configuration requirements"
+.rset CHAPcomconreq "~~chapter"
+This chapter discusses some configuration requirements that seem to be fairly
+common. More examples and discussion can be found in the Exim book.
+
+
+.section Sending mail to a smart host
+.index smart host||example router
+If you want to send all mail for non-local domains to a `smart host', you
+should replace the default \%dnslookup%\ router with a router which does the
+routing explicitly:
+.display asis
+send_to_smart_host:
+ driver = manualroute
+ route_list = !+local_domains smart.host.name
+ transport = remote_smtp
+.endd
+You can use the smart host's IP address instead of the name if you wish.
+
+
+.section Using Exim to handle mailing lists
+.rset SECTmailinglists "~~chapter.~~section"
+.index mailing lists
+Exim can be used to run simple mailing lists, but for large and/or complicated
+requirements, the use of additional specialized mailing list software such as
+Majordomo or Mailman is recommended.
+
+The \%redirect%\ router can be used to handle mailing lists where each list
+is maintained in a separate file, which can therefore be managed by an
+independent manager. The \domains\ router option can be used to run these
+lists in a separate domain from normal mail. For example:
+.display asis
+lists:
+ driver = redirect
+ domains = lists.example
+ file = /usr/lists/$local_part
+ forbid_pipe
+ forbid_file
+ errors_to = $local_part-request@lists.example
+ no_more
+.endd
+This router is skipped for domains other than \*lists.example*\. For addresses
+in that domain, it looks for a file that matches the local part. If there is no
+such file, the router declines, but because \no@_more\ is set, no subsequent
+routers are tried, and so the whole delivery fails.
+
+The \forbid@_pipe\ and \forbid@_file\ options prevent a local part from being
+expanded into a file name or a pipe delivery, which is usually inappropriate in
+a mailing list.
+
+.index \errors@_to\
+The \errors@_to\ option specifies that any delivery errors caused by addresses
+taken from a mailing list are to be sent to the given address rather than the
+original sender of the message. However, before acting on this, Exim verifies
+the error address, and ignores it if verification fails.
+
+For example, using the configuration above, mail sent to
+\*dicts@@lists.example*\ is passed on to those addresses contained in
+\(/usr/lists/dicts)\, with error reports directed to
+\*dicts-request@@lists.example*\, provided that this address can be verified.
+There could be a file called \(/usr/lists/dicts-request)\ containing
+the address(es) of this particular list's manager(s), but other approaches,
+such as setting up an earlier router (possibly using the \local@_part@_prefix\
+or \local@_part@_suffix\ options) to handle addresses of the form \owner-xxx\
+or \xxx-request\, are also possible.
+
+
+.section Syntax errors in mailing lists
+.index mailing lists||syntax errors in
+If an entry in redirection data contains a syntax error, Exim normally defers
+delivery of the original address. That means that a syntax error in a mailing
+list holds up all deliveries to the list. This may not be appropriate when a
+list is being maintained automatically from data supplied by users, and the
+addresses are not rigorously checked.
+
+If the \skip@_syntax@_errors\ option is set, the \%redirect%\ router just skips
+entries that fail to parse, noting the incident in the log. If in addition
+\syntax@_errors@_to\ is set to a verifiable address, a message is sent to it
+whenever a broken address is skipped. It is usually appropriate to set
+\syntax@_errors@_to\ to the same address as \errors@_to\.
+
+
+.section Re-expansion of mailing lists
+.index mailing lists||re-expansion of
+Exim remembers every individual address to which a message has been delivered,
+in order to avoid duplication, but it normally stores only the original
+recipient addresses with a message. If all the deliveries to a mailing list
+cannot be done at the first attempt, the mailing list is re-expanded when the
+delivery is next tried. This means that alterations to the list are taken into
+account at each delivery attempt, so addresses that have been added to
+the list since the message arrived will therefore receive a copy of the
+message, even though it pre-dates their subscription.
+
+If this behaviour is felt to be undesirable, the \one@_time\ option can be set
+on the \%redirect%\ router. If this is done, any addresses generated by the
+router that fail to deliver at the first attempt are added to the message as
+`top level' addresses, and the parent address that generated them is marked
+`delivered'. Thus, expansion of the mailing list does not happen again at the
+subsequent delivery attempts. The disadvantage of this is that if any of the
+failing addresses are incorrect, correcting them in the file has no effect on
+pre-existing messages.
+
+The original top-level address is remembered with each of the generated
+addresses, and is output in any log messages. However, any intermediate parent
+addresses are not recorded. This makes a difference to the log only if the
+\all@_parents\ selector is set, but for mailing lists there is normally only
+one level of expansion anyway.
+
+
+.section Closed mailing lists
+.index mailing lists||closed
+The examples so far have assumed open mailing lists, to which anybody may
+send mail. It is also possible to set up closed lists, where mail is accepted
+from specified senders only. This is done by making use of the generic
+\senders\ option to restrict the router that handles the list.
+
+The following example uses the same file as a list of recipients and as a list
+of permitted senders. It requires three routers:
+.display asis
+lists_request:
+ driver = redirect
+ domains = lists.example
+ local_part_suffix = -request
+ file = /usr/lists/$local_part$local_part_suffix
+ no_more
+
+lists_post:
+ driver = redirect
+ domains = lists.example
+ senders = ${if exists {/usr/lists/$local_part}\
+ {lsearch;/usr/lists/$local_part}{*}}
+ file = /usr/lists/$local_part
+ forbid_pipe
+ forbid_file
+ errors_to = $local_part-request@lists.example
+ no_more
+
+lists_closed:
+ driver = redirect
+ domains = lists.example
+ allow_fail
+ data = :fail: $local_part@lists.example is a closed mailing list
+.endd
+All three routers have the same \domains\ setting, so for any other domains,
+they are all skipped. The first router runs only if the local part ends in
+\@-request\. It handles messages to the list manager(s) by means of an open
+mailing list.
+
+The second router runs only if the \senders\ precondition is satisfied. It
+checks for the existence of a list that corresponds to the local part, and then
+checks that the sender is on the list by means of a linear search. It is
+necessary to check for the existence of the file before trying to search it,
+because otherwise Exim thinks there is a configuration error. If the file does
+not exist, the expansion of \senders\ is $*$, which matches all senders. This
+means that the router runs, but because there is no list, declines, and
+\no@_more\ ensures that no further routers are run. The address fails with an
+`unrouteable address' error.
+
+The third router runs only if the second router is skipped, which happens when
+a mailing list exists, but the sender is not on it. This router forcibly fails
+the address, giving a suitable error message.
+
+
+
+.section Virtual domains
+.rset SECTvirtualdomains "~~chapter.~~section"
+.index virtual domains
+.index domain||virtual
+The phrase \*virtual domain*\ is unfortunately used with two rather different
+meanings:
+.numberpars $.
+A domain for which there are no real mailboxes; all valid local parts are
+aliases for other email addresses. Common examples are organizational
+top-level domains and `vanity' domains.
+.nextp
+One of a number of independent domains that are all handled by the same host,
+with mailboxes on that host, but where the mailbox owners do not necessarily
+have login accounts on that host.
+.endp
+The first usage is probably more common, and does seem more `virtual' than the
+second. This kind of domain can be handled in Exim with a straightforward
+aliasing router. One approach is to create a separate alias file for each
+virtual domain. Exim can test for the existence of the alias file to determine
+whether the domain exists. The \%dsearch%\ lookup type is useful here, leading
+to a router of this form:
+.display asis
+virtual:
+ driver = redirect
+ domains = dsearch;/etc/mail/virtual
+ data = ${lookup{$local_part}lsearch{/etc/mail/virtual/$domain}}
+ no_more
+.endd
+The \domains\ option specifies that the router is to be skipped, unless there
+is a file in the \(/etc/mail/virtual)\ directory whose name is the same as the
+domain that is being processed. When the router runs, it looks up the local
+part in the file to find a new address (or list of addresses). The \no@_more\
+setting ensures that if the lookup fails (leading to \data\ being an empty
+string), Exim gives up on the address without trying any subsequent routers.
+
+This one router can handle all the virtual domains because the alias file names
+follow a fixed pattern. Permissions can be arranged so that appropriate people
+can edit the different alias files. A successful aliasing operation results in
+a new envelope recipient address, which is then routed from scratch.
+
+The other kind of `virtual' domain can also be handled in a straightforward
+way. One approach is to create a file for each domain containing a list of
+valid local parts, and use it in a router like this:
+.display asis
+my_domains:
+ driver = accept
+ domains = dsearch;/etc/mail/domains
+ local_parts = lsearch;/etc/mail/domains/$domain
+ transport = my_mailboxes
+.endd
+The address is accepted if there is a file for the domain, and the local part
+can be found in the file. The \domains\ option is used to check for the file's
+existence because \domains\ is tested before the \local@_parts\ option (see
+section ~~SECTrouprecon). You can't use \require@_files\, because that option
+is tested after \local@_parts\. The transport is as follows:
+.display asis
+my_mailboxes:
+ driver = appendfile
+ file = /var/mail/$domain/$local_part
+ user = mail
+.endd
+This uses a directory of mailboxes for each domain. The \user\ setting is
+required, to specify which uid is to be used for writing to the mailboxes.
+
+The configuration shown here is just one example of how you might support this
+requirement. There are many other ways this kind of configuration can be set
+up, for example, by using a database instead of separate files to hold all the
+information about the domains.
+
+
+.section Multiple user mailboxes
+.rset SECTmulbox "~~chapter.~~section"
+.index multiple mailboxes
+.index mailbox||multiple
+.index local part||prefix
+.index local part||suffix
+Heavy email users often want to operate with multiple mailboxes, into which
+incoming mail is automatically sorted. A popular way of handling this is to
+allow users to use multiple sender addresses, so that replies can easily be
+identified. Users are permitted to add prefixes or suffixes to their local
+parts for this purpose. The wildcard facility of the generic router options
+\local@_part@_prefix\ and \local@_part@_suffix\ can be used for this. For
+example, consider this router:
+.display asis
+userforward:
+ driver = redirect
+ check_local_user
+ file = $home/.forward
+ local_part_suffix = -*
+ local_part_suffix_optional
+ allow_filter
+.endd
+It runs a user's \(.forward)\ file for all local parts of the form
+\*username-$*$*\. Within the filter file the user can distinguish different
+cases by testing the variable \$local@_part@_suffix$\. For example:
+.display asis
+if $local_part_suffix contains -special then
+ save /home/$local_part/Mail/special
+endif
+.endd
+If the filter file does not exist, or does not deal with such addresses, they
+fall through to subsequent routers, and, assuming no subsequent use of the
+\local@_part@_suffix\ option is made, they presumably fail. Thus, users have
+control over which suffixes are valid.
+
+Alternatively, a suffix can be used to trigger the use of a different
+\(.forward)\ file -- which is the way a similar facility is implemented in
+another MTA:
+.display asis
+userforward:
+ driver = redirect
+ check_local_user
+ file = $home/.forward$local_part_suffix
+ local_part_suffix = -*
+ local_part_suffix_optional
+ allow_filter
+.endd
+If there is no suffix, \(.forward)\ is used; if the suffix is \*-special*\, for
+example, \(.forward-special)\ is used. Once again, if the appropriate file
+does not exist, or does not deal with the address, it is passed on to
+subsequent routers, which could, if required, look for an unqualified
+\(.forward)\ file to use as a default.
+
+
+.section Simplified vacation processing
+.index vacation processing
+The traditional way of running the \*vacation*\ program is for a user to set up
+a pipe command in a \(.forward)\ file
+(see section ~~SECTspecitredli for syntax details).
+This is prone to error by inexperienced users. There are two features of Exim
+that can be used to make this process simpler for users:
+.numberpars $.
+A local part prefix such as `vacation-' can be specified on a router which
+can cause the message to be delivered directly to the \*vacation*\ program, or
+alternatively can use Exim's \%autoreply%\ transport. The contents of a user's
+\(.forward)\ file are then much simpler. For example:
+.display asis
+spqr, vacation-spqr
+.endd
+.nextp
+The \require@_files\ generic router option can be used to trigger a
+vacation delivery by checking for the existence of a certain file in the
+user's home directory. The \unseen\ generic option should also be used, to
+ensure that the original delivery also proceeds. In this case, all the user has
+to do is to create a file called, say, \(.vacation)\, containing a vacation
+message.
+.endp
+Another advantage of both these methods is that they both work even when the
+use of arbitrary pipes by users is locked out.
+
+
+.section Taking copies of mail
+.index message||copying every
+Some installations have policies that require archive copies of all messages to
+be made. A single copy of each message can easily be taken by an appropriate
+command in a system filter, which could, for example, use a different file for
+each day's messages.
+
+There is also a shadow transport mechanism that can be used to take copies of
+messages that are successfully delivered by local transports, one copy per
+delivery. This could be used, $it{inter alia}, to implement automatic
+notification of delivery by sites that insist on doing such things.
+
+
+.section Intermittently connected hosts
+.index intermittently connected hosts
+It has become quite common (because it is cheaper) for hosts to connect to the
+Internet periodically rather than remain connected all the time. The normal
+arrangement is that mail for such hosts accumulates on a system that is
+permanently connected.
+
+Exim was designed for use on permanently connected hosts, and so it is not
+particularly well-suited to use in an intermittently connected environment.
+Nevertheless there are some features that can be used.
+
+.section Exim on the upstream server host
+It is tempting to arrange for incoming mail for the intermittently connected
+host to remain on Exim's queue until the client connects. However, this
+approach does not scale very well. Two different kinds of waiting message are
+being mixed up in the same queue -- those that cannot be delivered because of
+some temporary problem, and those that are waiting for their destination host
+to connect. This makes it hard to manage the queue, as well as wasting
+resources, because each queue runner scans the entire queue.
+
+A better approach is to separate off those messages that are waiting for an
+intermittently connected host. This can be done by delivering these messages
+into local files in batch SMTP, `mailstore', or other envelope-preserving
+format, from where they are transmitted by other software when their
+destination connects. This makes it easy to collect all the mail for one host
+in a single directory, and to apply local timeout rules on a per-message basis
+if required.
+
+On a very small scale, leaving the mail on Exim's queue can be made to work. If
+you are doing this, you should configure Exim with a long retry period for the
+intermittent host. For example:
+.display
+cheshire.wonderland.fict.example * F,5d,24h
+.endd
+This stops a lot of failed delivery attempts from occurring, but Exim remembers
+which messages it has queued up for that host. Once the intermittent host comes
+online, forcing delivery of one message (either by using the \-M-\ or \-R-\
+options, or by using the \\ETRN\\ SMTP command (see section ~~SECTETRN)
+causes all the queued up messages to be delivered, often down a single SMTP
+connection. While the host remains connected, any new messages get delivered
+immediately.
+
+If the connecting hosts do not have fixed IP addresses, that is, if a host is
+issued with a different IP address each time it connects, Exim's retry
+mechanisms on the holding host get confused, because the IP address is normally
+used as part of the key string for holding retry information. This can be
+avoided by unsetting \retry__include__ip__address\ on the \%smtp%\ transport.
+Since this has disadvantages for permanently connected hosts, it is best to
+arrange a separate transport for the intermittently connected ones.
+
+
+.section Exim on the intermittently connected client host
+The value of \smtp@_accept@_queue@_per@_connection\ should probably be
+increased, or even set to zero (that is, disabled) on the intermittently
+connected host, so that all incoming messages down a single connection get
+delivered immediately.
+
+.index SMTP||passed connection
+.index SMTP||multiple deliveries
+.index multiple SMTP deliveries
+Mail waiting to be sent from an intermittently connected host will probably
+not have been routed, because without a connection DNS lookups are not
+possible. This means that if a normal queue run is done at connection time,
+each message is likely to be sent in a separate SMTP session. This can be
+avoided by starting the queue run with a command line option beginning with
+\-qq-\ instead of \-q-\. In this case, the queue is scanned twice. In the first
+pass, routing is done but no deliveries take place. The second pass is a normal
+queue run; since all the messages have been previously routed, those destined
+for the same host are likely to get sent as multiple deliveries in a single
+SMTP connection.
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter SMTP processing
+.set runningfoot "smtp processing"
+.rset CHAPSMTP ~~chapter
+.index SMTP||processing details
+.index LMTP||processing details
+Exim supports a number of different ways of using the SMTP protocol, and its
+LMTP variant, which is an interactive protocol for transferring messages into a
+closed mail store application. This chapter contains details of how SMTP is
+processed. For incoming mail, the following are available:
+.numberpars $.
+SMTP over TCP/IP (Exim daemon or \*inetd*\);
+.nextp
+SMTP over the standard input and output (the \-bs-\ option);
+.nextp
+Batched SMTP on the standard input (the \-bS-\ option).
+.endp
+For mail delivery, the following are available:
+.numberpars $.
+SMTP over TCP/IP (the \%smtp%\ transport);
+.nextp
+LMTP over TCP/IP (the \%smtp%\ transport with the \protocol\ option set to
+`lmtp');
+.nextp
+LMTP over a pipe to a process running in the local host (the \%lmtp%\
+transport);
+.nextp
+Batched SMTP to a file or pipe (the \%appendfile%\ and \%pipe%\ transports with
+the \use@_bsmtp\ option set).
+.endp
+\*Batched SMTP*\ is the name for a process in which batches of messages are
+stored in or read from files (or pipes), in a format in which SMTP commands are
+used to contain the envelope information.
+
+
+.section Outgoing SMTP and LMTP over TCP/IP
+.rset SECToutSMTPTCP "~~chapter.~~section"
+.index SMTP||outgoing over TCP/IP
+.index outgoing SMTP over TCP/IP
+.index LMTP||over TCP/IP
+.index outgoing LMTP over TCP/IP
+.index \\EHLO\\
+.index \\HELO\\
+.index \\SIZE\\ option on \\MAIL\\ command
+Outgoing SMTP and LMTP over TCP/IP is implemented by the \%smtp%\ transport.
+The \protocol\ option selects which protocol is to be used, but the actual
+processing is the same in both cases.
+
+If, in response to its \\EHLO\\ command, Exim is told that the \\SIZE\\
+parameter is supported, it adds \\SIZE\\=<<n>> to each subsequent \\MAIL\\
+command. The value of <<n>> is the message size plus the value of the
+\size@_addition\ option (default 1024) to allow for additions to the message
+such as per-transport header lines, or changes made in a
+.index transport||filter
+.index filter||transport filter
+transport filter. If \size@_addition\ is set negative, the use of \\SIZE\\ is
+suppressed.
+
+If the remote server advertises support for \\PIPELINING\\, Exim uses the
+pipelining extension to SMTP (RFC 2197) to reduce the number of TCP/IP packets
+required for the transaction.
+
+If the remote server advertises support for the \\STARTTLS\\ command, and Exim
+was built to support TLS encryption, it tries to start a TLS session unless the
+server matches \hosts@_avoid@_tls\. See chapter ~~CHAPTLS for more details.
+
+If the remote server advertises support for the \\AUTH\\ command, Exim scans
+the authenticators configuration for any suitable client settings, as described
+in chapter ~~CHAPSMTPAUTH.
+
+.index carriage return
+.index linefeed
+Responses from the remote host are supposed to be terminated by CR followed by
+LF. However, there are known to be hosts that do not send CR characters, so in
+order to be able to interwork with such hosts, Exim treats LF on its own as a
+line terminator.
+
+If a message contains a number of different addresses, all those with the same
+characteristics (for example, the same envelope sender) that resolve to the
+same set of hosts, in the same order, are sent in a single SMTP transaction,
+even if they are for different domains, unless there are more than the setting
+of the \max@_rcpts\ option in the \%smtp%\ transport allows, in which case they
+are split into groups containing no more than \max@_rcpts\ addresses each. If
+\remote@_max@_parallel\ is greater than one, such groups may be sent in
+parallel sessions. The order of hosts with identical MX values is not
+significant when checking whether addresses can be batched in this way.
+
+When the \%smtp%\ transport suffers a temporary failure that is not
+message-related, Exim updates its transport-specific database, which contains
+records indexed by host name that remember which messages are waiting for each
+particular host. It also updates the retry database with new retry times.
+.index hints database||retry keys
+Exim's retry hints are based on host name plus IP address, so if one address of
+a multi-homed host is broken, it will soon be skipped most of the time.
+See the next section for more detail about error handling.
+
+.index SMTP||passed connection
+.index SMTP||batching over TCP/IP
+When a message is successfully delivered over a TCP/IP SMTP connection, Exim
+looks in the hints database for the transport to see if there are any queued
+messages waiting for the host to which it is connected. If it finds one, it
+creates a new Exim process using the \-MC-\ option (which can only be used by a
+process running as root or the Exim user) and passes the TCP/IP socket to it so
+that it can deliver another message using the same socket. The new process does
+only those deliveries that are routed to the connected host, and may in turn
+pass the socket on to a third process, and so on.
+
+The \connection@_max@_messages\ option of the \%smtp%\ transport can be used to
+limit the number of messages sent down a single TCP/IP connection.
+.index asterisk||after IP address
+The second and subsequent messages delivered down an existing connection are
+identified in the main log by the addition of an asterisk after the closing
+square bracket of the IP address.
+
+
+
+.section Errors in outgoing SMTP
+.rset SECToutSMTPerr "~~chapter.~~section"
+.index error||in outgoing SMTP
+.index SMTP||errors in outgoing
+.index host||error
+Three different kinds of error are recognized for outgoing SMTP: host errors,
+message errors, and recipient errors.
+.numberpars
+A host error is not associated with a particular message or with a
+particular recipient of a message. The host errors are:
+.numberpars $.
+Connection refused or timed out,
+.nextp
+Any error response code on connection,
+.nextp
+Any error response code to \\EHLO\\ or \\HELO\\,
+.nextp
+Loss of connection at any time, except after `.',
+.nextp
+I/O errors at any time,
+.nextp
+Timeouts during the session, other than in response to \\MAIL\\, \\RCPT\\ or
+the `.' at the end of the data.
+.endp
+For a host error, a permanent error response on connection, or in response to
+\\EHLO\\, causes all addresses routed to the host to be failed. Any other host
+error causes all addresses to be deferred, and retry data to be created for the
+host. It is not tried again, for any message, until its retry time arrives. If
+the current set of addresses are not all delivered in this run (to some
+alternative host), the message is added to the list of those waiting for this
+host, so if it is still undelivered when a subsequent successful delivery is
+made to the host, it will be sent down the same SMTP connection.
+.nextp
+.index message||error
+A message error is associated with a particular message when sent to a
+particular host, but not with a particular recipient of the message. The
+message errors are:
+.numberpars $.
+Any error response code to \\MAIL\\, \\DATA\\, or the `.' that terminates
+the data,
+.nextp
+Timeout after \\MAIL\\,
+.nextp
+Timeout
+or loss of connection after the `.' that terminates the data. A timeout after
+the \\DATA\\ command itself is treated as a host error, as is loss of
+connection at any other time.
+.endp
+For a message error, a permanent error response (5$it{xx}) causes all addresses
+to be failed, and a delivery error report to be returned to the sender. A
+temporary error response (4$it{xx}), or one of the timeouts, causes all
+addresses to be deferred. Retry data is not created for the host, but instead,
+a retry record for the combination of host plus message id is created. The
+message is not added to the list of those waiting for this host. This ensures
+that the failing message will not be sent to this host again until the retry
+time arrives. However, other messages that are routed to the host are not
+affected, so if it is some property of the message that is causing the error,
+it will not stop the delivery of other mail.
+
+If the remote host specified support for the \\SIZE\\ parameter in its response
+to \\EHLO\\, Exim adds SIZE=$it{nnn} to the \\MAIL\\ command, so an
+over-large message will cause a message error because the error arrives as a
+response to \\MAIL\\.
+.nextp
+.index recipient||error
+A recipient error is associated with a particular recipient of a message. The
+recipient errors are:
+.numberpars $.
+Any error response to \\RCPT\\,
+.nextp
+Timeout after \\RCPT\\.
+.endp
+For a recipient error, a permanent error response (5$it{xx}) causes the
+recipient address to be failed, and a bounce message to be returned to the
+sender. A temporary error response (4$it{xx}) or a timeout causes the failing
+address to be deferred, and routing retry data to be created for it. This is
+used to delay processing of the address in subsequent queue runs, until its
+routing retry time arrives. This applies to all messages, but because it
+operates only in queue runs, one attempt will be made to deliver a new message
+to the failing address before the delay starts to operate. This ensures that,
+if the failure is really related to the message rather than the recipient
+(`message too big for this recipient' is a possible example), other messages
+have a chance of getting delivered. If a delivery to the address does succeed,
+the retry information gets cleared, so all stuck messages get tried again, and
+the retry clock is reset.
+
+The message is not added to the list of those waiting for this host. Use of the
+host for other messages is unaffected, and except in the case of a timeout,
+other recipients are processed independently, and may be successfully delivered
+in the current SMTP session. After a timeout it is of course impossible to
+proceed with the session, so all addresses get deferred. However, those other
+than the one that failed do not suffer any subsequent retry delays. Therefore,
+if one recipient is causing trouble, the others have a chance of getting
+through when a subsequent delivery attempt occurs before the failing
+recipient's retry time.
+.endp
+
+In all cases, if there are other hosts (or IP addresses) available for the
+current set of addresses (for example, from multiple MX records), they are
+tried in this run for any undelivered addresses, subject of course to their
+own retry data. In other words, recipient error retry data does not take effect
+until the next delivery attempt.
+
+Some hosts have been observed to give temporary error responses to every
+\\MAIL\\ command at certain times (`insufficient space' has been seen). It
+would be nice if such circumstances could be recognized, and defer data for the
+host itself created, but this is not possible within the current Exim design.
+What actually happens is that retry data for every (host, message) combination
+is created.
+
+The reason that timeouts after \\MAIL\\ and \\RCPT\\ are treated specially is
+that these can sometimes arise as a result of the remote host's verification
+procedures. Exim makes this assumption, and treats them as if a temporary error
+response had been received. A timeout after `.' is treated specially because it
+is known that some broken implementations fail to recognize the end of the
+message if the last character of the last line is a binary zero. Thus, it is
+helpful to treat this case as a message error.
+
+Timeouts at other times are treated as host errors, assuming a problem with the
+host, or the connection to it. If a timeout after \\MAIL\\, \\RCPT\\,
+or `.' is really a connection problem, the assumption is that at the next try
+the timeout is likely to occur at some other point in the dialogue, causing it
+then to be treated as a host error.
+
+There is experimental evidence that some MTAs drop the connection after the
+terminating `.' if they do not like the contents of the message for some
+reason, in contravention of the RFC, which indicates that a 5$it{xx} response
+should be given. That is why Exim treats this case as a message rather than a
+host error, in order not to delay other messages to the same host.
+
+
+
+
+.section Variable Envelope Return Paths (VERP)
+.index VERP
+.index Variable Envelope Return Paths
+.index envelope sender
+Variable Envelope Return Paths -- see
+\?ftp://koobera.math.uic.edu/www/proto/verp.txt?\ -- can be supported in Exim
+by using the \return@_path\ generic transport option to rewrite the return path
+at transport time. For example, the following could be used on an \%smtp%\
+transport:
+.display asis
+return_path = \
+ ${if match {$return_path}{^(.+?)-request@your.dom.example\$}\
+ {$1-request=$local_part%$domain@your.dom.example}fail}
+.endd
+This has the effect of rewriting the return path (envelope sender) on all
+outgoing SMTP messages, if the local part of the original return path ends in
+`-request', and the domain is \*your.dom.example*\. The rewriting inserts the
+local part and domain of the recipient into the return path. Suppose, for
+example, that a message whose return path has been set to
+\*somelist-request@@your.dom.example*\ is sent to
+\*subscriber@@other.dom.example*\. In the transport, the return path is
+rewritten as
+.display asis
+somelist-request=subscriber%other.dom.example@your.dom.example
+.endd
+For this to work, you must arrange for outgoing messages that have `-request'
+in their return paths to have just a single recipient. This can be done by
+setting
+.display asis
+max_rcpt = 1
+.endd
+in the \%smtp%\ transport. Otherwise a single copy of a message might be
+addressed to several different recipients in the same domain, in which case
+\$local@_part$\ is not available (because it is not unique). Of course, if you
+do start sending out messages with this kind of return path, you must also
+configure Exim to accept the bounce messages that come back to those paths.
+Typically this would be done by setting an \local@_part@_suffix\ option for a
+suitable router.
+
+The overhead incurred in using VERP depends very much on the size of the
+message, the number of recipient addresses that resolve to the same remote
+host, and the speed of the connection over which the message is being sent. If
+a lot of addresses resolve to the same host and the connection is slow, sending
+a separate copy of the message for each address may take substantially longer
+than sending a single copy with many recipients (for which VERP cannot be
+used).
+
+
+.section Incoming SMTP messages over TCP/IP
+.index SMTP||incoming over TCP/IP
+.index incoming SMTP over TCP/IP
+.index inetd
+.index daemon
+Incoming SMTP messages can be accepted in one of two ways: by running a
+listening daemon, or by using \*inetd*\. In the latter case, the entry in
+\(/etc/inetd.conf)\ should be like this:
+.display asis
+smtp stream tcp nowait exim /opt/exim/bin/exim in.exim -bs
+.endd
+Exim distinguishes between this case and the case of a locally running user
+agent using the \-bs-\ option by checking whether or not the standard input is
+a socket. When it is, either the port must be privileged (less than 1024), or
+the caller must be root or the Exim user. If any other user passes a socket
+with an unprivileged port number, Exim prints a message on the standard error
+stream and exits with an error code.
+
+By default, Exim does not make a log entry when a remote host connects or
+disconnects (either via the daemon or \*inetd*\), unless the disconnection is
+unexpected. It can be made to write such log entries by setting the
+\smtp@_connection\ log selector.
+
+.index carriage return
+.index linefeed
+Commands from the remote host are supposed to be terminated by CR followed by
+LF. However, there are known to be hosts that do not send CR characters. In
+order to be able to interwork with such hosts, Exim treats LF on its own as a
+line terminator.
+Furthermore, because common code is used for receiving messages from all
+sources, a CR on its own is also interpreted as a line terminator. However, the
+sequence `CR, dot, CR' does not terminate incoming SMTP data.
+
+.index \\EHLO\\||invalid data
+.index \\HELO\\||invalid data
+One area that sometimes gives rise to problems concerns the \\EHLO\\ or
+\\HELO\\ commands. Some clients send syntactically invalid versions of these
+commands, which Exim rejects by default. (This is nothing to do with verifying
+the data that is sent, so \helo@_verify@_hosts\ is not relevant.) You can tell
+Exim not to apply a syntax check by setting \helo@_accept@_junk@_hosts\ to
+match the broken hosts that send invalid commands.
+
+.index \\SIZE\\ option on \\MAIL\\ command
+.index \\MAIL\\||\\SIZE\\ option
+The amount of disk space available is checked whenever \\SIZE\\ is received on
+a \\MAIL\\ command, independently of whether \message@_size@_limit\ or
+\check@_spool@_space\ is configured, unless \smtp__check__spool__space\ is set
+false. A temporary error is given if there is not enough space. If
+\check@_spool@_space\ is set, the check is for that amount of space plus the
+value given with \\SIZE\\, that is, it checks that the addition of the incoming
+message will not reduce the space below the threshold.
+
+When a message is successfully received, Exim includes the local message id in
+its response to the final `.' that terminates the data. If the remote host logs
+this text it can help with tracing what has happened to a message.
+
+The Exim daemon can limit the number of simultaneous incoming connections it is
+prepared to handle (see the \smtp@_accept@_max\ option). It can also limit the
+number of simultaneous incoming connections from a single remote host (see the
+\smtp@_accept@_max@_per@_host\ option). Additional connection attempts are
+rejected using the SMTP temporary error code 421.
+
+The Exim daemon does not rely on the \\SIGCHLD\\ signal to detect when a
+subprocess has finished, as this can get lost at busy times. Instead, it looks
+for completed subprocesses every time it wakes up. Provided there are other
+things happening (new incoming calls, starts of queue runs), completed
+processes will be noticed and tidied away. On very quiet systems you may
+sometimes see a `defunct' Exim process hanging about. This is not a problem; it
+will be noticed when the daemon next wakes up.
+
+When running as a daemon, Exim can reserve some SMTP slots for specific hosts,
+and can also be set up to reject SMTP calls from non-reserved hosts at times of
+high system load -- for details see the \smtp@_accept@_reserve\,
+\smtp@_load@_reserve\, and \smtp@_reserve@_hosts\ options. The load check
+applies in both the daemon and \*inetd*\ cases.
+
+Exim normally starts a delivery process for each message received, though this
+can be varied by means of the \-odq-\ command line option and the
+\queue@_only\, \queue@_only@_file\, and \queue@_only@_load\ options. The number
+of simultaneously running delivery processes started in this way from SMTP
+input can be limited by the \smtp__accept__queue\ and
+\smtp__accept__queue__per__connection\ options. When either limit is reached,
+subsequently received messages are just put on the input queue without starting
+a delivery process.
+
+The controls that involve counts of incoming SMTP calls (\smtp@_accept@_max\,
+\smtp@_accept@_queue\, \smtp__accept__reserve\) are not available when Exim is
+started up from the \*inetd*\ daemon, because in that case each connection is
+handled by an entirely independent Exim process. Control by load average is,
+however, available with \*inetd*\.
+
+Exim can be configured to verify addresses in incoming SMTP commands as they
+are received. See chapter ~~CHAPACL for details. It can also be configured to
+rewrite addresses at this time -- before any syntax checking is done. See
+section ~~SECTrewriteS.
+
+Exim can also be configured to limit the rate at which a client host submits
+\\MAIL\\ and \\RCPT\\ commands in a single SMTP session. See the
+\smtp@_ratelimit@_hosts\ option.
+
+
+.section Unrecognized SMTP commands
+.index SMTP||unrecognized commands
+If Exim receives more than \smtp@_max@_unknown@_commands\ unrecognized SMTP
+commands during a single SMTP connection, it drops the connection after sending
+the error response to the last command. The default value for
+\smtp@_max@_unknown@_commands\ is 3. This is a defence against some kinds of
+abuse that subvert web servers into making connections to SMTP ports; in these
+circumstances, a number of non-SMTP lines are sent first.
+
+.section Syntax and protocol errors in SMTP commands
+.index SMTP||syntax errors
+.index SMTP||protocol errors
+A syntax error is detected if an SMTP command is recognized, but there is
+something syntactically wrong with its data, for example, a malformed email
+address in a \\RCPT\\ command. Protocol errors include invalid command
+sequencing such as \\RCPT\\ before \\MAIL\\. If Exim receives more than
+\smtp@_max@_synprot@_errors\ such commands during a single SMTP connection, it
+drops the connection after sending the error response to the last command. The
+default value for \smtp__max__synprot__errors\ is 3. This is a defence against
+broken clients that loop sending bad commands (yes, it has been seen).
+
+
+.section Use of non-mail SMTP commands
+.index SMTP||non-mail commands
+The `non-mail' SMTP commands are those other than \\MAIL\\, \\RCPT\\, and
+\\DATA\\. Exim counts such commands, and drops the connection if there are too
+many of them in a single SMTP session. This action catches some
+denial-of-service attempts and things like repeated failing \\AUTH\\s, or a mad
+client looping sending \\EHLO\\. The global option \smtp@_accept@_max@_nonmail\
+defines what `too many' means. Its default value is 10.
+
+When a new message is expected, one occurrence of \\RSET\\ is not counted. This
+allows a client to send one \\RSET\\ between messages (this is not necessary,
+but some clients do it). Exim also allows one uncounted occurence of \\HELO\\
+or \\EHLO\\, and one occurrence of \\STARTTLS\\ between messages. After
+starting up a TLS session, another \\EHLO\\ is expected, and so it too is not
+counted.
+
+The first occurrence of \\AUTH\\ in a connection, or immediately following
+\\STARTTLS\\ is also not counted. Otherwise, all commands other than \\MAIL\\,
+\\RCPT\\, \\DATA\\, and \\QUIT\\ are counted.
+
+You can control which hosts are subject to the limit set by
+\smtp@_accept@_max@_nonmail\ by setting
+\smtp@_accept@_max@_nonmail@_hosts\. The default value is \"$*$"\, which makes
+the limit apply to all hosts. This option means that you can exclude any
+specific badly-behaved hosts that you have to live with.
+
+
+
+.section The \\VRFY\\ and \\EXPN\\ commands
+When Exim receives a \\VRFY\\ or \\EXPN\\ command on a TCP/IP connection, it
+runs the ACL specified by \acl@_smtp@_vrfy\ or \acl@_smtp@_expn\ (as
+appropriate) in order to decide whether the command should be accepted or not.
+If no ACL is defined, the command is rejected.
+
+.index \\VRFY\\||processing
+When \\VRFY\\ is accepted, it runs exactly the same code as when Exim is
+called with the \-bv-\ option.
+.index \\EXPN\\||processing
+When \\EXPN\\ is accepted, a single-level expansion of the address is done.
+\\EXPN\\ is treated as an `address test' (similar to the \-bt-\ option) rather
+than a verification (the \-bv-\ option). If an unqualified local part is given
+as the argument to \\EXPN\\, it is qualified with \qualify@_domain\. Rejections
+of \\VRFY\\ and \\EXPN\\ commands are logged on the main and reject logs, and
+\\VRFY\\ verification failures are logged on the main log for consistency with
+\\RCPT\\ failures.
+
+
+.section The \\ETRN\\ command
+.rset SECTETRN "~~chapter.~~section"
+.index \\ETRN\\||processing
+RFC 1985 describes an SMTP command called \\ETRN\\ that is designed to
+overcome the security problems of the \\TURN\\ command (which has fallen into
+disuse). When Exim receives an \\ETRN\\ command on a TCP/IP connection, it runs
+the ACL specified by \acl@_smtp@_etrn\ in order to decide whether the command
+should be accepted or not. If no ACL is defined, the command is rejected.
+
+The \\ETRN\\ command is concerned with `releasing' messages that are awaiting
+delivery to certain hosts. As Exim does not organize its message queue by host,
+the only form of \\ETRN\\ that is supported by default is the one where the
+text starts with the `@#' prefix, in which case the remainder of the text is
+specific to the SMTP server. A valid \\ETRN\\ command causes a run of Exim with
+the \-R-\ option to happen, with the remainder of the \\ETRN\\ text as its
+argument. For example,
+.display asis
+ETRN #brigadoon
+.endd
+runs the command
+.display asis
+exim -R brigadoon
+.endd
+which causes a delivery attempt on all messages with undelivered addresses
+containing the text `brigadoon'. When \smtp@_etrn@_serialize\ is set (the
+default), Exim prevents the simultaneous execution of more than one queue run
+for the same argument string as a result of an \\ETRN\\ command. This stops
+a misbehaving client from starting more than one queue runner at once.
+
+.index hints database||\\ETRN\\ serialization
+Exim implements the serialization by means of a hints database in which a
+record is written whenever a process is started by \\ETRN\\, and deleted when
+the process completes. However, Exim does not keep the SMTP session waiting for
+the \\ETRN\\ process to complete. Once \\ETRN\\ is accepted, the client is sent
+a `success' return code. Obviously there is scope for hints records to get left
+lying around if there is a system or program crash. To guard against this, Exim
+ignores any records that are more than six hours old.
+
+.index \smtp@_etrn@_command\
+For more control over what \\ETRN\\ does, the \smtp@_etrn@_command\ option can
+used. This specifies a command that is run whenever \\ETRN\\ is received,
+whatever the form of its argument. For
+example:
+.display asis
+smtp_etrn_command = /etc/etrn_command $domain $sender_host_address
+.endd
+The string is split up into arguments which are independently expanded. The
+expansion variable \$domain$\ is set to the argument of the \\ETRN\\ command,
+and no syntax checking is done on the contents of this argument. Exim does not
+wait for the command to complete, so its status code is not checked. Exim runs
+under its own uid and gid when receiving incoming SMTP, so it is not possible
+for it to change them before running the command.
+
+
+.section Incoming local SMTP
+.index SMTP||local incoming
+Some user agents use SMTP to pass messages to their local MTA using the
+standard input and output, as opposed to passing the envelope on the command
+line and writing the message to the standard input. This is supported by the
+\-bs-\ option. This form of SMTP is handled in the same way as incoming
+messages over TCP/IP (including the use of ACLs), except that the envelope
+sender given in a \\MAIL\\ command is ignored unless the caller is trusted. In
+an ACL you can detect this form of SMTP input by testing for an empty host
+identification. It is common to have this as the first line in the ACL that
+runs for \\RCPT\\ commands:
+.display asis
+accept hosts = :
+.endd
+This accepts SMTP messages from local processes without doing any other tests.
+
+
+.section Outgoing batched SMTP
+.rset SECTbatchSMTP "~~chapter.~~section"
+.index SMTP||batched outgoing
+.index batched SMTP output
+Both the \%appendfile%\ and \%pipe%\ transports can be used for handling batched
+SMTP. Each has an option called \use@_bsmtp\ which causes messages to be output
+in BSMTP format. No SMTP responses are possible for this form of delivery. All
+it is doing is using SMTP commands as a way of transmitting the envelope along
+with the message.
+
+The message is written to the file or pipe preceded by the SMTP commands
+\\MAIL\\ and \\RCPT\\, and followed by a line containing a single dot. Lines in
+the message that start with a dot have an extra dot added. The SMTP command
+\\HELO\\ is not normally used. If it is required, the \message@_prefix\ option
+can be used to specify it.
+
+Because \%appendfile%\ and \%pipe%\ are both local transports, they accept only
+one recipient address at a time by default. However, you can arrange for them
+to handle several addresses at once by setting the \batch@_max\ option. When
+this is done for BSMTP, messages may contain multiple \\RCPT\\ commands. See
+chapter ~~CHAPbatching for more details.
+
+When one or more addresses are routed to a BSMTP transport by a router that
+sets up a host list, the name of the first host on the list is available to the
+transport in the variable \$host$\. Here is an example of such a transport and
+router:
+.display asis
+begin routers
+route_append:
+ driver = manualroute
+ transport = smtp_appendfile
+ route_list = domain.example batch.host.example
+
+begin transports
+smtp_appendfile:
+ driver = appendfile
+ directory = /var/bsmtp/$host
+ batch_max = 1000
+ use_bsmtp
+ user = exim
+.endd
+This causes messages addressed to \*domain.example*\ to be written in BSMTP
+format to \(/var/bsmtp/batch.host.example)\, with only a single copy of each
+message (unless there are more than 1000 recipients).
+
+
+.section Incoming batched SMTP
+.rset SECTincomingbatchedSMTP "~~chapter.~~section"
+.index SMTP||batched incoming
+.index batched SMTP input
+The \-bS-\ command line option causes Exim to accept one or more messages by
+reading SMTP on the standard input, but to generate no responses. If the caller
+is trusted, the senders in the \\MAIL\\ commands are believed; otherwise the
+sender is always the caller of Exim. Unqualified senders and receivers are not
+rejected (there seems little point) but instead just get qualified. \\HELO\\
+and \\EHLO\\ act as \\RSET\\; \\VRFY\\, \\EXPN\\, \\ETRN\\ and \\HELP\\, act
+as \\NOOP\\; \\QUIT\\ quits.
+
+No policy checking is done for BSMTP input. That is, no ACL is run at anytime.
+In this respect it is like non-SMTP local input.
+
+If an error is detected while reading a message, including a missing `.' at
+the end, Exim gives up immediately. It writes details of the error to the
+standard output in a stylized way that the calling program should be able to
+make some use of automatically, for example:
+.display asis
+554 Unexpected end of file
+Transaction started in line 10
+Error detected in line 14
+.endd
+It writes a more verbose version, for human consumption, to the standard error
+file, for example:
+.display asis
+An error was detected while processing a file of BSMTP input.
+The error message was:
+
+ 501 '>' missing at end of address
+
+The SMTP transaction started in line 10.
+The error was detected in line 12.
+The SMTP command at fault was:
+
+ rcpt to:<malformed@in.com.plete
+
+1 previous message was successfully processed.
+The rest of the batch was abandoned.
+.endd
+The return code from Exim is zero only if there were no errors. It is 1 if some
+messages were accepted before an error was detected, and 2 if no messages were
+accepted.
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Message processing
+.set runningfoot "message processing"
+.rset CHAPmsgproc "~~chapter"
+.index message||general processing
+Exim performs various transformations on the sender and recipient addresses of
+all messages that it handles, and also on the messages' header lines. Some of
+these are optional and configurable, while others always take place. All of
+this processing, except rewriting as a result of routing, and the addition or
+removal of header lines while delivering, happens when a message is received,
+before it is placed on Exim's queue.
+
+Some of the automatic processing takes place
+.em
+by default
+.nem
+only for `locally-originated' messages. This adjective is used to describe
+messages that are not received over TCP/IP, but instead are passed to an Exim
+process on its standard input. This includes the interactive `local SMTP' case
+that is set up by the \-bs-\ command line option. \**Note**\: messages received
+over TCP/IP on the loopback interface (127.0.0.1 or @:@:1) are not considered
+to be locally-originated. Exim does not treat the loopback interface specially
+in any way.
+
+.em
+.index message||submission
+Processing that happens automatically for locally-originated messages can also
+be requested for other messages. This is done by obeying the modifier
+.display asis
+control = submission
+.endd
+in one of the ACLs that are run for an incoming message (see section
+~~SECTACLmodi). This makes Exim treat the message as a local submission, and is
+normally used when the source of the message is known to be an MUA running on a
+client host (as opposed to an MTA). In the descriptions below, the term
+`submission mode' is used to describe this state.
+
+When a ::From:: or ::Sender:: header is generated in submission mode, the value
+of \qualify@_domain\ is used by default. However, it is possible to specify
+another domain by a setting such as
+.display asis
+control = submission/domain=some.other.domain
+.endd
+.nem
+
+
+
+.section Line endings
+.rset SECTlineendings "~~chapter.~~section"
+.index line endings
+.index carriage return
+.index linefeed
+RFC 2821 specifies that CRLF (two characters: carriage-return, followed by
+linefeed) is the line ending for messages transmitted over the Internet using
+SMTP over TCP/IP. However, within individual operating systems, different
+conventions are used. For example, Unix-like systems use just LF, but others
+use CRLF or just CR.
+
+Exim was designed for Unix-like systems, and internally, it stores messages
+using the system's convention of a single LF as a line terminator. When
+receiving a message, all line endings are translated to this standard format.
+Originally, it was thought that programs that passed messages directly to an
+MTA within an operating system would use that system's convention. Experience
+has shown that this is not the case; for example, there are Unix applications
+that use CRLF in this circumstance. For this reason, and for compatibility with
+other MTAs, the way Exim handles line endings for all messages is now as
+follows:
+.numberpars $.
+LF not preceded by CR is treated as a line ending.
+.nextp
+CR is treated as a line ending; if it is immediately followed by LF, the LF
+is ignored.
+.nextp
+The sequence `CR, dot, CR' does not terminate an incoming SMTP message,
+nor a local message in the state where a line containing only a dot is a
+terminator.
+.nextp
+If a bare CR is encountered within a header line, an extra space is added after
+the line terminator so as not to end the header line. The reasoning behind this
+is that bare CRs in header lines are most likely either to be mistakes, or
+people trying to play silly games.
+.nextp
+.em
+If the first header line received in a message ends with CRLF, a subsequent
+bare LF in a header line is treated in the same way as a bare CR in a header
+line.
+.nem
+.endp
+
+
+
+.section Unqualified addresses
+.index unqualified addresses
+.index address||qualification
+By default, Exim expects every address it receives from an external host to be
+fully qualified. Unqualified addresses cause negative responses to SMTP
+commands. However, because SMTP is used as a means of transporting messages
+from MUAs running on personal workstations, there is sometimes a requirement to
+accept unqualified addresses from specific hosts or IP networks.
+
+Exim has two options that separately control which hosts may send unqualified
+sender or receipient addresses in SMTP commands, namely
+\sender__unqualified__hosts\ and \recipient__unqualified__hosts\. In both
+cases, if an unqualified address is accepted, it is qualified by adding the
+value of \qualify__domain\ or \qualify__recipient\, as appropriate.
+.index \qualify@_domain\
+.index \qualify@_recipient\
+
+
+.section The UUCP From line
+.index `From' line
+.index UUCP||`From' line
+.index sender||address
+.index \uucp@_from@_pattern\
+.index \uucp@_from@_sender\
+.index envelope sender
+.index Sendmail compatibility||`From' line
+Messages that have come from UUCP (and some other applications) often begin
+with a line containing the envelope sender and a timestamp, following the word
+`From'. Examples of two common formats are:
+.display asis
+From a.oakley@berlin.mus Fri Jan 5 12:35 GMT 1996
+From f.butler@berlin.mus Fri, 7 Jan 97 14:00:00 GMT
+.endd
+This line precedes the RFC 2822 header lines. For compatibility with Sendmail,
+Exim recognizes such lines at the start of messages that are submitted to it
+via the command line (that is, on the standard input). It does not recognize
+such lines in incoming SMTP messages, unless the sending host matches
+\ignore@_fromline@_hosts\ or the \-bs-\ option was used for a local message and
+\ignore@_fromline@_local\ is set. The recognition is controlled by a regular
+expression that is defined by the \uucp@_from@_pattern\ option, whose default
+value matches the two common cases shown above and puts the address that
+follows `From' into \$1$\.
+
+.index numerical variables (\$1$\, \$2$\, etc)||in `From ' line handling
+When the caller of Exim for a non-SMTP message that contains a `From' line is a
+trusted user, the message's sender address is constructed by expanding the
+contents of \uucp@_sender@_address\, whose default value is `@$1'. This is then
+parsed as an RFC 2822 address. If there is no domain, the local part is
+qualified with \qualify@_domain\ unless it is the empty string. However, if the
+command line \-f-\ option is used, it overrides the `From' line.
+
+If the caller of Exim is not trusted, the `From' line is recognized, but the
+sender address is not changed. This is also the case for incoming SMTP messages
+that are permitted to contain `From' lines.
+
+Only one `From' line is recognized. If there is more than one, the second is
+treated as a data line that starts the body of the message, as it is not valid
+as a header line. This also happens if a `From' line is present in an incoming
+SMTP message from a source that is not permitted to send them.
+
+
+.section Resent- header lines
+.index \Resent@-\ header lines
+RFC 2822 makes provision for sets of header lines starting with the string
+\"Resent-"\ to be added to a message when it is resent by the original
+recipient to somebody else. These headers are ::Resent-Date::, ::Resent-From::,
+::Resent-Sender::, ::Resent-To::, ::Resent-Cc::, ::Resent-Bcc:: and
+::Resent-Message-ID::. The RFC says:
+
+\*Resent fields are strictly informational. They MUST NOT be used in the normal
+processing of replies or other such automatic actions on messages.*\
+
+This leaves things a bit vague as far as other processing actions such as
+address rewriting are concerned. Exim treats \Resent@-\ header lines as
+follows:
+.numberpars $.
+A ::Resent-From:: line that just contains the login id of the submitting user
+is automatically rewritten in the same way as ::From:: (see below).
+.nextp
+If there's a rewriting rule for a particular header line, it is also applied to
+\Resent@-\ header lines of the same type. For example, a rule that rewrites
+::From:: also rewrites ::Resent-From::.
+.nextp
+For local messages, if ::Sender:: is removed on input, ::Resent-Sender:: is also
+removed.
+.nextp
+For a locally-submitted message,
+if there are any \Resent@-\ header lines but no ::Resent-Date::,
+::Resent-From::, or ::Resent-Message-Id::, they are added as necessary. It is
+the contents of ::Resent-Message-Id:: (rather than ::Message-Id::) which are
+included in log lines in this case.
+.nextp
+The logic for adding ::Sender:: is duplicated for ::Resent-Sender:: when any
+\Resent@-\ header lines are present.
+.endp
+
+
+.section The Auto-Submitted: header line
+Whenever Exim generates a bounce or a delay warning message, it includes the
+header line
+.display asis
+Auto-Submitted: auto-generated
+.endd
+
+
+.section The Bcc: header line
+.index ::Bcc:: header line
+If Exim is called with the \-t-\ option, to take recipient addresses from a
+message's header, it removes any ::Bcc:: header line that may exist (after
+extracting its addresses). If \-t-\ is not present on the command line, any
+existing ::Bcc:: is not removed.
+
+.section The Date: header line
+.index ::Date:: header line
+If a locally-generated
+.em
+or submission-mode
+.nem
+message has no ::Date:: header line, Exim adds one, using the current date and
+time.
+
+.section The Delivery-date: header line
+.index ::Delivery-date:: header line
+.index \delivery@_date@_remove\
+::Delivery-date:: header lines are not part of the standard RFC 2822 header
+set. Exim can be configured to add them to the final delivery of messages. (See
+the generic \delivery@_date@_add\ transport option.) They should not be present
+in messages in transit. If the \delivery@_date@_remove\ configuration option is
+set (the default), Exim removes ::Delivery-date:: header lines from incoming
+messages.
+
+.section The Envelope-to: header line
+.index ::Envelope-to:: header line
+.index \envelope@_to@_remove\
+::Envelope-to:: header lines are not part of the standard RFC 2822 header set.
+Exim can be configured to add them to the final delivery of messages. (See the
+generic \envelope@_to@_add\ transport option.) They should not be present in
+messages in transit. If the \envelope@_to@_remove\ configuration option is set
+(the default), Exim removes ::Envelope-to:: header lines from incoming
+messages.
+
+.section The From: header line
+.index ::From:: header line
+.index Sendmail compatibility||`From' line
+.em
+If a submission-mode message does not contain a ::From:: header line, Exim adds
+one if either of the following conditions is true:
+.numberpars alpha
+The envelope sender address is not empty (that is, this is not a bounce
+message); the added header line copies the envelope sender address.
+.nextp
+The SMTP session is authenticated and \$authenticated@_id$\ is not empty; the
+added header's local part is \$authenticated@_id$\ and the domain is
+the domain specified on the submission control, or \$qualify@_domain$\ if that
+is not set.
+.endp
+A non-empty envelope sender takes precedence.
+.nem
+
+If a locally-generated incoming message does not contain a ::From:: header
+line, Exim adds one containing the sender's address. The calling user's login
+name and full name are used to construct the address, as described in section
+~~SECTconstr. They are obtained from the password data by calling
+\*getpwuid()*\ (but see the \unknown@_login\ configuration option). The address
+is qualified with \qualify@_domain\.
+
+For compatibility with Sendmail, if an incoming, non-SMTP message has a
+::From:: header line containing just the unqualified login name of the calling
+user, this is replaced by an address containing the user's login name and full
+name as described in section ~~SECTconstr.
+
+.section The Message-ID: header line
+.index ::Message-ID:: header line
+If a locally-generated
+.em
+or submission-mode
+.nem
+incoming message does not contain a ::Message-ID:: or ::Resent-Message-ID::
+header line, Exim adds one to the message. If there are any ::Resent-:: headers
+in the message, it creates ::Resent-Message-ID::. The id is constructed from
+Exim's internal message id, preceded by the letter E to ensure it starts with a
+letter, and followed by @@ and the primary host name. Additional information
+can be included in this header line by setting the
+.index \message@_id@_header@_text\
+\message@_id@_header@_text\ and/or \message__id__header__domain\ options.
+
+
+.section The Received: header line
+.index ::Received:: header line
+A ::Received:: header line is added at the start of every message. The contents
+are defined by the \received@_header@_text\ configuration option, and Exim
+automatically adds a semicolon and a timestamp to the configured string.
+
+.em
+The ::Received:: header is generated as soon as the message's header lines have
+been received. At this stage, the timestamp in the ::Received:: header line is
+the time that the message started to be received. This is the value that is
+seen by the \\DATA\\ ACL and by the \*local@_scan()*\ function.
+
+Once a message is accepted, the timestamp in the ::Received:: header line is
+changed to the time of acceptance, which is (apart from a small delay while the
+-H spool file is written) the earliest time at which delivery could start.
+.nem
+
+
+.section The Return-path: header line
+.index ::Return-path:: header line
+.index \return@_path@_remove\
+::Return-path:: header lines are defined as something an MTA may insert when
+it does the final delivery of messages. (See the generic \return@_path@_add\
+transport option.) Therefore, they should not be present in messages in
+transit. If the \return@_path@_remove\ configuration option is set (the
+default), Exim removes ::Return-path:: header lines from incoming messages.
+
+
+.section The Sender: header line
+.rset SECTthesenhea "~~chapter.~~section"
+.index ::Sender:: header line
+For a locally-originated message from an untrusted user, Exim may remove an
+existing ::Sender:: header line, and it may add a new one. You can modify these
+actions by setting \local@_sender@_retain\ true or \local@_from@_check\ false.
+
+When a local message is received from an untrusted user and
+\local@_from@_check\ is true (the default), a check is made to see if the
+address given in the ::From:: header line is the correct (local) sender of the
+message. The address that is expected has the login name as the local part and
+the value of \qualify@_domain\ as the domain. Prefixes and suffixes for the
+local part can be permitted by setting \local@_from@_prefix\ and
+\local@_from@_suffix\ appropriately. If ::From:: does not contain the correct
+sender, a ::Sender:: line is added to the message.
+
+If you set \local@_from@_check\ false, this checking does not occur. However,
+the removal of an existing ::Sender:: line still happens, unless you also set
+\local@_sender@_retain\ to be true. It is not possible to set both of these
+options true at the same time.
+
+.em
+By default, no processing of ::Sender:: header lines is done for messages
+received by TCP/IP or for messages submitted by trusted users. However, when a
+message is received over TCP/IP in submission mode, ::Sender:: header lines are
+always removed. If the SMTP session is authenticated, and \$authenticated@_id$\
+is not empty, a sender address is created with \$authenticated@_id$\ as the
+local part and either the domain specified in the submission control or, if
+that is not specified, \$qualify@_domain$\ as the domain. This is compared with
+the address in the ::From:: header line. If they are different, a ::Sender::
+header line is added. Prefixes and suffixes for the local part in ::From:: can
+be permitted by setting \local@_from@_prefix\ and \local@_from@_suffix\
+appropriately.
+.nem
+
+
+.section Adding and removing header lines
+.index header lines||adding
+.index header lines||removing
+.rset SECTheadersaddrem "~~chapter.~~section"
+When a message is delivered, the addition and removal of header lines can be
+specified on any of the routers and transports, and also in the system filter.
+Changes specified in the system filter affect all deliveries of a message.
+
+Header changes specified on a router affect all addresses handled by that
+router, and also any new addresses it generates. If an address passes through
+several routers, the changes are cumulative. When a message is processed by a
+transport, the message's original set of header lines is output, except for
+those named in any \headers@_remove\ options that the address has encountered
+as it was processed, and any in the transport's own \headers@_remove\ option.
+Then the new header lines from \headers@_add\ options are output.
+
+
+.section Constructed addresses
+.rset SECTconstr "~~chapter.~~section"
+.index address||constructed
+.index constructed address
+When Exim constructs a sender address for a locally-generated message, it uses
+the form
+.display
+<<user name>> <$$<<login>>@@<<qualify@_domain>>$$>
+.endd
+For example:
+.display asis
+Zaphod Beeblebrox <zaphod@end.univ.example>
+.endd
+The user name is obtained from the \-F-\ command line option if set, or
+otherwise by looking up the calling user by \*getpwuid()*\ and extracting the
+`gecos' field from the password entry. If the `gecos' field contains an
+ampersand character, this is replaced by the login name with the first letter
+upper cased, as is conventional in a number of operating systems. See the
+\gecos@_name\ option for a way to tailor the handling of the `gecos' field. The
+\unknown@_username\ option can be used to specify user names in cases when
+there is no password file entry.
+
+In all cases, the user name is made to conform to RFC 2822 by quoting all or
+parts of it if necessary. In addition, if it contains any non-printing
+characters, it is encoded as described in RFC 2047, which defines a way of
+including non-ASCII characters in header lines.
+The value of the \headers@_charset\ option specifies the name of the encoding
+that is used (the characters are assumed to be in this encoding).
+The setting of \print@_topbitchars\ controls whether characters with the top
+bit set (that is, with codes greater than 127) count as printing characters or
+not.
+
+
+.section Case of local parts
+.index case of local parts
+.index local part||case of
+RFC 2822 states that the case of letters in the local parts of addresses cannot
+be assumed to be non-significant. Exim preserves the case of local parts of
+addresses, but by default it uses a lower-cased form when it is routing,
+because on most Unix systems, usernames are in lower case and case-insensitive
+routing is required. However, any particular router can be made to use the
+original case for local parts by setting the \caseful@_local@_part\ generic
+router option.
+
+.index mixed-case login names
+If you must have mixed-case user names on your system, the best way to proceed,
+assuming you want case-independent handling of incoming email, is to set up
+your first router to convert incoming local parts in your domains to the
+correct case by means of a file lookup. For example:
+.display asis
+correct_case:
+ driver = redirect
+ domains = +local_domains
+ data = ${lookup{$local_part}cdb\
+ {/etc/usercased.cdb}{$value}fail}\
+ @$domain
+.endd
+For this router, the local part is forced to lower case by the default action
+(\caseful@_local@_part\ is not set). The lower-cased local part is used to look
+up a new local part in the correct case. If you then set \caseful@_local@_part\
+on any subsequent routers which process your domains, they will operate on
+local parts with the correct case in a case-sensitive manner.
+
+
+.section Dots in local parts
+.index dot||in local part
+.index local part||dots in
+RFC 2822 forbids empty components in local parts. That is, an unquoted local
+part may not begin or end with a dot, nor have two consecutive dots in the
+middle. However, it seems that many MTAs do not enforce this, so Exim permits
+empty components for compatibility.
+
+
+.section Rewriting addresses
+.index rewriting||addresses
+Rewriting of sender and recipient addresses, and addresses in headers, can
+happen automatically, or as the result of configuration options, as described
+in chapter ~~CHAPrewrite. The headers that may be affected by this are ::Bcc::,
+::Cc::, ::From::, ::Reply-To::, ::Sender::, and ::To::.
+
+Automatic rewriting includes qualification, as mentioned above. The other case
+in which it can happen is when an incomplete non-local domain is given. The
+routing process may cause this to be expanded into the full domain name. For
+example, a header such as
+.display asis
+To: hare@teaparty
+.endd
+might get rewritten as
+.display asis
+To: hare@teaparty.wonderland.fict.example
+.endd
+Rewriting as a result of routing is the one kind of message processing that
+does not happen at input time, as it cannot be done until the address has
+been routed.
+
+Strictly, one should not do $it{any} deliveries of a message until all its
+addresses have been routed, in case any of the headers get changed as a
+result of routing. However, doing this in practice would hold up many
+deliveries for unreasonable amounts of time, just because one address could not
+immediately be routed. Exim therefore does not delay other deliveries when
+routing of one or more addresses is deferred.
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Log files
+.set runningfoot "log files"
+.rset CHAPlog "~~chapter"
+.index log||types of
+.index log||general description
+Exim writes three different logs, referred to as the main log, the reject log,
+and the panic log:
+.numberpars $.
+.index main log
+The main log records the arrival of each message and each delivery in a single
+line in each case. The format is as compact as possible, in an attempt to keep
+down the size of log files. Two-character flag sequences make it easy to pick
+out these lines. A number of other events are recorded in the main log. Some of
+them are optional, in which case the \log@_selector\ option controls whether
+they are included or not. A Perl script called \*eximstats*\, which does simple
+analysis of main log files, is provided in the Exim distribution (see section
+~~SECTmailstat).
+.nextp
+.index reject log
+The reject log records information from messages that are rejected as a result
+of a configuration option (that is, for policy reasons).
+.em
+The first line of each rejection is a copy of the line that is also written to
+the main log. Then, if the message's header has been read at the time the log
+is written, its contents are written to this log. Only the original header
+lines are available; header lines added by ACLs are not logged. You can use the
+reject log to check that your policy controls are working correctly; on a busy
+host this may be easier than scanning the main log for rejection messages. You
+can suppress the writing of the reject log by setting \write@_rejectlog\ false.
+.nem
+.nextp
+.index panic log
+.index system log
+When certain serious errors occur, Exim writes entries to its panic log. If the
+error is sufficiently disastrous, Exim bombs out afterwards. Panic log entries
+are usually written to the main log as well, but can get lost amid the mass of
+other entries. The panic log should be empty under normal circumstances. It is
+therefore a good idea to check it (or to have a \*cron*\ script check it)
+regularly, in order to become aware of any problems. When Exim cannot open its
+panic log, it tries as a last resort to write to the system log (syslog). This
+is opened with LOG@_PID+LOG@_CONS and the facility code of LOG@_MAIL. The
+message itself is written at priority LOG@_CRIT.
+.endp
+Every log line starts with a timestamp, in the format shown in this example:
+.display asis
+2001-09-16 16:09:47 SMTP connection from [127.0.0.1] closed by QUIT
+.endd
+By default, the timestamps are in the local timezone. There are two
+ways of changing this:
+.numberpars $.
+You can set the \timezone\ option to a different time zone; in particular, if
+you set
+.display asis
+timezone = UTC
+.endd
+the timestamps will be in UTC (aka GMT).
+.nextp
+If you set \log@_timezone\ true, the time zone is added to the timestamp, for
+example:
+.display asis
+2003-04-25 11:17:07 +0100 Start queue run: pid=12762
+.endd
+.endp
+
+
+
+.section Where the logs are written
+.rset SECTwhelogwri "~~chapter.~~section"
+.index log||destination
+.index log||to file
+.index log||to syslog
+.index syslog
+The logs may be written to local files, or to syslog, or both. However, it
+should be noted that many syslog implementations use UDP as a transport, and
+are therefore unreliable in the sense that messages are not guaranteed to
+arrive at the loghost, nor is the ordering of messages necessarily maintained.
+It has also been reported that on large log files (tens of megabytes) you may
+need to tweak syslog to prevent it syncing the file with each write -- on Linux
+this has been seen to make syslog take 90% plus of CPU time.
+
+The destination for Exim's logs is configured by setting \\LOG@_FILE@_PATH\\ in
+\(Local/Makefile)\ or by setting \log@_file@_path\ in the run time
+configuration. This latter string is expanded, so it can contain, for example,
+references to the host name:
+.display asis
+log_file_path = /var/log/$primary_hostname/exim_%slog
+.endd
+It is generally advisable, however, to set the string in \(Local/Makefile)\
+rather than at run time, because then the setting is available right from the
+start of Exim's execution. Otherwise, if there's something it wants to log
+before it has read the configuration file (for example, an error in the
+configuration file) it will not use the path you want, and may not be able to
+log at all.
+
+The value of \\LOG@_FILE@_PATH\\ or \log@_file@_path\ is a colon-separated
+list, currently limited to at most two items. This is one option where the
+facility for changing a list separator may not be used. The list must always be
+colon-separated. If an item in the list is `syslog' then syslog is used;
+otherwise the item must either be an absolute path, containing \"%s"\ at the
+point where `main', `reject', or `panic' is to be inserted, or be empty,
+implying the use of a default path.
+
+When Exim encounters an empty item in the list, it searches the list defined by
+\\LOG@_FILE@_PATH\\, and uses the first item it finds that is neither empty nor
+`syslog'. This means that an empty item in \log@_file@_path\ can be used to
+mean `use the path specified at build time'. It no such item exists, log files
+are written in the \(log)\ subdirectory of the spool directory. This is
+equivalent to the setting:
+.display asis
+log_file_path = $spool_directory/log/%slog
+.endd
+If you do not specify anything at build time or run time, that is where the
+logs are written.
+
+A log file path may also contain \"%D"\ if datestamped log file names are in
+use -- see section ~~SECTdatlogfil below.
+
+Here are some examples of possible settings:
+.display
+.tabs 42
+LOG@_FILE@_PATH=syslog $t $rm{syslog only}
+LOG@_FILE@_PATH=:syslog $t $rm{syslog and default path}
+LOG@_FILE@_PATH=syslog : /usr/log/exim@_%s $t $rm{syslog and specified path}
+LOG@_FILE@_PATH=/usr/log/exim@_%s $t $rm{specified path only}
+.endd
+If there are more than two paths in the list, the first is used and a panic
+error is logged.
+
+
+.section Logging to local files that are periodically `cycled'
+.index log||cycling local files
+.index cycling logs
+.index \*exicyclog*\
+.index log||local files, writing to
+Some operating systems provide centralized and standardised methods for cycling
+log files. For those that do not, a utility script called \*exicyclog*\ is
+provided (see section ~~SECTcyclogfil). This renames and compresses the main
+and reject logs each time it is called. The maximum number of old logs to keep
+can be set. It is suggested this script is run as a daily \*cron*\ job.
+
+An Exim delivery process opens the main log when it first needs to write to it,
+and it keeps the file open in case subsequent entries are required -- for
+example, if a number of different deliveries are being done for the same
+message. However, remote SMTP deliveries can take a long time, and this means
+that the file may be kept open long after it is renamed if \*exicyclog*\ or
+something similar is being used to rename log files on a regular basis. To
+ensure that a switch of log files is noticed as soon as possible, Exim calls
+\*stat()*\ on the main log's name before reusing an open file, and if the file
+does not exist, or its inode has changed, the old file is closed and Exim
+tries to open the main log from scratch. Thus, an old log file may remain open
+for quite some time, but no Exim processes should write to it once it has been
+renamed.
+
+
+.section Datestamped log files
+.rset SECTdatlogfil "~~chapter.~~section"
+.index log||datestamped files
+Instead of cycling the main and reject log files by renaming them
+periodically, some sites like to use files whose names contain a datestamp,
+for example, \(mainlog-20031225)\. The datestamp is in the form \(yyyymmdd)\.
+Exim has support for this way of working. It is enabled by setting the
+\log@_file@_path\ option to a path that includes \"%D"\ at the point where the
+datestamp is required. For example:
+.display asis
+log_file_path = /var/spool/exim/log/%slog-%D
+log_file_path = /var/log/exim-%s-%D.log
+log_file_path = /var/spool/exim/log/%D-%slog
+.endd
+As before, \"%s"\ is replaced by `main' or `reject'; the following are examples
+of names generated by the above examples:
+.display asis
+/var/spool/exim/log/mainlog-20021225
+/var/log/exim-reject-20021225.log
+/var/spool/exim/log/20021225-mainlog
+.endd
+When this form of log file is specified, Exim automatically switches to new
+files at midnight. It does not make any attempt to compress old logs; you
+will need to write your own script if you require this. You should not
+run \*exicyclog*\ with this form of logging.
+
+The location of the panic log is also determined by \log@_file@_path\, but it
+is not datestamped, because rotation of the panic log does not make sense.
+When generating the name of the panic log, \"%D"\ is removed from the string.
+In addition, if it immediately follows a slash, a following non-alphanumeric
+character is removed; otherwise a preceding non-alphanumeric character is
+removed. Thus, the three examples above would give these panic log names:
+.display asis
+/var/spool/exim/log/paniclog
+/var/log/exim-panic.log
+/var/spool/exim/log/paniclog
+.endd
+
+
+.section Logging to syslog
+.index log||syslog, writing to
+The use of syslog does not change what Exim logs or the format of its messages,
+except in one respect. If \syslog@_timestamp\ is set false, the timestamps on
+Exim's log lines are omitted when these lines are sent to syslog. Apart from
+that, the same strings are written to syslog as to log files. The syslog
+`facility' is set to \\LOG@_MAIL\\, and the program name to `exim'
+by default, but you can change these by setting the \syslog@_facility\ and
+\syslog@_processname\ options, respectively. If Exim was compiled with
+\\SYSLOG@_LOG@_PID\\ set in \(Local/Makefile)\ (this is the default in
+\(src/EDITME)\), then, on systems that permit it (all except ULTRIX), the
+\\LOG@_PID\\ flag is set so that the \*syslog()*\ call adds the pid as well as
+the time and host name to each line.
+The three log streams are mapped onto syslog priorities as follows:
+.numberpars " "
+\*mainlog*\ is mapped to \\LOG@_INFO\\
+.nextp
+\*rejectlog*\ is mapped to \\LOG@_NOTICE\\
+.nextp
+\*paniclog*\ is mapped to \\LOG@_ALERT\\
+.endp
+Many log lines are written to both \*mainlog*\ and \*rejectlog*\, and some are
+written to both \*mainlog*\ and \*paniclog*\, so there will be duplicates if
+these are routed by syslog to the same place. You can suppress this duplication
+by setting \syslog@_duplication\ false.
+
+Exim's log lines can sometimes be very long, and some of its \*rejectlog*\
+entries contain multiple lines when headers are included. To cope with both
+these cases, entries written to syslog are split into separate \*syslog()*\
+calls at each internal newline, and also after a maximum of
+870 data characters. (This allows for a total syslog line length of 1024, when
+additions such as timestamps are added.) If you are running a syslog
+replacement that can handle lines longer than the 1024 characters allowed by
+RFC 3164, you should set
+.display asis
+SYSLOG_LONG_LINES=yes
+.endd
+in \(Local/Makefile)\ before building Exim. That stops Exim from splitting long
+lines, but it still splits at internal newlines in \*reject*\ log entries.
+
+To make it easy to re-assemble split lines later, each component of a split
+entry starts with a string of the form `[<<n>>/<<m>>]' or `[<<n>>@\<<m>>]'
+where <<n>> is the component number and <<m>> is the total number of components
+in the entry. The / delimiter is used when the line was split because it was
+too long; if it was split because of an internal newline, the @\ delimiter is
+used. For example, supposing the length limit to be 70 instead of 1000, the
+following would be the result of a typical rejection message to \*mainlog*\
+(LOG@_INFO), each line in addition being preceded by the time, host name, and
+pid as added by syslog:
+.display
+.indent 0
+$smc{[1/3] 2002-09-16 16:09:43 16RdAL-0006pc-00 rejected from [127.0.0.1] (ph10):
+[2/3] syntax error in 'From' header when scanning for sender: missing or ma
+[3/3] lformed local part in "<>" (envelope sender is <ph10@@cam.example>)}
+.endd
+The same error might cause the following lines to be written to `rejectlog'
+(LOG@_NOTICE):
+.display flow
+.indent 0
+$smc{[1/14] 2002-09-16 16:09:43 16RdAL-0006pc-00 rejected from [127.0.0.1] (ph10):
+[2/14] syntax error in 'From' header when scanning for sender: missing or ma
+[3@\14] lformed local part in "@<@>" (envelope sender is <ph10@@cam.example>)
+[4@\14] Recipients: ph10@@some.domain.cam.example
+[5@\14] P Received: from [127.0.0.1] (ident=ph10)
+[6@\14] by xxxxx.cam.example with smtp (Exim 4.00)
+[7@\14] id 16RdAL-0006pc-00
+[8@\14] for ph10@@cam.example; Mon, 16 Sep 2002 16:09:43 +0100
+[9@\14] F From: @<@>
+[10@\14] Subject: this is a test header
+[11@\14] X-something: this is another header
+[12@\14] I Message-Id: <E16RdAL-0006pc-00@@xxxxx.cam.example>
+[13@\14] B Bcc:
+[14/14] Date: Mon, 16 Sep 2002 16:09:43 +0100}
+.endd
+Log lines that are neither too long nor contain newlines are written to syslog
+without modification.
+
+If only syslog is being used, the Exim monitor is unable to provide a log tail
+display, unless syslog is routing \*mainlog*\ to a file on the local host and
+the environment variable \\EXIMON@_LOG@_FILE@_PATH\\ is set to tell the monitor
+where it is.
+
+
+.section Log line flags
+One line is written to the main log for each message received, and for each
+successful, unsuccessful, and delayed delivery. These lines can readily be
+picked out by the distinctive two-character flags that immediately follow the
+timestamp. The flags are:
+.display
+.tabs 6
+<= $t $rm{message arrival}
+=> $t $rm{normal message delivery}
+-> $t $rm{additional address in same delivery}
+*> $t $rm{delivery suppressed by \-N-\}
+** $t $rm{delivery failed; address bounced}
+== $t $rm{delivery deferred; temporary problem}
+.endd
+
+
+.section Logging message reception
+.index log||reception line
+The format of the single-line entry in the main log that is written for every
+message received is shown in the basic example below, which is split over
+several lines in order to fit it on the page:
+.display
+.indent 0
+2002-10-31 08:57:53 16ZCW1-0005MB-00 <= kryten@@dwarf.fict.example
+ H=mailer.fict.example [192.168.123.123] U=exim
+ P=smtp S=5678 id=<<incoming message id>>
+.endd
+The address immediately following `<=' is the envelope sender address. A bounce
+message is shown with the sender address `<>', and if it is locally generated,
+this is followed by an item of the form
+.display
+R=<<message id>>
+.endd
+which is a reference to the message that caused the bounce to be sent.
+
+.index \\HELO\\
+.index \\EHLO\\
+For messages from other hosts, the H and U fields identify the remote host and
+record the RFC 1413 identity of the user that sent the message, if one was
+received. The number given in square brackets is the IP address of the sending
+host. If there is a single, unparenthesized host name in the H field, as
+above, it has been verified to correspond to the IP address (see the
+\host@_lookup\ option). If the name is in parentheses, it was the name quoted
+by the remote host in the SMTP \\HELO\\ or \\EHLO\\ command, and has not been
+verified. If verification yields a different name to that given for \\HELO\\ or
+\\EHLO\\, the verified name appears first, followed by the \\HELO\\ or \\EHLO\\
+name in parentheses.
+
+Misconfigured hosts (and mail forgers) sometimes put an IP address, with or
+without brackets, in the \\HELO\\ or \\EHLO\\ command, leading to entries in
+the log containing text like these examples:
+.display
+H=(10.21.32.43) [192.168.8.34]
+H=([10.21.32.43]) [192.168.8.34]
+.endd
+This can be confusing. Only the final address in square brackets can be relied
+on.
+
+For locally generated messages (that is, messages not received over TCP/IP),
+the H field is omitted, and the U field contains the login name of the caller
+of Exim.
+
+.index authentication||logging
+.index \\AUTH\\||logging
+For all messages, the P field specifies the protocol used to receive the
+message. This is set to `asmtp' for messages received from hosts which have
+authenticated themselves using the SMTP \\AUTH\\ command. In this case there is
+an additional item A= followed by the name of the authenticator that was used.
+If an authenticated identification was set up by the authenticator's
+\server@_set@_id\ option, this is logged too, separated by a colon from the
+authenticator name.
+
+The id field records the existing message id, if present.
+.index size||of message
+The size of the received message is given by the S field. When the message is
+delivered, headers may get removed or added, so that the size of delivered
+copies of the message may not correspond with this value (and indeed may be
+different to each other).
+
+The \log@_selector\ option can be used to request the logging of additional
+data when a message is received. See section ~~SECTlogselector below.
+
+
+.section Logging deliveries
+.index log||delivery line
+The format of the single-line entry in the main log that is written for every
+delivery is shown in one of the examples below, for local and remote deliveries,
+respectively. Each example has been split into two lines in order to fit
+it on the page:
+.display
+.indent 0
+2002-10-31 08:59:13 16ZCW1-0005MB-00 => marv <marv@@hitch.fict.example>
+ R=localuser T=local@_delivery
+2002-10-31 09:00:10 16ZCW1-0005MB-00 => monk@@holistic.fict.example
+ R=dnslookup T=remote@_smtp H=holistic.fict.example [192.168.234.234]
+.endd
+For ordinary local deliveries, the original address is given in angle brackets
+after the final delivery address, which might be a pipe or a file. If
+intermediate address(es) exist between the original and the final address, the
+last of these is given in parentheses after the final address. The R and T
+fields record the router and transport that were used to process the address.
+
+If a shadow transport was run after a successful local delivery, the log line
+for the successful delivery has an item added on the end, of the form
+.display
+ST=<<shadow transport name>>
+.endd
+If the shadow transport did not succeed, the error message is put in
+parentheses afterwards.
+
+When more than one address is included in a single delivery (for example, two
+SMTP \\RCPT\\ commands in one transaction) the second and subsequent
+addresses are flagged with `$tt{@-@>}' instead of `$tt{@=@>}'. When two or more
+messages are delivered down a single SMTP connection, an asterisk follows the
+IP address in the log lines for the second and subsequent messages.
+
+The generation of a reply message by a filter file gets logged as a `delivery'
+to the addressee, preceded by `>'.
+
+The \log@_selector\ option can be used to request the logging of additional
+data when a message is delivered. See section ~~SECTlogselector below.
+
+
+.section Discarded deliveries
+.index discarded messages
+.index message||discarded
+.index delivery||discarded, logging
+When a message is discarded as a result of the command `seen finish' being
+obeyed in a filter file which generates no deliveries, a log entry of the form
+.display
+2002-12-10 00:50:49 16auJc-0001UB-00 => discarded
+ <low.club@@bridge.example> R=userforward
+.endd
+is written, to record why no deliveries are logged. When a message is discarded
+because it is aliased to `:blackhole:' the log line is like this:
+.display asis
+1999-03-02 09:44:33 10HmaX-0005vi-00 => :blackhole:
+ <hole@nowhere.example> R=blackhole_router
+.endd
+
+
+.section Deferred deliveries
+When a delivery is deferred, a line of the following form is logged:
+.display
+.indent 0
+2002-12-19 16:20:23 16aiQz-0002Q5-00 == marvin@@endrest.example
+ R=dnslookup T=smtp defer (146): Connection refused
+.endd
+In the case of remote deliveries, the error is the one that was given for the
+last IP address that was tried. Details of individual SMTP failures are also
+written to the log, so the above line would be preceded by something like
+.display
+.indent 0
+2002-12-19 16:20:23 16aiQz-0002Q5-00 Failed to connect to
+ mail1.endrest.example [192.168.239.239]: Connection refused
+.endd
+When a deferred address is skipped because its retry time has not been reached,
+a message is written to the log, but this can be suppressed by setting an
+appropriate value in \log@_selector\.
+
+
+.section Delivery failures
+.index delivery||failure, logging
+If a delivery fails because an address cannot be routed, a line of the
+following form is logged:
+.display asis
+.indent 0
+1995-12-19 16:20:23 0tRiQz-0002Q5-00 ** jim@trek99.example
+ <jim@trek99.example>: unknown mail domain
+.endd
+If a delivery fails at transport time, the router and transport are shown, and
+the response from the remote host is included, as in this example:
+.display asis
+.indent 0
+2002-07-11 07:14:17 17SXDU-000189-00 ** ace400@pb.example R=dnslookup
+.newline
+.em
+ T=remote_smtp: SMTP error from remote mailer after pipelined
+.newline
+.nem
+ RCPT TO:<ace400@pb.example>: host pbmail3.py.example
+ [192.168.63.111]: 553 5.3.0 <ace400@pb.example>...
+ Addressee unknown
+.endd
+.em
+The word `pipelined' indicates that the SMTP \\PIPELINING\\ extension was being
+used. See \hosts@_avoid@_esmtp\ in the \%smtp%\ transport for a way of
+disabling \\PIPELINING\\.
+.nem
+
+The log lines for all forms of delivery failure are flagged with \"**"\.
+
+
+.section Fake deliveries
+.index delivery||fake, logging
+If a delivery does not actually take place because the \-N-\ option has been
+used to suppress it, a normal delivery line is written to the log, except that
+`=>' is replaced by `$*$>'.
+
+
+.section Completion
+A line of the form
+.display
+2002-10-31 09:00:11 16ZCW1-0005MB-00 Completed
+.endd
+is written to the main log when a message is about to be removed from the spool
+at the end of its processing.
+
+
+
+.section Summary of Fields in Log Lines
+.index log||summary of fields
+A summary of the field identifiers that are used in log lines is shown in
+the following table:
+.display flow
+.tabs 8
+A $t $rm{authenticator name (and optional id)}
+C $t $rm{SMTP confirmation on delivery}
+.newline
+.em
+CV $t $rm{certificate verification status}
+DN $t $rm{distinguished name from peer certificate}
+DT $t $rm{time taken for a delivery}
+.newline
+.nem
+F $t $rm{sender address (on delivery lines)}
+H $t $rm{host name and IP address}
+.newline
+.em
+I $t $rm{local interface used}
+.newline
+.nem
+id $t $rm{message id for incoming message}
+P $t $rm{on \"<="\ lines: protocol used}
+.newline
+.em
+ $t $rm{on \"=>"\ lines: return path}
+QT $t $rm{time spent on queue}
+.newline
+.nem
+R $t $rm{on \"<="\ lines: reference for local bounce}
+ $t $rm{on \"=>"\ lines: router name}
+S $t $rm{size of message}
+ST $t $rm{shadow transport name}
+T $t $rm{on \"<="\ lines: message subject (topic)}
+ $t $rm{on \"=>"\ lines: transport name}
+U $t $rm{local user or RFC 1413 identity}
+X $t $rm{TLS cipher suite}
+.endd
+
+
+.section Other log entries
+Various other types of log entry are written from time to time. Most should be
+self-explanatory. Among the more common are:
+.numberpars $.
+.index retry||time not reached
+\*retry time not reached*\##An address previously suffered a temporary error
+during routing or local delivery, and the time to retry has not yet arrived.
+This message is not written to an individual message log file unless it happens
+during the first delivery attempt.
+.nextp
+\*retry time not reached for any host*\##An address previously suffered
+temporary errors during remote delivery, and the retry time has not yet arrived
+for any of the hosts to which it is routed.
+.nextp
+.index spool directory||file locked
+\*spool file locked*\##An attempt to deliver a message cannot proceed because
+some other Exim process is already working on the message. This can be quite
+common if queue running processes are started at frequent intervals. The
+\*exiwhat*\ utility script can be used to find out what Exim processes are
+doing.
+.nextp
+.em
+.index error||ignored
+\*error ignored*\##There are several circumstances that give rise to this
+message:
+.numberpars " "
+Exim failed to deliver a bounce message whose age was greater than
+\ignore__bounce__errors__after\. The bounce was discarded.
+.nextp
+A filter file set up a delivery using the `noerror' option, and the delivery
+failed. The delivery was discarded.
+.nextp
+A delivery set up by a router configured with
+.display asis
+errors_to = <>
+.endd
+failed. The delivery was discarded.
+.endp
+.nem
+.endp
+
+
+
+.section Reducing or increasing what is logged
+.rset SECTlogselector "~~chapter.~~section"
+.index log||selectors
+By setting the \log@_selector\ global option, you can disable some of Exim's
+default logging, or you can request additional logging. The value of
+\log@_selector\ is made up of names preceded by plus or minus characters. For
+example:
+.display asis
+log_selector = +arguments -retry_defer
+.endd
+The list of optional log items is in the following table, with the default
+selection marked by asterisks:
+.display flow
+.tabs 32
+ address@_rewrite $t $rm{address rewriting}
+ all@_parents $t $rm{all parents in => lines}
+ arguments $t $rm{command line arguments}
+*connection@_reject $t $rm{connection rejections}
+*delay@_delivery $t $rm{immediate delivery delayed (message queued)}
+.newline
+.em
+ deliver@_time $t $rm{time taken to perform delivery}
+.newline
+.nem
+ delivery@_size $t $rm{add S=nnn to => lines}
+*dnslist@_defer $t $rm{defers of DNS list (aka RBL) lookups}
+*etrn $t $rm{ETRN commands}
+*host@_lookup@_failed $t $rm{as it says}
+.newline
+.em
+ ident@_timeout $t $rm{timeout for ident connection}
+.newline
+.nem
+ incoming@_interface $t $rm{incoming interface on <= lines}
+ incoming@_port $t $rm{incoming port on <= lines}
+*lost@_incoming@_connection $t $rm{as it says (includes timeouts)}
+.newline
+.em
+ outgoing@_port $t $rm{add remote port to => lines}
+.newline
+.nem
+*queue@_run $t $rm{start and end queue runs}
+.newline
+.em
+ queue@_time $t $rm{time on queue}
+.newline
+.nem
+ received@_recipients $t $rm{recipients on <= lines}
+ received@_sender $t $rm{sender on <= lines}
+*rejected@_header $t $rm{header contents on reject log}
+*retry@_defer $t $rm{`retry time not reached'}
+.newline
+.em
+ return@_path@_on@_delivery $t $rm{put return path on => and ** lines}
+.newline
+.nem
+ sender@_on@_delivery $t $rm{add sender to => lines}
+*size@_reject $t $rm{rejection because too big}
+*skip@_delivery $t $rm{`message is frozen', `spool file is locked'}
+.newline
+.em
+ smtp@_confirmation $t $rm{SMTP confirmation on => lines}
+.newline
+.nem
+ smtp@_connection $t $rm{SMTP connections}
+ smtp@_incomplete@_transaction $t $rm{incomplete SMTP transactions}
+ smtp@_protocol@_error $t $rm{SMTP protocol errors}
+ smtp@_syntax@_error $t $rm{SMTP syntax errors}
+ subject $t $rm{contents of ::Subject:: on <= lines}
+.newline
+.em
+ tls@_certificate@_verified $t $rm{certificate verification status}
+.newline
+.nem
+*tls@_cipher $t $rm{TLS cipher suite on <= and => lines}
+ tls@_peerdn $t $rm{TLS peer DN on <= and => lines}
+
+ all $t $rm{all of the above}
+.endd
+More details on each of these items follows:
+.numberpars $.
+.index log||rewriting
+.index rewriting||logging
+\address@_rewrite\: This applies both to global rewrites and per-transport
+rewrites,
+.em
+but not to rewrites in filters run as an unprivileged user (because such users
+cannot access the log).
+.nem
+.nextp
+.index log||full parentage
+\all@_parents\: Normally only the original and final addresses are logged on
+delivery lines; with this selector, intermediate parents are given in
+parentheses between them.
+.nextp
+.index log||Exim arguments
+.index Exim arguments, logging
+\arguments\: This causes Exim to write the arguments with which it was called
+to the main log,
+preceded by the current working directory.
+This is a debugging feature, added to make it easier to find out how certain
+MUAs call \(/usr/sbin/sendmail)\. The logging does not happen if Exim has given
+up root privilege because it was called with the \-C-\ or \-D-\ options.
+Arguments that are empty or that contain whitespace are quoted. Non-printing
+characters are shown as escape sequences.
+This facility cannot log unrecognized arguments, because the arguments are
+checked before the configuration file is read. The only way to log such cases
+is to interpose a script such as \(util/logargs.sh)\ between the caller and
+Exim.
+.nextp
+.index log||connection rejections
+\connection@_reject\: A log entry is written whenever an incoming SMTP
+connection is rejected, for whatever reason.
+.nextp
+.index log||delayed delivery
+.index delayed delivery, logging
+\delay@_delivery\: A log entry is written whenever a delivery process is not
+started for an incoming message because the load is too high or too many
+messages were received on one connection. Logging does not occur if no delivery
+process is started because \queue@_only\ is set or \-odq-\ was used.
+.nextp
+.em
+.index log||delivery duration
+\deliver@_time\: For each delivery, the amount of real time it has taken to
+perform the actual delivery is logged as DT=<<time>>, for example, \"DT=1s"\.
+.nem
+.nextp
+.index log||message size on delivery
+.index size||of message
+\delivery@_size\: For each delivery, the size of message delivered is added to
+the `=>' line, tagged with S=.
+.nextp
+.index log||dnslist defer
+.index DNS list||logging defer
+.index black list (DNS)
+\dnslist@_defer\: A log entry is written if an attempt to look up a host in a
+DNS black list suffers a temporary error.
+.nextp
+.index log||ETRN commands
+.index \\ETRN\\||logging
+\etrn\: Every legal ETRN command that is received is logged, before the ACL is
+run to determine whether or not it is actually accepted. An invalid ETRN
+command, or one received within a message transaction is not logged by this
+selector (see \smtp@_syntax@_error\ and \smtp@_protocol@_error\).
+.nextp
+.index log||host lookup failure
+\host@_lookup@_failed\: When a lookup of a host's IP addresses fails to find
+any addresses, or when a lookup of an IP address fails to find a host name, a
+log line is written. This logging does not apply to direct DNS lookups when
+routing email addresses, but it does apply to `byname' lookups.
+.nextp
+.em
+.index log||ident timeout
+.index RFC 1413||logging timeout
+\ident@_timeout\: A log line is written whenever an attempt to connect to a
+client's ident port times out.
+.nem
+.nextp
+.index log||incoming interface
+.index interface||logging
+\incoming@_interface\: The interface on which a message was received is added
+to the `<=' line as an IP address in square brackets, tagged by I= and followed
+by a colon and the port number.
+.em
+The local interface and port are also added to other SMTP log
+lines, for example `SMTP connection from', and to rejection lines.
+.nem
+.nextp
+.index log||incoming remote port
+.index port||logging remote
+.index TCP/IP||logging incoming remote port
+\incoming@_port\: The remote port number from which a message was received is
+added to log entries and ::Received:: header lines, following the IP address in
+square brackets, and separated from it by a colon. This is implemented by
+changing the value that is put in the \$sender@_fullhost$\ and
+\$sender@_rcvhost$\ variables. Recording the remote port number has become more
+important with the widening use of NAT (see RFC 2505).
+.nextp
+.index log||dropped connection
+\lost@_incoming@_connection\: A log line is written when an incoming SMTP
+connection is unexpectedly dropped.
+.nextp
+.em
+.index log||outgoing remote port
+.index port||logging outgoint remote
+.index TCP/IP||logging ougtoing remote port
+\outgoing@_port\: The remote port number is added to delivery log lines (those
+containing => tags) following the IP address. This option is not included in
+the default setting, because for most ordinary configurations, the remote port
+number is always 25 (the SMTP port).
+.nem
+.nextp
+.index log||queue run
+.index queue runner||logging
+\queue@_run\: The start and end of every queue run are logged.
+.nextp
+.em
+.index log||queue time
+\queue@_time\: The amount of time the message has been in the queue on the
+local host is logged as QT=<<time>>, for example, \"QT=3m45s"\. The clock
+starts when Exim starts to receive the message, so it includes reception time
+as well as the delivery time of the current address.
+.nem
+.nextp
+.index log||recipients
+\received@_recipients\: The recipients of a message are listed in the main log
+as soon as the message is received. The list appears at the end of the log line
+that is written when a message is received, preceded by the word `for'. The
+addresses are listed after they have been qualified, but before any rewriting
+has taken place.
+Recipients that were discarded by an ACL for \\MAIL\\ or \\RCPT\\ do not appear
+in the list.
+.nextp
+.index log||sender reception
+\received@_sender\: The unrewritten original sender of a message is added to
+the end of the log line that records the message's arrival, after the word
+`from' (before the recipients if \received@_recipients\ is also set).
+.nextp
+.index log||header lines for rejection
+\rejected@_header\: If a message's header has been received at the time a
+rejection is written to the reject log, the complete header is added to the
+log. Header logging can be turned off individually for messages that are
+rejected by the \*local@_scan()*\ function (see section ~~SECTapiforloc).
+.nextp
+.index log||retry defer
+\retry@_defer\: A log line is written if a delivery is deferred because a retry
+time has not yet been reached. However, this `retry time not reached' message
+is always omitted from individual message logs after the first delivery
+attempt.
+.nextp
+.index log||return path
+.em
+\return@_path@_on@_delivery\: The return path that is being transmitted with
+the message is included in delivery and bounce lines, using the tag P=.
+.nem
+.nextp
+.index log||sender on delivery
+\sender@_on@_delivery\: The message's sender address is added to every delivery
+and bounce line, tagged by F= (for `from').
+.em
+This is the original sender that was received with the message; it is not
+necessarily the same as the outgoing return path.
+.nem
+.nextp
+.index log||size rejection
+\size@_reject\: A log line is written whenever a message is rejected because it
+is too big.
+.nextp
+.index log||frozen messages, skipped
+.index frozen messages||logging skipping
+\skip@_delivery\: A log line is written whenever a message is skipped during a
+queue run because it is frozen or because another process is already delivering
+it.
+.nextp
+.index log||smtp confirmation
+.index SMTP||logging confirmation
+\smtp@_confirmation\: The response to the final `.' in the SMTP dialogue for
+outgoing messages is added to delivery log lines in the form `C="<<text>>"'. A
+number of MTAs (including Exim) return an identifying string in this response.
+.nextp
+.index log||SMTP connections
+.index SMTP||logging connections
+\smtp@_connection\: A log line is written whenever an SMTP connection is
+established or closed. (By contrast, \lost@_incoming@_connection\ applies only
+when the closure is unexpected.) This applies to connections from local
+processes that use \-bs-\ as well as to TCP/IP connections. If a connection is
+dropped in the middle of a message, a log line is always written, whether this
+selector is set or not, but otherwise nothing is written at the start and end
+of connections unless this selector is enabled.
+
+For TCP/IP connections to an Exim daemon, the current number of connections is
+included in the log message for each new connection, but note that the count is
+reset if the daemon is restarted.
+Also, because connections are closed (and the closure is logged) in
+subprocesses, the count may not include connections that have been closed but
+whose termination the daemon has not yet noticed. Thus, while it is possible to
+match up the opening and closing of connections in the log, the value of the
+logged counts may not be entirely accurate.
+.nextp
+.index log||SMTP transaction, incomplete
+.index SMTP||logging incomplete transactions
+\smtp@_incomplete@_transaction\: When a mail transaction is aborted by
+\\RSET\\, \\QUIT\\, loss of connection, or otherwise, the incident is logged,
+and the message sender plus any accepted recipients are included in the log
+line. This can provide evidence of dictionary attacks.
+.nextp
+.index log||SMTP protocol error
+.index SMTP||logging protocol error
+\smtp@_protocol@_error\: A log line is written for every SMTP protocol error
+encountered.
+.em
+Exim does not have perfect detection of all protocol errors because of
+transmission delays and the use of pipelining. If \\PIPELINING\\ has been
+advertised to a client, an Exim server assumes that the client will use it, and
+therefore it does not count `expected' errors (for example, \\RCPT\\ received
+after rejecting \\MAIL\\) as protocol errors.
+.nem
+.nextp
+.index SMTP||logging syntax errors
+.index SMTP||syntax errors, logging
+.index SMTP||unknown command, logging
+.index log||unknown SMTP command
+.index log||SMTP syntax error
+\smtp@_syntax@_error\: A log line is written for every SMTP syntax error
+encountered. An unrecognized command is treated as a syntax error. For an
+external connection, the host identity is given; for an internal connection
+using \-bs-\ the sender identification (normally the calling user) is given.
+.nextp
+.index log||subject
+.index subject, logging
+\subject\: The subject of the message is added to the arrival log line,
+preceded by `T=' (T for `topic', since S is already used for `size').
+Any MIME `words' in the subject are decoded. The \print@_topbitchars\ option
+specifies whether characters with values greater than 127 should be logged
+unchanged, or whether they should be rendered as escape sequences.
+.nextp
+.index log||certificate verification
+.em
+\tls@_certificate@_verified\: An extra item is added to <= and => log lines
+when TLS is in use. The item is \"CV=yes"\ if the peer's certificate was
+verified, and \"CV=no"\ if not.
+.nem
+.nextp
+.index log||TLS cipher
+.index TLS||logging cipher
+\tls@_cipher\: When a message is sent or received over an encrypted connection,
+the cipher suite used is added to the log line, preceded by X=.
+.nextp
+.index log||TLS peer DN
+.index TLS||logging peer DN
+\tls@_peerdn\: When a message is sent or received over an encrypted connection,
+and a certificate is supplied by the remote host, the peer DN is added to the
+log line, preceded by DN=.
+.endp
+
+.section Message log
+.index message||log file for
+.index log||message log, description of
+In addition to the general log files, Exim writes a log file for each message
+that it handles. The names of these per-message logs are the message ids, and
+.index \(msglog)\ directory
+they are kept in the \(msglog)\ sub-directory of the spool directory. Each
+message log contains copies of the log lines that apply to the message. This
+makes it easier to inspect the status of an individual message without having
+to search the main log. A message log is deleted when processing of the message
+is complete,
+.index \preserve@_message@_logs\
+unless \preserve__message__logs\ is set, but this should be used only with
+great care because they can fill up your disk very quickly.
+
+On a heavily loaded system, it may be desirable to disable the use of
+per-message logs, in order to reduce disk I/O. This can be done by setting the
+\message@_logs\ option false.
+
+
+
+.
+.
+.
+. ============================================================================
+.chapter Exim utilities
+.set runningfoot "utilities"
+.rset CHAPutils ~~chapter
+.index utilities
+A number of utility scripts and programs are supplied with Exim and are
+described in this chapter. There is also the Exim Monitor, which is covered in
+the next chapter. The utilities described here are:
+
+. This duplication seems to be the only way to arrange that the cross-
+. references are omitted in the Texinfo version. They look horribly ugly.
+
+.if ~~texinfo
+.display rm
+.tabs 22
+\*exiwhat*\ $t $rm{list what Exim processes are doing}
+.newline
+\*exiqgrep*\ $t $rm{grep the queue}
+.newline
+\*exiqsumm*\ $t $rm{summarize the queue}
+\*exigrep*\ $t $rm{search the main log}
+\*exipick*\ $t $rm{select messages on various criteria}
+\*exicyclog*\ $t $rm{cycle (rotate) log files}
+\*eximstats*\ $t $rm{extract statistics from the log}
+\*exim@_checkaccess*\ $t $rm{check address acceptance from given IP}
+\*exim@_dbmbuild*\ $t $rm{build a DBM file}
+\*exinext*\ $t $rm{extract retry information}
+\*exim@_dumpdb*\ $t $rm{dump a hints database}
+\*exim@_tidydb*\ $t $rm{clean up a hints database}
+\*exim@_fixdb*\ $t $rm{patch a hints database}
+\*exim@_lock*\ $t $rm{lock a mailbox file}
+.endd
+.
+.else
+.
+.display rm
+.tabs 22
+~~SECTfinoutwha \*exiwhat*\ $t $rm{list what Exim processes are doing}
+.newline
+~~SECTgreptheque \*exiqgrep*\ $t $rm{grep the queue}
+.newline
+~~SECTsumtheque \*exiqsumm*\ $t $rm{summarize the queue}
+~~SECTextspeinf \*exigrep*\ $t $rm{search the main log}
+.newline
+.em
+~~SECTexipick \*exipick*\ $t $rm{select messages on various criteria}
+.newline
+.nem
+~~SECTcyclogfil \*exicyclog*\ $t $rm{cycle (rotate) log files}
+~~SECTmailstat \*eximstats*\ $t $rm{extract statistics from the log}
+~~SECTcheckaccess \*exim@_checkaccess*\ $t $rm{check address acceptance from given IP}
+~~SECTdbmbuild \*exim@_dbmbuild*\ $t $rm{build a DBM file}
+~~SECTfinindret \*exinext*\ $t $rm{extract retry information}
+~~SECThindatmai \*exim@_dumpdb*\ $t $rm{dump a hints database}
+~~SECThindatmai \*exim@_tidydb*\ $t $rm{clean up a hints database}
+~~SECThindatmai \*exim@_fixdb*\ $t $rm{patch a hints database}
+~~SECTmailboxmaint \*exim@_lock*\ $t $rm{lock a mailbox file}
+.endd
+.fi
+
+.section Finding out what Exim processes are doing (exiwhat)
+.rset SECTfinoutwha "~~chapter.~~section"
+.index \*exiwhat*\
+.index process, querying
+.index \\SIGUSR1\\
+On operating systems that can restart a system call after receiving a signal
+(most modern OS), an Exim process responds to the \\SIGUSR1\\ signal by writing
+a line describing what it is doing to the file \(exim-process.info)\ in the
+Exim spool directory. The \*exiwhat*\ script sends the signal to all Exim
+processes it can find, having first emptied the file. It then waits for one
+second to allow the Exim processes to react before displaying the results.
+In order to run \*exiwhat*\ successfully you have to have sufficient privilege to
+send the signal to the Exim processes, so it is normally run as root.
+
+Unfortunately, the \*ps*\ command which \*exiwhat*\ uses to find Exim processes
+varies in different operating systems. Not only are different options used,
+but the format of the output is different. For this reason, there are some
+system configuration options that configure exactly how \*exiwhat*\ works. If it
+doesn't seem to be working for you, check the following compile-time options:
+.display
+EXIWHAT@_PS@_CMD $rm{the command for running \*ps*\}
+EXIWHAT@_PS@_ARG $rm{the argument for \*ps*\}
+EXIWHAT@_EGREP@_ARG $rm{the argument for \*egrep*\ to select from \*ps*\ output}
+EXIWHAT@_KILL@_ARG $rm{the argument for the \*kill*\ command}
+.endd
+An example of typical output from \*exiwhat*\ is
+.display
+.indent 0
+ 164 daemon: -q1h, listening on port 25
+10483 running queue: waiting for 0tAycK-0002ij-00 (10492)
+10492 delivering 0tAycK-0002ij-00 to mail.ref.example [10.19.42.42]
+ (editor@@ref.example)
+10592 handling incoming call from [192.168.243.242]
+10628 accepting a local non-SMTP message
+.endd
+The first number in the output line is the process number. The third line has
+been split here, in order to fit it on the page.
+
+
+.section Selective queue listing (exiqgrep)
+.rset SECTgreptheque "~~chapter.~~section"
+.index \*exiqgrep*\
+.index queue||grepping
+This utility is a Perl script contributed by Matt Hubbard. It runs
+.display asis
+exim -bpu
+.endd
+to obtain a queue listing with undelivered recipients only, and then greps the
+output to select messages that match given criteria. The following selection
+options are available:
+
+.startoptions
+
+.option f <<regex>>
+Match the sender address. The field that is tested is enclosed in angle
+brackets, so you can test for bounce messages with
+.display asis
+exiqgrep -f '^<>$'
+.endd
+
+.option r <<regex>>
+Match a recipient address. The field that is tested is not enclosed in angle
+brackets.
+
+.option s <<regex>>
+Match against the size field.
+
+.option y <<seconds>>
+Match messages that are younger than the given time.
+
+.option o <<seconds>>
+Match messages that are older than the given time.
+
+.option z
+Match only frozen messages.
+
+.option x
+Match only non-frozen messages.
+
+.endoptions
+
+The following options control the format of the output:
+
+.startoptions
+
+.option c
+Display only the count of matching messages.
+
+.option l
+Long format -- display the full message information as output by Exim. This is
+the default.
+
+.option i
+Display message ids only.
+
+.option b
+Brief format -- one line per message.
+
+.option R
+Display messages in reverse order.
+
+.endoptions
+
+There is one more option, \-h-\, which outputs a list of options.
+
+
+.section Summarising the queue (exiqsumm)
+.rset SECTsumtheque "~~chapter.~~section"
+.index \*exiqsumm*\
+.index queue||summary
+The \*exiqsumm*\ utility is a Perl script which reads the output of \*exim
+-bp*\ and produces a summary of the messages on the queue. Thus, you use it by
+running a command such as
+.display asis
+exim -bp | exiqsumm
+.endd
+The output consists of one line for each domain that has messages waiting for
+it, as in the following example:
+.display asis
+ 3 2322 74m 66m msn.com.example
+.endd
+Each line lists the number of
+pending deliveries for a domain, their total volume, and the length of time
+that the oldest and the newest messages have been waiting. Note that the number
+of pending deliveries is greater than the number of messages when messages
+have more than one recipient.
+
+A summary line is output at the end. By default the output is sorted on the
+domain name, but \*exiqsumm*\ has the options \-a-\ and \-c-\, which cause the
+output to be sorted by oldest message and by count of messages, respectively.
+
+The output of \*exim -bp*\ contains the original addresses in the message, so
+this also applies to the output from \*exiqsumm*\. No domains from addresses
+generated by aliasing or forwarding are included (unless the \one@_time\ option
+of the \%redirect%\ router has been used to convert them into `top level'
+addresses).
+
+
+
+.section Extracting specific information from the log (exigrep)
+.rset SECTextspeinf "~~chapter.~~section"
+.index \*exigrep*\
+.index log||extracts, grepping for
+The \*exigrep*\ utility is a Perl script that searches one or more main log
+files for entries that match a given pattern. When it finds a match, it
+extracts all the log entries for the relevant message, not just those that
+match the pattern. Thus, \*exigrep*\ can extract complete log entries for a
+given message, or all mail for a given user, or for a given host, for example.
+
+.em
+If a matching log line is not associated with a specific message, it is always
+included in \*exigrep*\'s output.
+.nem
+The usage is:
+.display asis
+exigrep [-l] [-t<n>] <pattern> [<log file>] ...
+.endd
+The \-t-\ argument specifies a number of seconds. It adds an additional
+condition for message selection. Messages that are complete are shown only if
+they spent more than <<n>> seconds on the queue.
+
+The \-l-\ flag means `literal', that is, treat all characters in the
+pattern as standing for themselves. Otherwise the pattern must be a Perl
+regular expression. The pattern match is case-insensitive. If no file names are
+given on the command line, the standard input is read.
+
+If the location of a \*zcat*\ command is known from the definition of
+\\ZCAT@_COMMAND\\ in \(Local/Makefile)\, \*exigrep*\ automatically passes any
+file whose name ends in \\COMPRESS@_SUFFIX\\ through \*zcat*\ as it searches
+it.
+
+.em
+.section Selecting messages by various criteria (exipick)
+.rset SECTexipick "~~chapter.~~section"
+.index \*exipick*\
+John Jetmore's \*exipick*\ utility is included in the Exim distribution. It
+lists messages from the queue according to a variety of criteria. For details,
+run:
+.display asis
+exipick --help
+.endd
+.nem
+
+
+.section Cycling log files (exicyclog)
+.rset SECTcyclogfil "~~chapter.~~section"
+.index log||cycling local files
+.index cycling logs
+.index \*exicyclog*\
+The \*exicyclog*\ script can be used to cycle (rotate) \*mainlog*\ and
+\*rejectlog*\ files. This is not necessary if only syslog is being used,
+or if you are using log files with datestamps in their names (see section
+~~SECTdatlogfil).
+Some operating systems have their own standard mechanisms for log cycling, and
+these can be used instead of \*exicyclog*\ if preferred.
+
+Each time \*exicyclog*\ is run the file names get `shuffled down' by one. If the
+main log file name is \(mainlog)\ (the default) then when \*exicyclog*\ is run
+\(mainlog)\ becomes \(mainlog.01)\, the previous \(mainlog.01)\ becomes
+\(mainlog.02)\ and so on, up to a limit which is set in the script, and which
+defaults to 10. Reject logs are handled similarly.
+
+If no \(mainlog)\ file exists, the script does nothing. Files that `drop off'
+the end are deleted. All files with numbers greater than 01 are compressed,
+using a compression command which is configured by the \\COMPRESS@_COMMAND\\
+setting in \(Local/Makefile)\. It is usual to run \*exicyclog*\ daily from a
+root \crontab\ entry of the form
+.display
+1 0 * * * su exim -c /usr/exim/bin/exicyclog
+.endd
+assuming you have used the name `exim' for the Exim user. You can run
+\*exicyclog*\ as root if you wish, but there is no need.
+
+
+.section Mail statistics (eximstats)
+.rset SECTmailstat "~~chapter.~~section"
+.index statistics
+.index \*eximstats*\
+A Perl script called \*eximstats*\ is provided for extracting statistical
+information from log files. The output is either plain text, or HTML.
+Exim log files are also suported by the \*Lire*\ system produced by the
+LogReport Foundation (\?http://www.logreport.org?\).
+
+The \*eximstats*\ script has been hacked about quite a bit over time. The
+latest version is the result of some extensive revision by Steve Campbell. A
+lot of information is given by default, but there are options for suppressing
+various parts of it. Following any options, the arguments to the script are a
+list of files, which should be main log files. For example:
+.display asis
+eximstats -nr /var/spool/exim/log/mainlog.01
+.endd
+By default, \*eximstats*\ extracts information about the number and volume of
+messages received from or delivered to various hosts. The information is sorted
+both by message count and by volume, and the top fifty hosts in each category
+are listed on the standard output. Similar information, based on email
+addresses or domains instead of hosts can be requested by means of various
+options. For messages delivered and received locally, similar statistics are
+also produced per user.
+
+The output also includes total counts and statistics about delivery errors, and
+histograms showing the number of messages received and deliveries made in each
+hour of the day. A delivery with more than one address in its envelope (for
+example, an SMTP transaction with more than one \\RCPT\\ command) is counted
+as a single delivery by \*eximstats*\.
+
+Though normally more deliveries than receipts are reported (as messages may
+have multiple recipients), it is possible for \*eximstats*\ to report more
+messages received than delivered, even though the queue is empty at the start
+and end of the period in question. If an incoming message contains no valid
+recipients, no deliveries are recorded for it. A bounce message is handled as
+an entirely separate message.
+
+\*eximstats*\ always outputs a grand total summary giving the volume and number
+of messages received and deliveries made, and the number of hosts involved in
+each case. It also outputs the number of messages that were delayed (that is,
+not completely delivered at the first attempt), and the number that had at
+least one address that failed.
+
+The remainder of the output is in sections that can be independently disabled
+or modified by various options. It consists of a summary of deliveries by
+transport, histograms of messages received and delivered per time interval
+(default per hour), information about the time messages spent on the queue,
+a list of relayed messages, lists of the top fifty sending hosts, local
+senders, destination hosts, and destination local users by count and by volume,
+and a list of delivery errors that occurred.
+
+The relay information lists messages that were actually relayed, that is, they
+came from a remote host and were directly delivered to some other remote host,
+without being processed (for example, for aliasing or forwarding) locally.
+
+The options for \*eximstats*\ are as follows:
+
+.startoptions
+.index \*eximstats*\||options
+.option bydomain
+The `league tables' are computed on the basis of the superior domains of the
+sending hosts instead of the sending and receiving hosts. This option may be
+combined with \-byhost-\ and/or \-byemail-\.
+
+.option byedomain
+This is a synonym for \-byemaildomain-\.
+
+.option byemail
+The `league tables' are computed on the basis of complete email addresses,
+instead of sending and receiving hosts. This option may be combined with
+\-byhost-\ and/or \-bydomain-\.
+
+.option byemaildomain
+The `league tables' are computed on the basis of the sender's email domain
+instead of the sending and receiving hosts. This option may be combined with
+\-byhost-\, \-bydomain-\, or \-byemail-\.
+
+.option byhost
+The `league tables' are computed on the basis of sending and receiving hosts.
+This is the default option. It may be combined with \-bydomain-\ and/or
+\-byemail-\.
+
+.option cache
+Cache results of \*timegm()*\ lookups. This results in a significant speedup
+when processing hundreds of thousands of messages, at a cost of increasing the
+memory utilisation.
+
+.option chartdir <<dir>>
+When \-charts-\ is specified, create the charts in the directory <<dir>>.
+
+.option chartrel <<dir>>
+When \-charts-\ is specified, this option specifies the relative directory for
+the \"img src="\ tags from where to include the charts.
+
+.option charts
+Create graphical charts to be displayed in HTML output. This requires the
+\"GD"\, \"GDTextUtil"\, and \"GDGraph"\ Perl modules, which can be obtained
+from \?http://www.cpan.org/modules/01modules.index.html?\.
+
+To install these, download and unpack them, then use the normal Perl
+installation procedure:
+.display asis
+perl Makefile.PL
+make
+make test
+make install
+.endd
+
+.option d
+This is a debug flag. It causes \*eximstats*\ to output the \*eval()*\'d parser
+to the standard output, which makes it easier to trap errors in the eval
+section. Remember to add one to the line numbers to allow for the title.
+
+
+.option help
+Show help information about \*eximstats*\' options.
+
+.option h <<n>>
+This option controls the histograms of messages received and deliveries per
+time interval. By default the time interval is one hour. If \-h0-\ is given,
+the histograms are suppressed; otherwise the value of <<n>> gives the number of
+divisions per hour. Valid values are 0, 1, 2, 3, 5, 10, 15, 20, 30 or 60, so
+\-h2-\ sets an interval of 30 minutes, and the default is equivalent to \-h1-\.
+
+.option html
+Output the results in HTML instead of plain text.
+
+.option merge
+This option causes \*eximstats*\ to merge old reports into a combined report.
+When this option is used, the input files must be outputs from previous calls
+to \*eximstats*\, not raw log files. For example, you could produce a set of
+daily reports and a weekly report by commands such as
+.display asis
+eximstats mainlog.sun > report.sun.txt
+eximstats mainlog.mon > report.mon.txt
+eximstats mainlog.tue > report.tue.txt
+eximstats mainlog.wed > report.wed.txt
+eximstats mainlog.thu > report.thu.txt
+eximstats mainlog.fri > report.fri.txt
+eximstats mainlog.sat > report.sat.txt
+eximstats -merge -html report.*.txt > weekly_report.html
+.endd
+You can merge text or html reports and output the results as text or html. You
+can use all the normal \*eximstats*\ output options, but only data included in
+the original reports can be shown. When merging reports, some loss of accuracy
+may occur in the `league tables', towards the ends of the lists. The order of
+items in the `league tables' may vary when the data volumes round to the same
+value.
+
+.option ne
+Suppress the display of information about failed deliveries (errors).
+
+.option nr
+Suppress information about messages relayed through this host.
+
+.option nr /pattern/
+Suppress information about relayed messages that match the pattern, which is
+matched against a string of the following form (split over two lines here in
+order to fit it on the page):
+.display asis
+H=<host> [<ip address>] A=<sender address> =>
+ H=<host> A=<recipient address>
+.endd
+for example
+.display asis
+H=in.host [1.2.3.4] A=from@some.where.example =>
+ H=out.host A=to@else.where.example
+.endd
+The sending host name appears in parentheses if it has not been verified as
+matching the IP address. The mail addresses are taken from the envelope, not
+the headers. This option allows you to screen out hosts whom you are happy to
+have using your host as a relay.
+
+.option nt
+Suppress the statistics about delivery by transport.
+
+.option nt/<<pattern>>/
+Suppress the statistics about delivery by any transport whose name matches the
+pattern. If you are using one transport to send all messages to a scanning
+mechanism before doing the real delivery, this feature can be used to omit that
+transport from your normal statistics (on the grounds that it is of no
+interest).
+
+
+.option "pattern" "#<<description>>#/<<pattern>>/"
+Count lines matching specified patterns and show them in
+the results. For example:
+.display asis
+-pattern 'Refused connections' '/refused connection/'
+.endd
+This option can be specified multiple times.
+
+.option q0
+Suppress information about times messages spend on the queue.
+
+.option q <<n1>>...
+This option sets an alternative list of time intervals for the queueing
+information. The values are separated by commas and are in seconds, but can
+involve arithmetic multipliers, so for example you can set 3$*$60 to specify 3
+minutes. A setting such as
+.display asis
+-q60,5*60,10*60
+.endd
+causes \*eximstats*\ to give counts of messages that stayed on the queue for less
+than one minute, less than five minutes, less than ten minutes, and over ten
+minutes.
+
+.option t <<n>>
+Sets the `top' count to <<n>>. This controls the listings of the `top <<n>>'
+hosts and users by count and volume. The default is 50, and setting 0
+suppresses the output altogether.
+
+.option tnl
+Omit local information from the `top' listings.
+
+.option t@_remote@_users
+Include remote users in the `top' listings.
+
+.endoptions
+
+
+.section Checking access policy (exim@_checkaccess)
+.rset SECTcheckaccess "~~chapter.~~section"
+.index \*exim@_checkaccess*\
+.index policy control||checking access
+.index checking access
+The \-bh-\ command line argument allows you to run a fake SMTP session with
+debugging output, in order to check what Exim is doing when it is applying
+policy controls to incoming SMTP mail. However, not everybody is sufficiently
+familiar with the SMTP protocol to be able to make full use of \-bh-\, and
+sometimes you just want to answer the question \*Does this address have
+access?*\ without bothering with any further details.
+
+The \*exim@_checkaccess*\ utility is a `packaged' version of \-bh-\. It takes
+two arguments, an IP address and an email address:
+.display asis
+exim_checkaccess 10.9.8.7 A.User@a.domain.example
+.endd
+The utility runs a call to Exim with the \-bh-\ option, to test whether the
+given email address would be accepted in a \\RCPT\\ command in a TCP/IP
+connection from the host with the given IP address. The output of the utility
+is either the word `accepted', or the SMTP error response, for example:
+.display asis
+Rejected:
+ 550 Relay not permitted
+.endd
+When running this test, the utility uses \"<>"\ as the envelope sender address
+for the \\MAIL\\ command, but you can change this by providing additional
+options. These are passed directly to the Exim command. For example, to specify
+that the test is to be run with the sender address \*himself@@there.example*\
+you can use:
+.display asis
+exim_checkaccess 10.9.8.7 A.User@a.domain.example \
+ -f himself@there.example
+.endd
+Note that these additional Exim command line items must be given after the two
+mandatory arguments.
+
+Because the \exim@_checkaccess\ uses \-bh-\, it does not perform callouts while
+running its checks. You can run checks that include callouts by using \-bhc-\,
+but this is not yet available in a `packaged' form.
+
+
+.section Making DBM files (exim@_dbmbuild)
+.rset SECTdbmbuild "~~chapter.~~section"
+.index DBM||building dbm files
+.index building DBM files
+.index \*exim@_dbmbuild*\
+.index lower casing
+.index binary zero||in lookup key
+The \*exim@_dbmbuild*\ program reads an input file containing keys and data in
+the format used by the \%lsearch%\ lookup (see section ~~SECTsinglekeylookups).
+It writes a DBM file using the lower-cased alias names as keys and the
+remainder of the information as data. The lower-casing can be prevented by
+calling the program with the \-nolc-\ option.
+
+A terminating zero is included as part of the key string. This is expected by
+the \%dbm%\ lookup type. However, if the option \-nozero-\ is given,
+\*exim@_dbmbuild*\ creates files without terminating zeroes in either the key
+strings or the data strings. The \%dbmnz%\ lookup type can be used with such
+files.
+
+The program requires two arguments: the name of the input file (which can be a
+single hyphen to indicate the standard input), and the name of the output file.
+It creates the output under a temporary name, and then renames it if all went
+well.
+.index \\USE@_DB\\
+If the native DB interface is in use (\\USE@_DB\\ is set in a compile-time
+configuration file -- this is common in free versions of Unix) the two file
+names must be different, because in this mode the Berkeley DB functions create
+a single output file using exactly the name given. For example,
+.display asis
+exim_dbmbuild /etc/aliases /etc/aliases.db
+.endd
+reads the system alias file and creates a DBM version of it in
+\(/etc/aliases.db)\.
+
+In systems that use the \*ndbm*\ routines (mostly proprietary versions of Unix),
+two files are used, with the suffixes \(.dir)\ and \(.pag)\. In this
+environment, the suffixes are added to the second argument of
+\*exim@_dbmbuild*\, so it can be the same as the first. This is also the case
+when the Berkeley functions are used in compatibility mode (though this is not
+recommended), because in that case it adds a \(.db)\ suffix to the file name.
+
+If a duplicate key is encountered, the program outputs a warning, and when it
+finishes, its return code is 1 rather than zero, unless the \-noduperr-\ option
+is used. By default, only the first of a set of duplicates is used -- this
+makes it compatible with \%lsearch%\ lookups. There is an option \-lastdup-\
+which causes it to use the data for the last duplicate instead. There is also
+an option \-nowarn-\, which stops it listing duplicate keys to \stderr\. For
+other errors, where it doesn't actually make a new file, the return code is 2.
+
+
+
+.section Finding individual retry times (exinext)
+.rset SECTfinindret "~~chapter.~~section"
+.index retry||times
+.index \*exinext*\
+A utility called \*exinext*\ (mostly a Perl script) provides the ability to fish
+specific information out of the retry database. Given a mail domain (or a
+complete address), it looks up the hosts for that domain, and outputs any retry
+information for the hosts or for the domain. At present, the retry information
+is obtained by running \*exim@_dumpdb*\ (see below) and post-processing the
+output. For example:
+.display asis
+$ exinext piglet@milne.fict.example
+kanga.milne.fict.example:192.168.8.1 error 146: Connection refused
+ first failed: 21-Feb-1996 14:57:34
+ last tried: 21-Feb-1996 14:57:34
+ next try at: 21-Feb-1996 15:02:34
+roo.milne.fict.example:192.168.8.3 error 146: Connection refused
+ first failed: 20-Jan-1996 13:12:08
+ last tried: 21-Feb-1996 11:42:03
+ next try at: 21-Feb-1996 19:42:03
+ past final cutoff time
+.endd
+You can also give \*exinext*\ a local part, without a domain, and it
+will give any retry information for that local part in your default domain.
+A message id can be used to obtain retry information pertaining to a specific
+message. This exists only when an attempt to deliver a message to a remote host
+suffers a message-specific error (see section ~~SECToutSMTPerr). \*exinext*\ is
+not particularly efficient, but then it isn't expected to be run very often.
+
+.em
+The \*exinext*\ utility calls Exim to find out information such as the location
+of the spool directory. The utility has \-C-\ and \-D-\ options, which are
+passed on to the \*exim*\ commands. The first specifies an alternate Exim
+configuration file, and the second sets macros for use within the configuration
+file. These features are mainly to help in testing, but might also be useful in
+environments where more than one configuration file is in use.
+.nem
+
+
+
+.section Hints database maintenance (exim@_dumpdb, exim@_fixdb, exim@_tidydb)
+.rset SECThindatmai "~~chapter.~~section"
+.index hints database||maintenance
+.index maintaining Exim's hints database
+Three utility programs are provided for maintaining the DBM files that Exim
+uses to contain its delivery hint information. Each program requires two
+arguments. The first specifies the name of Exim's spool directory, and the
+second is the name of the database it is to operate on. These are as
+follows:
+.numberpars $.
+\*retry*\: the database of retry information
+.nextp
+\*wait-*\<<transport name>>: databases of information about messages waiting
+for remote hosts
+.nextp
+.em
+\*callout*\: the callout cache
+.nem
+.nextp
+\*misc*\: other hints data
+.endp
+.em
+The \*misc*\ database is used for
+.numberpars alpha
+Serializing \\ETRN\\ runs (when \smtp@_etrn@_serialize\ is set)
+.nextp
+Serializing delivery to a specific host (when \serialize@_hosts\ is set in an
+\%smtp%\ transport)
+.endp
+.nem
+.index \*exim@_dumpdb*\
+The entire contents of a database are written to the standard output by the
+\*exim@_dumpdb*\ program, which has no options or arguments other than the
+spool and database names. For example, to dump the retry database:
+.display asis
+exim_dumpdb /var/spool/exim retry
+.endd
+Two lines of output are produced for each entry:
+.display
+ T:mail.ref.example:192.168.242.242 146 77 Connection refused
+31-Oct-1995 12:00:12 02-Nov-1995 12:21:39 02-Nov-1995 20:21:39 *
+.endd
+The first item on the first line is the key of the record. It starts with one
+of the letters R, or T, depending on whether it refers to a routing or
+transport retry. For a local delivery, the next part is the local address; for
+a remote delivery it is the name of the remote host, followed by its failing IP
+address (unless \no@_retry@_include@_ip@_address\ is set on the \%smtp%\
+transport).
+.em
+If the remote port is not the standard one (port 25), it is added to the IP
+address.
+.nem
+Then there follows an error code, an additional error code, and a
+textual description of the error.
+
+The three times on the second line are the time of first failure, the time of
+the last delivery attempt, and the computed time for the next attempt. The line
+ends with an asterisk if the cutoff time for the last retry rule has been
+exceeded.
+
+Each output line from \*exim@_dumpdb*\ for the \*wait-*\$it{xxx} databases
+consists of a host name followed by a list of ids for messages that are or were
+waiting to be delivered to that host. If there are a very large number for any
+one host, continuation records, with a sequence number added to the host name,
+may be seen. The data in these records is often out of date, because a message
+may be routed to several alternative hosts, and Exim makes no effort to keep
+cross-references.
+
+.index \*exim@_tidydb*\
+The \*exim@_tidydb*\ utility program is used to tidy up the contents of the
+hints databases. If run with no options, it removes all records from a database
+that are more than 30 days old. The cutoff date can be altered by means of the
+\-t-\ option, which must be followed by a time. For example, to remove all
+records older than a week from the retry database:
+.display asis
+exim_tidydb -t 7d /var/spool/exim retry
+.endd
+Both the \*wait-*\$it{xxx} and \*retry*\ databases contain items that involve
+message ids. In the former these appear as data in records keyed by host --
+they were messages that were waiting for that host -- and in the latter they
+are the keys for retry information for messages that have suffered certain
+types of error. When \*exim@_tidydb*\ is run, a check is made to ensure that
+message ids in database records are those of messages that are still on the
+queue. Message ids for messages that no longer exist are removed from
+\*wait-*\$it{xxx} records, and if this leaves any records empty, they are
+deleted. For the \*retry*\ database, records whose keys are non-existent message
+ids are removed. The \*exim@_tidydb*\ utility outputs comments on the standard
+output whenever it removes information from the database.
+
+Removing records from a DBM file does not normally make the file smaller, but
+all the common DBM libraries are able to re-use the space that is released.
+It is therefore suggested that \*exim@_tidydb*\ be run periodically on all the
+hints databases, but at a quiet time of day, because it requires a database to
+be locked (and therefore inaccessible to Exim) while it does its work.
+
+.index \*exim@_fixdb*\
+The \*exim@_fixdb*\ program is a utility for interactively modifying databases.
+Its main use is for testing Exim, but it might also be occasionally useful for
+getting round problems in a live system. It has no options, and its interface
+is somewhat crude. On entry, it prompts for input with a right angle-bracket. A
+key of a database record can then be entered, and the data for that record is
+displayed.
+
+If `d' is typed at the next prompt, the entire record is deleted. For all
+except the \*retry*\ database, that is the only operation that can be carried
+out. For the \*retry*\ database, each field is output preceded by a number, and
+data for individual fields can be changed by typing the field number followed
+by new data, for example:
+.display asis
+> 4 951102:1000
+.endd
+resets the time of the next delivery attempt. Time values are given as a
+sequence of digit pairs for year, month, day, hour, and minute. Colons can be
+used as optional separators.
+
+
+
+.section Mailbox maintenance (exim@_lock)
+.rset SECTmailboxmaint "~~chapter.~~section"
+.index mailbox||maintenance
+.index \*exim@_lock*\
+.index locking mailboxes
+The \*exim@_lock*\ utility locks a mailbox file using the same algorithm as
+Exim. For a discussion of locking issues, see section ~~SECTopappend.
+\*Exim@_lock*\ can be used to prevent any modification of a mailbox by Exim or
+a user agent while investigating a problem. The utility requires the name of
+the file as its first argument. If the locking is successful, the second
+argument is run as a command (using C's \*system()*\ function); if there is no
+second argument, the value of the SHELL environment variable is used; if this
+is unset or empty, \(/bin/sh)\ is run. When the command finishes, the mailbox
+is unlocked and the utility ends. The following options are available:
+
+.startoptions
+
+.option fcntl
+Use \*fcntl()*\ locking on the open mailbox.
+
+.option flock
+Use \*flock()*\ locking on the open mailbox, provided the operating system
+supports it.
+
+.option interval
+This must be followed by a number, which is a number of seconds; it sets the
+interval to sleep between retries (default 3).
+
+.option lockfile
+Create a lock file before opening the mailbox.
+
+.option mbx
+Lock the mailbox using MBX rules.
+
+.option q
+Suppress verification output.
+
+.option retries
+This must be followed by a number; it sets the number of times to try to get
+the lock (default 10).
+
+.option restore@_time
+This option causes \exim@_lock\ to restore the modified and read times to the
+locked file before exiting. This allows you to access a locked mailbox (for
+example, to take a backup copy) without disturbing the times that the user
+subsequently sees.
+
+.option timeout
+This must be followed by a number, which is a number of seconds; it sets a
+timeout to be used with a blocking \*fcntl()*\ lock. If it is not set (the
+default), a non-blocking call is used.
+
+.option v
+Generate verbose output.
+
+.endoptions
+
+If none of \-fcntl-\,
+\-flock-\,
+\-lockfile-\ or \-mbx-\ are given, the default is to create a lock file and
+also to use \*fcntl()*\ locking on the mailbox, which is the same as Exim's
+default. The use of
+\-flock-\
+or \-fcntl-\ requires that the file be writeable; the use of
+\-lockfile-\ requires that the directory containing the file be writeable.
+Locking by lock file does not last for ever; Exim assumes that a lock file is
+expired if it is more than 30 minutes old.
+
+The \-mbx-\ option can be used with either or both of \-fcntl-\ or \-flock-\.
+It assumes \-fcntl-\ by default.
+MBX locking causes a shared lock to be taken out on the open mailbox, and an
+exclusive lock on the file \(/tmp/.$it{n}.$it{m})\ where $it{n} and $it{m} are
+the device number and inode number of the mailbox file. When the locking is
+released, if an exclusive lock can be obtained for the mailbox, the file in
+\(/tmp)\ is deleted.
+
+The default output contains verification of the locking that takes place. The
+\-v-\ option causes some additional information to be given. The \-q-\ option
+suppresses all output except error messages.
+
+A command such as
+.display asis
+exim_lock /var/spool/mail/spqr
+.endd
+runs an interactive shell while the file is locked, whereas
+.display
+exim@_lock -q /var/spool/mail/spqr @<@<End
+<<some commands>>
+End
+.endd
+runs a specific non-interactive sequence of commands while the file is locked,
+suppressing all verification output. A single command can be run by a command
+such as
+.display asis
+exim_lock -q /var/spool/mail/spqr \
+ "cp /var/spool/mail/spqr /some/where"
+.endd
+Note that if a command is supplied, it must be entirely contained within the
+second argument -- hence the quotes.
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter The Exim monitor
+.set runningfoot "monitor"
+.rset CHAPeximon ~~chapter
+.index monitor
+.index Exim monitor
+.index X-windows
+.index \*eximon*\
+.index Local/eximon.conf
+.index \(exim@_monitor/EDITME)\
+The Exim monitor is an application which displays in an X window information
+about the state of Exim's queue and what Exim is doing. An admin user can
+perform certain operations on messages from this GUI interface; however all
+such facilities are also available from the command line, and indeed, the
+monitor itself makes use of the command line to perform any actions requested.
+
+
+.section Running the monitor
+The monitor is started by running the script called \*eximon*\. This is a shell
+script that sets up a number of environment variables, and then runs the
+binary called \(eximon.bin)\. The default appearance of the monitor window can
+be changed by editing the \(Local/eximon.conf)\ file created by editing
+\(exim@_monitor/EDITME)\. Comments in that file describe what the various
+parameters are for.
+
+The parameters that get built into the \*eximon*\ script can be overridden for a
+particular invocation by setting up environment variables of the same names,
+preceded by `$tt{EXIMON@_}'. For example, a shell command such as
+.display asis
+EXIMON_LOG_DEPTH=400 eximon
+.endd
+(in a Bourne-compatible shell) runs \*eximon*\ with an overriding setting of the
+\\LOG@_DEPTH\\ parameter. If \\EXIMON@_LOG@_FILE@_PATH\\ is set in the
+environment, it overrides the Exim log file configuration. This makes it
+possible to have \*eximon*\ tailing log data that is written to syslog, provided
+that MAIL.INFO syslog messages are routed to a file on the local host.
+
+X resources can be used to change the appearance of the window in the normal
+way. For example, a resource setting of the form
+.display asis
+Eximon*background: gray94
+.endd
+changes the colour of the background to light grey rather than white. The
+stripcharts are drawn with both the data lines and the reference lines in
+black. This means that the reference lines are not visible when on top of the
+data. However, their colour can be changed by setting a resource called
+`highlight' (an odd name, but that's what the Athena stripchart widget uses).
+For example, if your X server is running Unix, you could set up lighter
+reference lines in the stripcharts by obeying
+.display asis
+xrdb -merge <<End
+Eximon*highlight: gray
+End
+.endd
+
+.index admin user
+In order to see the contents of messages on the queue, and to operate on them,
+\*eximon*\ must either be run as root or by an admin user.
+
+The monitor's window is divided into three parts. The first contains one or
+more stripcharts and two action buttons, the second contains a `tail' of the
+main log file, and the third is a display of the queue of messages awaiting
+delivery, with two more action buttons. The following sections describe these
+different parts of the display.
+
+
+
+.section The stripcharts
+.index stripchart
+The first stripchart is always a count of messages on the queue. Its name can
+be configured by setting \\QUEUE@_STRIPCHART@_NAME\\ in the
+\(Local/eximon.conf)\ file. The remaining stripcharts are defined in the
+configuration script by regular expression matches on log file entries, making
+it possible to display, for example, counts of messages delivered to certain
+hosts or using certain transports. The supplied defaults display counts of
+received and delivered messages, and of local and SMTP deliveries. The default
+period between stripchart updates is one minute; this can be adjusted by a
+parameter in the \(Local/eximon.conf)\ file.
+
+The stripchart displays rescale themselves automatically as the value they are
+displaying changes. There are always 10 horizontal lines in each chart; the
+title string indicates the value of each division when it is greater than one.
+For example, `x2' means that each division represents a value of 2.
+
+It is also possible to have a stripchart which shows the percentage fullness of
+a particular disk partition, which is useful when local deliveries are confined
+to a single partition.
+.index \statvfs\ function
+This relies on the availability of the \*statvfs()*\ function or equivalent in
+the operating system. Most, but not all versions of Unix that support Exim have
+this. For this particular stripchart, the top of the chart always represents
+100%, and the scale is given as `x10%'. This chart is configured by setting
+\\SIZE@_STRIPCHART\\ and (optionally) \\SIZE@_STRIPCHART@_NAME\\ in the
+\(Local/eximon.conf)\ file.
+
+
+
+.section Main action buttons
+.index size||of monitor window
+.index monitor window size
+.index window size
+Below the stripcharts there is an action button for quitting the monitor. Next
+to this is another button marked `Size'. They are placed here so that shrinking
+the window to its default minimum size leaves just the queue count stripchart
+and these two buttons visible. Pressing the `Size' button causes the window to
+expand to its maximum size, unless it is already at the maximum, in which case
+it is reduced to its minimum.
+
+When expanding to the maximum, if the window cannot be fully seen where it
+currently is, it is moved back to where it was the last time it was at full
+size. When it is expanding from its minimum size, the old position is
+remembered, and next time it is reduced to the minimum it is moved back there.
+
+The idea is that you can keep a reduced window just showing one or two
+stripcharts at a convenient place on your screen, easily expand it to show
+the full window when required, and just as easily put it back to what it was.
+The idea is copied from what the \*twm*\ window manager does for its
+\*f.fullzoom*\ action. The minimum size of the window can be changed by setting
+the \\MIN@_HEIGHT\\ and \\MIN@_WIDTH\\ values in \(Local/eximon.conf)\.
+
+Normally, the monitor starts up with the window at its full size, but it can be
+built so that it starts up with the window at its smallest size, by setting
+\\START@_SMALL\\=yes in \(Local/eximon.conf)\.
+
+
+.section The log display
+.index log||tail of, in monitor
+The second section of the window is an area in which a display of the tail of
+the main log is maintained.
+To save space on the screen, the timestamp on each log line is shortened by
+removing the date and, if \log@_timezone\ is set, the timezone.
+The log tail is not available when the only destination for logging data is
+syslog, unless the syslog lines are routed to a local file whose name is passed
+to \*eximon*\ via the \\EXIMON@_LOG@_FILE@_PATH\\ environment variable.
+
+The log sub-window has a scroll bar at its lefthand side which can be used to
+move back to look at earlier text, and the up and down arrow keys also have a
+scrolling effect. The amount of log that is kept depends on the setting of
+\\LOG@_BUFFER\\ in \(Local/eximon.conf)\, which specifies the amount of memory
+to use. When this is full, the earlier 50% of data is discarded -- this is much
+more efficient than throwing it away line by line. The sub-window also has a
+horizontal scroll bar for accessing the ends of long log lines. This is the
+only means of horizontal scrolling; the right and left arrow keys are not
+available. Text can be cut from this part of the window using the mouse in the
+normal way. The size of this subwindow is controlled by parameters in the
+configuration file \(Local/eximon.conf)\.
+
+Searches of the text in the log window can be carried out by means of the ^R
+and ^S keystrokes, which default to a reverse and a forward search,
+respectively. The search covers only the text that is displayed in the window.
+It cannot go further back up the log.
+
+The point from which the search starts is indicated by a caret marker. This is
+normally at the end of the text in the window, but can be positioned explicitly
+by pointing and clicking with the left mouse button, and is moved automatically
+by a successful search. If new text arrives in the window when it is scrolled
+back, the caret remains where it is, but if the window is not scrolled back,
+the caret is moved to the end of the new text.
+
+Pressing ^R or ^S pops up a window into which the search text can be typed.
+There are buttons for selecting forward or reverse searching, for carrying out
+the search, and for cancelling. If the `Search' button is pressed, the search
+happens and the window remains so that further searches can be done. If the
+`Return' key is pressed, a single search is done and the window is closed. If
+^C is typed the search is cancelled.
+
+The searching facility is implemented using the facilities of the Athena text
+widget. By default this pops up a window containing both `search' and `replace'
+options. In order to suppress the unwanted `replace' portion for eximon, a
+modified version of the \TextPop\ widget is distributed with Exim. However, the
+linkers in BSDI and HP-UX seem unable to handle an externally provided version
+of \TextPop\ when the remaining parts of the text widget come from the standard
+libraries. The compile-time option \\EXIMON@_TEXTPOP\\ can be unset to cut out
+the modified \TextPop\, making it possible to build Eximon on these systems, at
+the expense of having unwanted items in the search popup window.
+
+
+.section The queue display
+.index queue||display in monitor
+The bottom section of the monitor window contains a list of all messages that
+are on the queue, which includes those currently being received or delivered,
+as well as those awaiting delivery. The size of this subwindow is controlled by
+parameters in the configuration file \(Local/eximon.conf)\, and the frequency
+at which it is updated is controlled by another parameter in the same file --
+the default is 5 minutes, since queue scans can be quite expensive. However,
+there is an `Update' action button just above the display which can be used to
+force an update of the queue display at any time.
+
+When a host is down for some time, a lot of pending mail can build up for it,
+and this can make it hard to deal with other messages on the queue. To help
+with this situation there is a button next to `Update' called `Hide'. If
+pressed, a dialogue box called `Hide addresses ending with' is put up. If you
+type anything in here and press `Return', the text is added to a chain of such
+texts, and if every undelivered address in a message matches at least one
+of the texts, the message is not displayed.
+
+If there is an address that does not match any of the texts, all the addresses
+are displayed as normal. The matching happens on the ends of addresses so, for
+example, \*cam.ac.uk*\ specifies all addresses in Cambridge, while
+\*xxx@@foo.com.example*\ specifies just one specific address. When any hiding
+has been set up, a button called `Unhide' is displayed. If pressed, it cancels
+all hiding. Also, to ensure that hidden messages do not get forgotten, a hide
+request is automatically cancelled after one hour.
+
+While the dialogue box is displayed, you can't press any buttons or do anything
+else to the monitor window. For this reason, if you want to cut text from the
+queue display to use in the dialogue box, you have to do the cutting before
+pressing the `Hide' button.
+
+The queue display contains, for each unhidden queued message, the length of
+time it has been on the queue, the size of the message, the message id, the
+message sender, and the first undelivered recipient, all on one line. If it is
+a bounce message, the sender is shown as `<>'. If there is more than one
+recipient to which the message has not yet been delivered, subsequent ones are
+listed on additional lines, up to a maximum configured number, following which
+an ellipsis is displayed. Recipients that have already received the message are
+not shown.
+.index frozen messages||display
+If a message is frozen, an asterisk is displayed at the left-hand side.
+
+The queue display has a vertical scroll bar, and can also be scrolled by means
+of the arrow keys. Text can be cut from it using the mouse in the normal way.
+The text searching facilities, as described above for the log window, are also
+available, but the caret is always moved to the end of the text when the queue
+display is updated.
+
+
+.section The queue menu
+.index queue||menu in monitor
+If the \shift\ key is held down and the left button is clicked when the mouse
+pointer is over the text for any message, an action menu pops up, and the first
+line of the queue display for the message is highlighted. This does not affect
+any selected text.
+
+If you want to use some other event for popping up the menu, you can set the
+\\MENU@_EVENT\\ parameter in \(Local/eximon.conf)\ to change the default, or
+set \\EXIMON@_MENU@_EVENT\\ in the environment before starting the monitor. The
+value set in this parameter is a standard X event description. For example, to
+run eximon using \ctrl\ rather than \shift\ you could use
+.display asis
+EXIMON_MENU_EVENT='Ctrl<Btn1Down>' eximon
+.endd
+The title of the menu is the message id, and it contains entries which act as
+follows:
+.numberpars $.
+\*message log*\: The contents of the message log for the message are displayed in
+a new text window.
+.nextp
+\*headers*\: Information from the spool file that contains the envelope
+information and headers is displayed in a new text window. See chapter
+~~CHAPspool for a description of the format of spool files.
+.nextp
+\*body*\: The contents of the spool file containing the body of the message are
+displayed in a new text window. There is a default limit of 20,000 bytes to the
+amount of data displayed. This can be changed by setting the \\BODY@_MAX\\
+option at compile time, or the \\EXIMON@_BODY@_MAX\\ option at run time.
+.nextp
+\*deliver message*\: A call to Exim is made using the \-M-\ option to request
+delivery of the message. This causes an automatic thaw if the message is
+frozen. The \-v-\ option is also set, and the output from Exim is displayed in
+a new text window. The delivery is run in a separate process, to avoid holding
+up the monitor while the delivery proceeds.
+.nextp
+\*freeze message*\: A call to Exim is made using the \-Mf-\ option to request
+that the message be frozen.
+.nextp
+.index thawing messages
+.index unfreezing messages
+.index frozen messages||thawing
+\*thaw message*\: A call to Exim is made using the \-Mt-\ option to request that
+the message be thawed.
+.nextp
+.index delivery||forcing failure
+\*give up on msg*\: A call to Exim is made using the \-Mg-\ option to request
+that Exim gives up trying to deliver the message. A bounce message is generated
+for any remaining undelivered addresses.
+.nextp
+\*remove message*\: A call to Exim is made using the \-Mrm-\ option to request
+that the message be deleted from the system without generating a bounce
+message.
+.nextp
+\*add recipient*\: A dialog box is displayed into which a recipient address can
+be typed. If the address is not qualified and the \\QUALIFY@_DOMAIN\\ parameter
+is set in \(Local/eximon.conf)\, the address is qualified with that domain.
+Otherwise it must be entered as a fully qualified address. Pressing \\RETURN\\
+causes a call to Exim to be made using the \-Mar-\ option to request that an
+additional recipient be added to the message, unless the entry box is empty, in
+which case no action is taken.
+.nextp
+\*mark delivered*\: A dialog box is displayed into which a recipient address can
+be typed. If the address is not qualified and the \\QUALIFY@_DOMAIN\\ parameter
+is set in \(Local/eximon.conf)\, the address is qualified with that domain.
+Otherwise it must be entered as a fully qualified address. Pressing \\RETURN\\
+causes a call to Exim to be made using the \-Mmd-\ option to mark the given
+recipient address as already delivered, unless the entry box is empty, in which
+case no action is taken.
+.nextp
+\*mark all delivered*\: A call to Exim is made using the \-Mmad-\ option to mark
+all recipient addresses as already delivered.
+.nextp
+\*edit sender*\: A dialog box is displayed initialized with the current sender's
+address. Pressing \\RETURN\\ causes a call to Exim to be made using the \-Mes-\
+option to replace the sender address, unless the entry box is empty, in which
+case no action is taken. If you want to set an empty sender (as in bounce
+messages), you must specify it as `<>'. Otherwise, if the address is not
+qualified and the \\QUALIFY@_DOMAIN\\ parameter is set in
+\(Local/eximon.conf)\, the address is qualified with that domain.
+.endp
+When a delivery is forced, a window showing the \-v-\ output is displayed. In
+other cases when a call to Exim is made, if there is any output from Exim (in
+particular, if the command fails) a window containing the command and the
+output is displayed. Otherwise, the results of the action are normally apparent
+from the log and queue displays. However, if you set \\ACTION@_OUTPUT\\=yes in
+\(Local/eximon.conf)\, a window showing the Exim command is always opened, even
+if no output is generated.
+
+The queue display is automatically updated for actions such as freezing and
+thawing, unless \\ACTION@_QUEUE@_UPDATE\\=no has been set in
+\(Local/eximon.conf)\. In this case the `Update' button has to be used to force
+an update of the display after one of these actions.
+
+In any text window that is displayed as result of a menu action, the normal
+cut-and-paste facility is available, and searching can be carried out using ^R
+and ^S, as described above for the log tail window.
+
+
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Security considerations
+.set runningfoot "security"
+.rset CHAPsecurity ~~chapter
+.index security
+This chapter discusses a number of issues concerned with security, some of
+which are also covered in other parts of this manual.
+
+For reasons that this author does not understand, some people have promoted
+Exim as a `particularly secure' mailer. Perhaps it is because of the existence
+of this chapter in the documentation. However, the intent of the chapter is
+simply to describe the way Exim works in relation to certain security concerns,
+not to make any specific claims about the effectiveness of its security as
+compared with other MTAs.
+
+What follows is a description of the way Exim is supposed to be. Best efforts
+have been made to try to ensure that the code agrees with the theory, but an
+absence of bugs can never be guaranteed. Any that are reported will get fixed
+as soon as possible.
+
+.section Building a more `hardened' Exim
+.index security||build-time features
+There are a number of build-time options that can be set in \(Local/Makefile)\
+to create Exim binaries that are `harder' to attack, in particular by a rogue
+Exim administrator who does not have the root password, or by someone who has
+penetrated the Exim (but not the root) account. These options are as follows:
+.numberpars $.
+\\ALT@_CONFIG@_PREFIX\\ can be set to a string that is required to match the
+start of any file names used with the \-C-\ option. When it is set, these file
+names are also not allowed to contain the sequence `/../'. (However, if the
+value of the \-C-\ option is identical to the value of \\CONFIGURE@_FILE\\ in
+\(Local/Makefile)\, Exim ignores \-C-\ and proceeds as usual.) There is no
+default setting for \ALT@_CONFIG@_PREFIX\.
+
+If the permitted configuration files are confined to a directory to
+which only root has access, this guards against someone who has broken
+into the Exim account from running a privileged Exim with an arbitrary
+configuration file, and using it to break into other accounts.
+.nextp
+If \\ALT@_CONFIG@_ROOT@_ONLY\\ is defined, root privilege is retained for \-C-\
+and \-D-\ only if the caller of Exim is root. Without it, the Exim user may
+also use \-C-\ and \-D-\ and retain privilege. Setting this option locks out
+the possibility of testing a configuration using \-C-\ right through message
+reception and delivery, even if the caller is root. The reception works, but by
+that time, Exim is running as the Exim user, so when it re-execs to regain
+privilege for the delivery, the use of \-C-\ causes privilege to be lost.
+However, root can test reception and delivery using two separate commands.
+\\ALT@_CONFIG@_ROOT@_ONLY\\ is not set by default.
+.nextp
+If \\DISABLE@_D@_OPTION\\ is defined, the use of the \-D-\ command line option
+is disabled.
+.nextp
+\\FIXED@_NEVER@_USERS\\ can be set to a colon-separated list of users that are
+never to be used for any deliveries. This is like the \never@_users\ runtime
+option, but it cannot be overridden; the runtime option adds additional users
+to the list. The default setting is `root'; this prevents a non-root user who
+is permitted to modify the runtime file from using Exim as a way to get root.
+.endp
+
+
+.section Root privilege
+.index setuid
+.index root privilege
+The Exim binary is normally setuid to root, which means that it gains root
+privilege (runs as root) when it starts execution. In some special cases (for
+example, when the daemon is not in use and there are no local deliveries), it
+may be possible to run Exim setuid to some user other than root. This is
+discussed in the next section. However, in most installations, root privilege
+is required for two things:
+.numberpars $.
+To set up a socket connected to the standard SMTP port (25) when initialising
+the listening daemon. If Exim is run from \*inetd*\, this privileged action is
+not required.
+.nextp
+To be able to change uid and gid in order to read users' \(.forward)\ files and
+perform local deliveries as the receiving user or as specified in the
+configuration.
+.endp
+It is not necessary to be root to do any of the other things Exim does, such as
+receiving messages and delivering them externally over SMTP, and it is
+obviously more secure if Exim does not run as root except when necessary.
+For this reason, a user and group for Exim to use must be defined in
+\(Local/Makefile)\. These are known as `the Exim user' and `the Exim group'.
+Their values can be changed by the run time configuration, though this is not
+recommended. Often a user called \*exim*\ is used, but some sites use \*mail*\
+or another user name altogether.
+
+Exim uses \*setuid()*\ whenever it gives up root privilege. This is a permanent
+abdication; the process cannot regain root afterwards. Prior to release 4.00,
+\*seteuid()*\ was used in some circumstances, but this is no longer the case.
+
+After a new Exim process has interpreted its command line options, it changes
+uid and gid in the following cases:
+.numberpars $.
+.index \-C-\ option
+.index \-D-\ option
+If the \-C-\ option is used to specify an alternate configuration file, or if
+the \-D-\ option is used to define macro values for the configuration, and the
+calling process is not running as root or the Exim user, the uid and gid are
+changed to those of the calling process.
+However, if \\ALT@_CONFIG@_ROOT@_ONLY\\ is defined in \(Local/Makefile)\, only
+root callers may use \-C-\ and \-D-\ without losing privilege, and if
+\\DISABLE@_D@_OPTION\\ is set, the \-D-\ option may not be used at all.
+.nextp
+.index \-be-\ option
+.index \-bf-\ option
+.index \-bF-\ option
+If the expansion test option (\-be-\) or one of the filter testing options
+(\-bf-\ or \-bF-\) are used, the uid and gid are changed to those of the
+calling process.
+.nextp
+If the process is not a daemon process or a queue runner process or a delivery
+process or a process for testing address routing (started with \-bt-\), the uid
+and gid are changed to the Exim user and group. This means that Exim always
+runs under its own uid and gid when receiving messages. This also applies when
+testing address verification
+.index \-bv-\ option
+.index \-bh-\ option
+(the \-bv-\ option) and testing incoming message policy controls (the \-bh-\
+option).
+.nextp
+For a daemon, queue runner, delivery, or address testing process, the uid
+remains as root at this stage, but the gid is changed to the Exim group.
+.endp
+The processes that initially retain root privilege behave as follows:
+.numberpars $.
+A daemon process changes the gid to the Exim group and the uid to the Exim user
+after setting up one or more listening sockets. The \*initgroups()*\ function
+is called, so that if the Exim user is in any additional groups, they will be
+used during message reception.
+.nextp
+A queue runner process retains root privilege throughout its execution. Its job
+is to fork a controlled sequence of delivery processes.
+.nextp
+A delivery process retains root privilege throughout most of its execution,
+but any actual deliveries (that is, the transports themselves) are run in
+subprocesses which always change to a non-root uid and gid. For local
+deliveries this is typically the uid and gid of the owner of the mailbox; for
+remote deliveries, the Exim uid and gid are used. Once all the delivery
+subprocesses have been run, a delivery process changes to the Exim uid and gid
+while doing post-delivery tidying up such as updating the retry database and
+generating bounce and warning messages.
+
+While the recipient addresses in a message are being routed, the delivery
+process runs as root. However, if a user's filter file has to be processed,
+this is done in a subprocess that runs under the individual user's uid and
+gid. A system filter is run as root unless \system@_filter@_user\ is set.
+.nextp
+A process that is testing addresses (the \-bt-\ option) runs as root so that
+the routing is done in the same environment as a message delivery.
+.endp
+
+
+.section Running Exim without privilege
+.index privilege, running without
+.index unprivileged running
+.index root privilege||running without
+Some installations like to run Exim in an unprivileged state for more of its
+operation, for added security. Support for this mode of operation is provided
+by the global option \deliver@_drop@_privilege\. When this is set, the uid and
+gid are changed to the Exim user and group at the start of a delivery process
+(and also queue runner and address testing processes). This means that address
+routing is no longer run as root, and the deliveries themselves cannot change
+to any other uid.
+
+Leaving the binary setuid to root, but setting \deliver@_drop@_privilege\ means
+that the daemon can still be started in the usual way, and it can respond
+correctly to SIGHUP because the re-invocation regains root privilege.
+
+An alternative approach is to make Exim setuid to the Exim user and also setgid
+to the Exim group.
+If you do this, the daemon must be started from a root process. (Calling
+Exim from a root process makes it behave in the way it does when it is setuid
+root.) However, the daemon cannot restart itself after a SIGHUP signal because
+it cannot regain privilege.
+
+It is still useful to set \deliver@_drop@_privilege\ in this case, because it
+stops Exim from trying to re-invoke itself to do a delivery after a message has
+been received. Such a re-invocation is a waste of resources because it has no
+effect.
+
+If restarting the daemon is not an issue (for example, if \*inetd*\ is being
+used instead of a daemon), having the binary setuid to the Exim user seems a
+clean approach, but there is one complication:
+
+In this style of operation, Exim is running with the real uid and gid set to
+those of the calling process, and the effective uid/gid set to Exim's values.
+Ideally, any association with the calling process' uid/gid should be dropped,
+that is, the real uid/gid should be reset to the effective values so as to
+discard any privileges that the caller may have. While some operating systems
+have a function that permits this action for a non-root effective uid, quite a
+number of them do not. Because of this lack of standardization, Exim does not
+address this problem at this time.
+
+For this reason, the recommended approach for `mostly unprivileged' running is
+to keep the Exim binary setuid to root, and to set \deliver@_drop@_privilege\.
+This also has the advantage of allowing a daemon to be used in the most
+straightforward way.
+
+If you configure Exim not to run delivery processes as root, there are a
+number of restrictions on what you can do:
+.numberpars $.
+You can deliver only as the Exim user/group. You should explicitly use the
+\user\ and \group\ options to override routers or local transports that
+normally deliver as the recipient. This makes sure that configurations that
+work in this mode function the same way in normal mode. Any implicit or
+explicit specification of another user causes an error.
+.nextp
+Use of \(.forward)\ files is severely restricted, such that it is usually
+not worthwhile to include them in the configuration.
+.nextp
+Users who wish to use \(.forward)\ would have to make their home directory and
+the file itself accessible to the Exim user. Pipe and append-to-file entries,
+and their equivalents in Exim filters, cannot be used. While they could be
+enabled in the Exim user's name, that would be insecure and not very useful.
+.nextp
+Unless the local user mailboxes are all owned by the Exim user (possible in
+some POP3 or IMAP-only environments):
+.numberpars $*$
+They must be owned by the Exim group and be writable by that group. This
+implies you must set \mode\ in the appendfile configuration, as well as the
+mode of the mailbox files themselves.
+.nextp
+You must set \no@_check@_owner\, since most or all of the files will not be
+owned by the Exim user.
+.nextp
+You must set \file@_must@_exist\, because Exim cannot set the owner correctly
+on a newly created mailbox when unprivileged. This also implies that new
+mailboxes need to be created manually.
+.endp
+.endp
+These restrictions severely restrict what can be done in local deliveries.
+However, there are no restrictions on remote deliveries. If you are running a
+gateway host that does no local deliveries, setting \deliver@_drop@_privilege\
+gives more security at essentially no cost.
+
+
+.section Delivering to local files
+Full details of the checks applied by \%appendfile%\ before it writes to a file
+are given in chapter ~~CHAPappendfile.
+
+
+.section IPv4 source routing
+.index source routing||in IP packets
+.index IP source routing
+Many operating systems suppress IP source-routed packets in the kernel, but
+some cannot be made to do this, so Exim does its own check. It logs incoming
+IPv4 source-routed TCP calls, and then drops them. Things are all different in
+IPv6. No special checking is currently done.
+
+
+.section The VRFY, EXPN, and ETRN commands in SMTP
+Support for these SMTP commands is disabled by default. If required, they can
+be enabled by defining suitable ACLs.
+
+
+
+.section Privileged users
+.index trusted user
+.index admin user
+.index privileged user
+.index user||trusted
+.index user||admin
+Exim recognises two sets of users with special privileges. Trusted users are
+able to submit new messages to Exim locally, but supply their own sender
+addresses and information about a sending host. For other users submitting
+local messages, Exim sets up the sender address from the uid, and doesn't
+permit a remote host to be specified.
+
+.index \-f-\ option
+However, an untrusted user is permitted to use the \-f-\ command line option in
+the special form \-f @<@>-\ to indicate that a delivery failure for the message
+should not cause an error report. This affects the message's envelope, but it
+does not affect the ::Sender:: header. Untrusted users may also be permitted to
+use specific forms of address with the \-f-\ option by setting the
+\untrusted@_set@_sender\ option.
+
+Trusted users are used to run processes that receive mail messages from some
+other mail domain and pass them on to Exim for delivery either locally, or over
+the Internet. Exim trusts a caller that is running as root, as the Exim user,
+as any user listed in the \trusted@_users\ configuration option, or under any
+group listed in the \trusted@_groups\ option.
+
+Admin users are permitted to do things to the messages on Exim's queue. They
+can freeze or thaw messages, cause them to be returned to their senders, remove
+them entirely, or modify them in various ways. In addition, admin users can run
+the Exim monitor and see all the information it is capable of providing, which
+includes the contents of files on the spool.
+
+.index \-M-\ option
+.index \-q-\ option
+By default, the use of the \-M-\ and \-q-\ options to cause Exim to attempt
+delivery of messages on its queue is restricted to admin users. This
+restriction can be relaxed by setting the \no@_prod@_requires@_admin\ option.
+Similarly, the use of \-bp-\ (and its variants) to list the contents of the
+queue is also restricted to admin users. This restriction can be relaxed by
+setting \no@_queue@_list@_requires@_admin\.
+
+Exim recognises an admin user if the calling process is running as root or as
+the Exim user or if any of the groups associated with the calling process is
+the Exim group. It is not necessary actually to be running under the Exim
+group. However, if admin users who are not root or the Exim user are to access
+the contents of files on the spool via the Exim monitor (which runs
+unprivileged), Exim must be built to allow group read access to its spool
+files.
+
+
+.section Spool files
+.index spool directory||files
+Exim's spool directory and everything it contains is owned by the Exim user and
+set to the Exim group. The mode for spool files is defined in the
+\(Local/Makefile)\ configuration file, and defaults to 0640. This means that
+any user who is a member of the Exim group can access these files.
+
+
+.section Use of argv[0]
+Exim examines the last component of \argv[0]\, and if it matches one of a set
+of specific strings, Exim assumes certain options. For example, calling Exim
+with the last component of \argv[0]\ set to `rsmtp' is exactly equivalent to
+calling it with the option \-bS-\. There are no security implications in this.
+
+
+.section Use of %f formatting
+The only use made of `%f' by Exim is in formatting load average values. These
+are actually stored in integer variables as 1000 times the load average.
+Consequently, their range is limited and so therefore is the length of the
+converted output.
+
+
+.section Embedded Exim path
+Exim uses its own path name, which is embedded in the code, only when it needs
+to re-exec in order to regain root privilege. Therefore, it is not root when it
+does so. If some bug allowed the path to get overwritten, it would lead to an
+arbitrary program's being run as exim, not as root.
+
+
+.section Use of sprintf()
+.index \*sprintf()*\
+A large number of occurrences of `sprintf' in the code are actually calls to
+\*string@_sprintf()*\, a function that returns the result in malloc'd store.
+The intermediate formatting is done into a large fixed buffer by a function
+that runs through the format string itself, and checks the length of each
+conversion before performing it, thus preventing buffer overruns.
+
+The remaining uses of \*sprintf()*\ happen in controlled circumstances where
+the output buffer is known to be sufficiently long to contain the converted
+string.
+
+
+.section Use of debug@_printf() and log@_write()
+Arbitrary strings are passed to both these functions, but they do their
+formatting by calling the function \*string@_vformat()*\, which runs through
+the format string itself, and checks the length of each conversion.
+
+
+.section Use of strcat() and strcpy()
+These are used only in cases where the output buffer is known to be large
+enough to hold the result.
+
+
+
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Format of spool files
+.set runningfoot "spool file format"
+.rset CHAPspool ~~chapter
+.index format||spool files
+.index spool directory||format of files
+.index spool||files, format of
+.index spool||files, editing
+A message on Exim's queue consists of two files, whose names are the message id
+followed by -D and -H, respectively. The data portion of the message is kept in
+the -D file on its own. The message's envelope, status, and headers are all
+kept in the -H file, whose format is described in this chapter. Each of these
+two files contains the final component of its own name as its first line. This
+is insurance against disk crashes where the directory is lost but the files
+themselves are recoverable.
+
+.em
+Some people are tempted into editing -D files in order to modify messages. You
+need to be extremely careful if you do this; it is not recommended and you are
+on your own if you do it. Here are some of the pitfalls:
+.numberpars $.
+You must use the \*exim@_lock*\ utility to ensure that Exim does not try to
+deliver the message while you are fiddling with it. The lock is implemented
+by opening the -D file and taking out a write lock on it. If you update the
+file in place, the lock will be retained. If you write a new file and rename
+it, the lock will be lost at the instant of rename.
+.nextp
+If you change the number of lines in the file, the value of
+\$body@_linecount$\, which is stored in the -H file, will be incorrect.
+.nextp
+If the message is in MIME format, you must take care not to break it.
+.nextp
+If the message is cryptographically signed, any change will invalidate the
+signature.
+.endp
+.nem
+
+Files whose names end with -J may also be seen in the \(input)\ directory (or
+its subdirectories when \split@_spool@_directory\ is set). These are journal
+files, used to record addresses to which the message has been delivered during
+the course of a delivery run. At the end of the run, the -H file is updated,
+and the -J file is deleted.
+
+.section Format of the -H file
+.index uid (user id)||in spool file
+.index gid (group id)||in spool file
+The second line of the -H file contains the login name for the uid of the
+process that called Exim to read the message, followed by the numerical uid and
+gid. For a locally generated message, this is normally the user who sent the
+message. For a message received over TCP/IP, it is normally the Exim user.
+
+The third line of the file contains the address of the message's sender as
+transmitted in the envelope, contained in angle brackets. The sender address is
+empty for bounce messages. For incoming SMTP mail, the sender address is given
+in the \\MAIL\\ command. For locally generated mail, the sender address is
+created by Exim from the login name of the current user and the configured
+\qualify@_domain\. However, this can be overridden by the \-f-\ option or a
+leading `From' line if the caller is trusted, or if the supplied address is
+`@<@>' or an address that matches \untrusted@_set@_senders\.
+
+The fourth line contains two numbers. The first is the time that the message
+was received, in the conventional Unix form -- the number of seconds since the
+start of the epoch. The second number is a count of the number of messages
+warning of delayed delivery that have been sent to the sender.
+
+There follow a number of lines starting with a hyphen. These can appear in any
+order, and are omitted when not relevant:
+.numberpars $.
+.em
+\-acl <<number>> <<length>>-\: A line of this form is present for every ACL
+variable that is not empty. The number identifies the variable; the
+\acl@_c\*x*\$$\ variables are numbered 0--9 and the \acl@_m\*x*\$$\ variables
+are numbered 10--19. The length is the length of the data string for the
+variable. The string itself starts at the beginning of the next line, and is
+followed by a newline character. It may contain internal newlines.
+.nextp
+\-allow@_unqualified@_recipient-\: This is present if unqualified recipient
+addresses are permitted in header lines (to stop such addresses from being
+qualified if rewriting occurs at transport time). Local messages that were
+input using \-bnq-\ and remote messages from hosts that match
+\recipient@_unqualified@_hosts\ set this flag.
+.nextp
+\-allow@_unqualified@_sender-\: This is present if unqualified sender
+addresses are permitted in header lines (to stop such addresses from being
+qualified if rewriting occurs at transport time). Local messages that were
+input using \-bnq-\ and remote messages from hosts that match
+\sender@_unqualified@_hosts\ set this flag.
+.nem
+.nextp
+\-auth@_id <<text>>-\: The id information for a message received on an
+authenticated SMTP connection -- the value of the \$authenticated@_id$\
+variable.
+.nextp
+\-auth@_sender <<address>>-\: The address of an authenticated sender -- the
+value of the \$authenticated@_sender$\ variable.
+.nextp
+\-body@_linecount <<number>>-\: This records the number of lines in the body of
+the message, and is always present.
+.nextp
+\-deliver@_firsttime-\: This is written when a new message is first added to
+the spool. When the spool file is updated after a deferral, it is omitted.
+.nextp
+.index frozen messages||spool data
+\-frozen <<time>>-\: The message is frozen, and the freezing happened at
+<<time>>.
+.nextp
+\-helo@_name <<text>>-\: This records the host name as specified by a remote
+host in a \\HELO\\ or \\EHLO\\ command.
+.nextp
+\-host@_address <<address>>.<<port>>-\: This records the IP address of the host
+from which the message was received and the remote port number that was used.
+It is omitted for locally generated messages.
+.nextp
+\-host@_auth <<text>>-\: If the message was received on an authenticated SMTP
+connection, this records the name of the authenticator -- the value of the
+\$sender@_host@_authenticated$\ variable.
+.nextp
+\-host@_lookup@_failed-\: This is present if an attempt to look up the sending
+host's name from its IP address failed. It corresponds to the
+\$host@_lookup@_failed$\ variable.
+.nextp
+.index DNS||reverse lookup
+.index reverse DNS lookup
+\-host@_name <<text>>-\: This records the name of the remote host from which
+the message was received, if the host name was looked up from the IP address
+when the message was being received. It is not present if no reverse lookup was
+done.
+.nextp
+\-ident <<text>>-\: For locally submitted messages, this records the login of
+the originating user, unless it was a trusted user and the \-oMt-\ option was
+used to specify an ident value. For messages received over TCP/IP, this records
+the ident string supplied by the remote host, if any.
+.nextp
+\-interface@_address <<address>>.<<port>>-\: This records the IP address of the
+local interface and the port number through which a message was received from a
+remote host. It is omitted for locally generated messages.
+.nextp
+\-local-\: The message is from a local sender.
+.nextp
+\-localerror-\: The message is a locally-generated bounce message.
+.nextp
+\-local@_scan <<string>>-\: This records the data string that was
+returned by the \*local@_scan()*\ function when the message was received -- the
+value of the \$local@_scan@_data$\ variable. It is omitted if no data was
+returned.
+.nextp
+\-manual@_thaw-\: The message was frozen but has been thawed manually, that is,
+by an explicit Exim command rather than via the auto-thaw process.
+.nextp
+\-N-\: A testing delivery process was started using the \-N-\ option to
+suppress any actual deliveries, but delivery was deferred. At any further
+delivery attempts, \-N-\ is assumed.
+.nextp
+\-received@_protocol-\: This records the value of the \$received@_protocol$\
+variable, which contains the name of the protocol by which the message was
+received.
+.nextp
+\-sender@_set@_untrusted-\: The envelope sender of this message was set by an
+untrusted local caller (used to ensure that the caller is displayed in queue
+listings).
+.nextp
+\-tls@_certificate@_verified-\: A TLS certificate was received from the client
+that sent this message, and the certificate was verified by the server.
+.nextp
+\-tls@_cipher <<cipher name>>-\: When the message was received over an
+encrypted connection, this records the name of the cipher suite that was used.
+.nextp
+\-tls@_peerdn <<peer DN>>-\: When the message was received over an encrypted
+connection, and a certificate was received from the client, this records the
+Distinguished Name from that certificate.
+.endp
+
+Following the options there is a list of those addresses to which the message
+is not to be delivered. This set of addresses is initialized from the command
+line when the \-t-\ option is used and \extract__addresses__remove__arguments\
+is set; otherwise it starts out empty. Whenever a successful delivery is made,
+the address is added to this set. The addresses are kept internally as a
+balanced binary tree, and it is a representation of that tree which is written
+to the spool file. If an address is expanded via an alias or forward file, the
+original address is added to the tree when deliveries to all its child
+addresses are complete.
+
+If the tree is empty, there is a single line in the spool file containing just
+the text `XX'. Otherwise, each line consists of two letters, which are either Y
+or N, followed by an address. The address is the value for the node of the
+tree, and the letters indicate whether the node has a left branch and/or a
+right branch attached to it, respectively. If branches exist, they immediately
+follow. Here is an example of a three-node tree:
+.display asis
+YY darcy@austen.fict.example
+NN alice@wonderland.fict.example
+NN editor@thesaurus.ref.example
+.endd
+After the non-recipients tree, there is a list of the message's recipients.
+This is a simple list, preceded by a count. It includes all the original
+recipients of the message, including those to whom the message has already been
+delivered. In the simplest case, the list contains one address per line. For
+example:
+.display asis
+4
+editor@thesaurus.ref.example
+darcy@austen.fict.example
+rdo@foundation
+alice@wonderland.fict.example
+.endd
+However, when a child address has been added to the top-level addresses as a
+result of the use of the \one@_time\ option on a \%redirect%\ router, each line
+is of the following form:
+.display
+<<top-level address>> <<errors@_to address>> <<length>>,<<parent number>>@#<<flag bits>>
+.endd
+The 01 flag bit indicates the presence of the three other fields that follow
+the top-level address. Other bits may be used in future to support additional
+fields. The <<parent number>> is the offset in the recipients list of the
+original parent of the `one time' address. The first two fields are the
+envelope sender that is associated with this address and its length. If the
+length is zero, there is no special envelope sender (there are then two space
+characters in the line). A non-empty field can arise from a \%redirect%\ router
+that has an \errors@_to\ setting.
+
+
+A blank line separates the envelope and status information from the headers
+which follow. A header may occupy several lines of the file, and to save effort
+when reading it in, each header is preceded by a number and an identifying
+character. The number is the number of characters in the header, including any
+embedded newlines and the terminating newline. The character is one of the
+following:
+.display
+.tabs 9
+<<blank>> $t $rm{header in which Exim has no special interest}
+#B $t $rm{::Bcc:: header}
+#C $t $rm{::Cc:: header}
+#F $t $rm{::From:: header}
+#I $t $rm{::Message-id:: header}
+#P $t $rm{::Received:: header -- P for `postmark'}
+#R $t $rm{::Reply-To:: header}
+#S $t $rm{::Sender:: header}
+#T $t $rm{::To:: header}
+#* $t $rm{replaced or deleted header}
+.endd
+Deleted or replaced (rewritten) headers remain in the spool file for debugging
+purposes. They are not transmitted when the message is delivered. Here is a
+typical set of headers:
+.display asis
+111P Received: by hobbit.fict.example with local (Exim 4.00)
+ id 14y9EI-00026G-00; Fri, 11 May 2001 10:28:59 +0100
+049 Message-Id: <E14y9EI-00026G-00@hobbit.fict.example>
+038* X-rewrote-sender: bb@hobbit.fict.example
+042* From: Bilbo Baggins <bb@hobbit.fict.example>
+049F From: Bilbo Baggins <B.Baggins@hobbit.fict.example>
+099* To: alice@wonderland.fict.example, rdo@foundation,
+ darcy@austen.fict.example, editor@thesaurus.ref.example
+109T To: alice@wonderland.fict.example, rdo@foundation.fict.example,
+ darcy@austen.fict.example, editor@thesaurus.ref.example
+038 Date: Fri, 11 May 2001 10:28:59 +0100
+.endd
+The asterisked headers indicate that the envelope sender, ::From:: header, and
+::To:: header have been rewritten, the last one because routing expanded the
+unqualified domain \*foundation*\.
+
+.
+.
+.
+.
+. ============================================================================
+.chapter Adding new drivers or lookup types
+.set runningfoot "adding drivers"
+.index adding drivers
+.index new drivers, adding
+.index drivers||adding new
+The following actions have to be taken in order to add a new router, transport,
+authenticator, or lookup type to Exim:
+.numberpars
+Choose a name for the driver or lookup type that does not conflict with any
+existing name; I will use `newdriver' in what follows.
+.nextp
+Add to \(src/EDITME)\ the line
+.display
+<<type>>@_NEWDRIVER=yes
+.endd
+where <<type>> is \\ROUTER\\, \\TRANSPORT\\, \\AUTH\\, or \\LOOKUP\\. If the
+code is not to be included in the binary by default, comment this line out. You
+should also add any relevant comments about the driver or lookup type.
+.nextp
+Add to \(src/config.h.defaults)\ the line
+.display
+@#define <<type>>@_NEWDRIVER
+.endd
+.nextp
+Edit \(src/drtables.c)\, adding conditional code to pull in the private header
+and create a table entry as is done for all the other drivers and lookup types.
+.nextp
+Edit \(Makefile)\ in the appropriate sub-directory (\(src/routers)\,
+\(src/transports)\, \(src/auths)\, or \(src/lookups)\); add a line for the new
+driver or lookup type and add it to the definition of OBJ.
+.nextp
+Create \(newdriver.h)\ and \(newdriver.c)\ in the appropriate sub-directory of
+\(src)\.
+.nextp
+Edit \(scripts/MakeLinks)\ and add commands to link the \(.h)\ and \(.c)\ files
+as for other drivers and lookups.
+.endp
+Then all you need to do is write the code! A good way to start is to make a
+proforma by copying an existing module of the same type, globally changing all
+occurrences of the name, and cutting out most of the code. Note that any
+options you create must be listed in alphabetical order, because the tables are
+searched using a binary chop procedure.
+
+There is a \(README)\ file in each of the sub-directories of \(src)\ describing
+the interface that is expected.
+
+.
+.
+.
+.
+. ============================================================================
+. Fudge for the index page number. We want it to be on a right-hand page.
+.
+.set indexpage ~~sys.pagenumber + 1
+.if even ~~indexpage
+.set indexpage ~~indexpage + 1
+.fi
+.if ~~sgcal
+.%index Index$e~~indexpage--
+.fi
+.
+.
+. End of Exim specification
git://git.exim.org / exim.git / blobdiff