-. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.18 2007/05/15 19:04:56 magnus Exp $
+. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.88 2010/06/14 18:51:09 pdp Exp $
.
. /////////////////////////////////////////////////////////////////////////////
. This is the primary source of the Exim Manual. It is an xfpt document that is
. converted into DocBook XML for subsequent conversion into printing and online
. formats. The markup used herein is "standard" xfpt markup, with some extras.
. The markup is summarized in a file called Markup.txt.
+.
+. WARNING: When you use the .new macro, make sure it appears *before* any
+. adjacent index items; otherwise you get an empty "paragraph" which causes
+. unwanted vertical space.
. /////////////////////////////////////////////////////////////////////////////
.include stdflags
foot_right_recto="&chaptertitle; (&chapternumber;)"
foot_right_verso="&chaptertitle; (&chapternumber;)"
toc_chapter_blanks="yes,yes"
- table_warn_soft_overflow="no"
+ table_warn_overflow="overprint"
?>
.literal off
. the <bookinfo> element must also be updated for each new edition.
. /////////////////////////////////////////////////////////////////////////////
-.set previousversion "4.66"
-.set version "4.67"
+.set previousversion "4.72"
+.set version "4.73"
.set ACL "access control lists (ACLs)"
.set I " "
<bookinfo>
<title>Specification of the Exim Mail Transfer Agent</title>
<titleabbrev>The Exim MTA</titleabbrev>
-<date>10 April 2007</date>
-<author><firstname>Philip</firstname><surname>Hazel</surname></author>
-<authorinitials>PH</authorinitials>
-<affiliation><orgname>University of Cambridge Computing Service</orgname></affiliation>
-<address>New Museums Site, Pembroke Street, Cambridge CB2 3QH, England</address>
+<date>29 May 2010</date>
+<author><firstname>Exim</firstname><surname>Maintainers</surname></author>
+<authorinitials>EM</authorinitials>
<revhistory><revision>
- <revnumber>4.67</revnumber>
- <date>10 April 2007</date>
- <authorinitials>PH</authorinitials>
+ <revnumber>4.73</revnumber>
+ <date>19 Nov 2010</date>
+ <authorinitials>EM</authorinitials>
</revision></revhistory>
-<copyright><year>2007</year><holder>University of Cambridge</holder></copyright>
+<copyright><year>2009</year><holder>University of Cambridge</holder></copyright>
</bookinfo>
.literal off
</indexterm>
<indexterm role="concept">
<primary>maximum</primary>
- <see><emphasis>limit</emphasis></see>
+ <seealso><emphasis>limit</emphasis></seealso>
</indexterm>
<indexterm role="concept">
<primary>monitor</primary>
.section "Exim documentation" "SECID1"
+. Keep this example change bar when updating the documentation!
.new
.cindex "documentation"
This edition of the Exim specification applies to version &version; of Exim.
.cindex "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 &'The Exim
-SMTP Mail Server'&, published by UIT Cambridge
+SMTP Mail Server'& (second edition, 2007), published by UIT Cambridge
(&url(http://www.uit.co.uk/exim-book/)).
This book also contains a chapter that gives a general introduction to SMTP and
.row &_exim.8_& "a man page of Exim's command line options"
.row &_experimental.txt_& "documentation of experimental features"
.row &_filter.txt_& "specification of the filter language"
-.row &_pcrepattern.txt_& "specification of PCRE regular expressions"
-.row &_pcretest.txt_& "specification of the PCRE testing program"
.row &_Exim3.upgrade_& "upgrade notes from release 2 to release 3"
.row &_Exim4.upgrade_& "upgrade notes from release 3 to release 4"
.endtable
.cindex "wiki"
.cindex "FAQ"
-.new
As well as Exim distribution tar files, the Exim web site contains a number of
differently formatted versions of the documentation. A recent addition to the
-online information is the Exim wiki (&url(http://www.exim.org/eximwiki/)),
+online information is the Exim wiki (&url(http://wiki.exim.org)),
which contains what used to be a separate FAQ, as well as various other
examples, tips, and know-how that have been contributed by Exim users.
.cindex Bugzilla
-An Exim Bugzilla exists at &url(http://www.exim.org/bugzilla/). You can use
+An Exim Bugzilla exists at &url(http://bugs.exim.org). You can use
this to report bugs, and also to add items to the wish list. Please search
first to check that you are not duplicating a previous entry.
-.wen
.section "Mailing lists" "SECID3"
.cindex "mailing lists" "for Exim users"
-.new
The following Exim mailing lists exist:
.table2 140pt
.row &'exim-announce@exim.org'& "Moderated, low volume announcements list"
.row &'exim-future@exim.org'& "Discussion of long-term development"
.endtable
-.wen
You can subscribe to these lists, change your existing subscriptions, and view
or search the archives via the mailing lists link on the Exim home page.
.section "Exim training" "SECID4"
.cindex "training courses"
-From time to time (approximately annually at the time of writing), training
-courses are run by the author of Exim in Cambridge, UK. Details of any
-forthcoming courses can be found on the web site
-&url(http://www-tus.csx.cam.ac.uk/courses/exim/).
-
+Training courses in Cambridge (UK) used to be run annually by the author of
+Exim, before he retired. At the time of writing, there are no plans to run
+further Exim courses in Cambridge. However, if that changes, relevant
+information will be posted at &url(http://www-tus.csx.cam.ac.uk/courses/exim/).
.section "Bug reports" "SECID5"
.cindex "bug reports"
.cindex "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 &'exim-dev'& mailing list and have it discussed.
+Reports of obvious bugs can be emailed to &'bugs@exim.org'& or reported
+via the Bugzilla (&url(http://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 &'exim-dev'& mailing list and have it discussed.
.cindex "distribution" "signing details"
.cindex "distribution" "public key"
.cindex "public key for signed distribution"
-The distributions are currently signed with Philip Hazel's GPG key. The
+The distributions are currently signed with Nigel Metheringham's GPG key. The
corresponding public key is available from a number of keyservers, and there is
-also a copy in the file &_Public-Key_&. The signatures for the tar bundles are
+also a copy in the file &_nigel-pubkey.asc_&. The signatures for the tar bundles are
in:
.display
-&_exim-n.nn.tar.gz.sig_&
-&_exim-n.nn.tar.bz2.sig_&
+&_exim-n.nn.tar.gz.asc_&
+&_exim-n.nn.tar.bz2.asc_&
.endd
For each released version, the log of changes is made separately available in a
separate file in the directory &_ChangeLogs_& so that it is possible to
A number of pieces of external code are included in the Exim distribution.
.ilist
-Regular expressions are supported in the main Exim program and in the Exim
-monitor using the freely-distributable PCRE library, copyright ©
-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 of the library from
+Regular expressions are supported in the main Exim program and in the
+Exim monitor using the freely-distributable PCRE library, copyright
+© University of Cambridge. The source to PCRE is no longer shipped with
+Exim, so you will need to use the version of PCRE shipped with your system,
+or obtain and install the full version of the library from
&url(ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre).
.next
.cindex "cdb" "acknowledgment"
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
&url(http://www.pobox.com/~djb/cdb.html). This implementation borrows
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,
-
.cindex "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
overridden if necessary.
+.section "PCRE library" "SECTpcre"
+.cindex "PCRE library"
+Exim no longer has an embedded PCRE library as the vast majority of
+modern systems include PCRE as a system library, although you may need
+to install the PCRE or PCRE development package for your operating
+system. If your system has a normal PCRE installation the Exim build
+process will need no further configuration. If the library or the
+headers are in an unusual location you will need to set the PCRE_LIBS
+and INCLUDE directives appropriately. If your operating system has no
+PCRE support then you will need to obtain and build the current PCRE
+from &url(ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre/).
+
.section "DBM libraries" "SECTdb"
.cindex "DBM libraries" "discussion of"
.cindex "hints database" "DBM files used for"
.section "Use of tcpwrappers" "SECID27"
+.new
.cindex "tcpwrappers, building Exim to support"
.cindex "USE_TCP_WRAPPERS"
+.cindex "TCP_WRAPPERS_DAEMON_NAME"
+.cindex "tcp_wrappers_daemon_name"
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
CFLAGS=-O -I/usr/local/include
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
+in &_Local/Makefile_&. The daemon name to use in the &'tcpwrappers'& control
+files is &"exim"&. For example, the line
.code
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
+All other connections are denied. The daemon name used by &'tcpwrappers'&
+can be changed at build time by setting TCP_WRAPPERS_DAEMON_NAME in
+in &_Local/Makefile_&, or by setting tcp_wrappers_daemon_name in the
+configure file. Consult the &'tcpwrappers'& documentation for
further details.
-
+.wen
.section "Including support for IPv6" "SECID28"
+.section "Dynamically loaded lookup module support" "SECTdynamicmodules"
+.cindex "lookup modules"
+.cindex "dynamic modules"
+.cindex ".so building"
+On some platforms, Exim supports not compiling all lookup types directly into
+the main binary, instead putting some into external modules which can be loaded
+on demand.
+This permits packagers to build Exim with support for lookups with extensive
+library dependencies without requiring all users to install all of those
+dependencies.
+Most, but not all, lookup types can be built this way.
+
+Set &`LOOKUP_MODULE_DIR`& to the directory into which the modules will be
+installed; Exim will only load modules from that directory, as a security
+measure. You will need to set &`CFLAGS_DYNAMIC`& if not already defined
+for your OS; see &_OS/Makefile-Linux_& for an example.
+Some other requirements for adjusting &`EXTRALIBS`& may also be necessary,
+see &_src/EDITME_& for details.
+
+Then, for each module to be loaded dynamically, define the relevant
+&`LOOKUP_`&<&'lookup_type'&> flags to have the value "2" instead of "yes".
+For example, this will build in lsearch but load sqlite and mysql support
+on demand:
+.code
+LOOKUP_LSEARCH=yes
+LOOKUP_SQLITE=2
+LOOKUP_MYSQL=2
+.endd
+
+
.section "The building process" "SECID29"
.cindex "build directory"
Once &_Local/Makefile_& (and &_Local/eximon.conf_&, if required) have been
.cindex "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_&
+&'convert4r4'&. You will probably run this only once if you are
+upgrading from Exim 3. 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.
The same output is generated if the Exim binary is called with no options and
no arguments.
+.new
+.vitem &%--version%&
+.oindex "&%--version%&"
+This option is an alias for &%-bV%& and causes version information to be
+displayed.
+.wen
+
.vitem &%-B%&<&'type'&>
.oindex "&%-B%&"
.cindex "8-bit characters"
output just states whether a given recipient address from a given host is
acceptable or not. See section &<<SECTcheckaccess>>&.
-.new
Features such as authentication and encryption, where the client input is not
plain text, cannot easily be tested with &%-bh%&. Instead, you should use a
specialized SMTP test program such as
&url(http://jetmore.org/john/code/#swaks,swaks).
-.wen
.vitem &%-bhc%&&~<&'IP&~address'&>
.oindex "&%-bhc%&"
.vitem &%-bP%&
.oindex "&%-bP%&"
-.cindex "configuration options, extracting"
+.cindex "configuration options" "extracting"
.cindex "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
.code
exim -bP qualify_domain hold_domains
.endd
+.cindex "hiding configuration option values"
+.cindex "configuration options" "hiding value of"
+.cindex "options" "hiding value of"
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:
.cindex "options" "router &-- extracting"
.cindex "options" "transport &-- extracting"
+.cindex "options" "authenticator &-- 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:
settings can be obtained by using &%routers%&, &%transports%&, or
&%authenticators%&.
+.cindex "options" "macro &-- extracting"
+If invoked by an admin user, then &%macro%&, &%macro_list%& and &%macros%&
+are available, similarly to the drivers. Because macros are sometimes used
+for storing passwords, this option is restricted.
+The output format is one item per line.
.vitem &%-bp%&
.oindex "&%-bp%&"
Exim behaves in exactly the same way as it does when receiving a message via
the listening daemon.
+.new
+.vitem &%-bmalware%&&~<&'filename'&>
+.oindex "&%-bmalware%&"
+.cindex "testing", "malware"
+.cindex "malware scan test"
+This debugging option causes Exim to scan the given file,
+using the malware scanning framework. The option of &%av_scanner%& influences
+this option, so if &%av_scanner%&'s value is dependent upon an expansion then
+the expansion should have defaults which apply to this invocation. ACLs are
+not invoked, so if &%av_scanner%& references an ACL variable then that variable
+will never be populated and &%-bmalware%& will fail.
+
+Exim will have changed working directory before resolving the filename, so
+using fully qualified pathnames is advisable. Exim will be running as the Exim
+user when it tries to open the file, rather than as the invoking user.
+This option requires admin privileges.
+
+The &%-bmalware%& option will not be extended to be more generally useful,
+there are better tools for file-scanning. This option exists to help
+administrators verify their Exim and AV scanner configuration.
+.wen
+
.vitem &%-bt%&
.oindex "&%-bt%&"
.cindex "testing" "addresses"
.cindex "address" "testing"
This option runs Exim in address testing mode, in which each argument is taken
-as a &new(recipient) address to be tested for deliverability. The results are
+as a recipient 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.
.cindex "version number of Exim"
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
+It also lists the DBM library that 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.
.cindex "verifying address" "using &%-bv%&"
.cindex "address" "verification"
This option runs Exim in address verification mode, in which each argument is
-taken as a &new(recipient) address to be verified by the routers. (This does
+taken as a recipient address to be verified by the routers. (This does
not involve any verification callouts). 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, possibly
than a recipient address. This affects any rewriting and qualification that
might happen.
+.new
.vitem &%-C%&&~<&'filelist'&>
.oindex "&%-C%&"
.cindex "configuration file" "alternate"
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.
-
-That is, the Exim user is no longer privileged in this regard. This build-time
-option is not set by default in the Exim source distribution tarbundle.
-However, if you are using a &"packaged"& version of Exim (source or binary),
-the packagers might have enabled it.
-
-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-executes 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%&).
+When this option is used by a caller other than root, 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 a TRUSTED_CONFIG_LIST file is defined in &_Local/Makefile_&, that
+file contains a list of full pathnames, one per line, for configuration files
+which are trusted. Root privilege is retained for any configuration file so
+listed, as long as the caller is the Exim user (or the user specified in the
+CONFIGURE_OWNER option, if any), and as long as the configuration file is
+not writeable by inappropriate users or groups.
+
+Leaving TRUSTED_CONFIG_LIST unset precludes 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-executes 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
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.
+.wen
+.new
.vitem &%-D%&<&'macro'&>=<&'value'&>
.oindex "&%-D%&"
.cindex "macro" "setting on command line"
If DISABLE_D_OPTION is defined in &_Local/Makefile_&, the use of &%-D%& is
completely disabled, and its use causes an immediate error exit.
+If WHITELIST_D_MACROS is defined in &_Local/Makefile_& then it should be a
+colon-separated list of macros which are considered safe and, if &%-D%& only
+supplies macros from this list, and the values are acceptable, then Exim will
+not give up root privilege if the caller is root, the Exim run-time user, or
+the CONFIGURE_OWNER, if set. This is a transition mechanism and is expected
+to be removed in the future. Acceptable values for the macros satisfy the
+regexp: &`^[A-Za-z0-9_/.-]*$`&
+
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
exim '-D ABC = something' ...
.endd
&%-D%& may be repeated up to 10 times on a command line.
+.wen
.vitem &%-d%&<&'debug&~options'&>
.oindex "&%-d%&"
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.
+.vitem &%-Mvc%&&~<&'message&~id'&>
+.oindex "&%-Mvc%&"
+.cindex "message" "listing in RFC 2822 format"
+.cindex "listing" "message in RFC 2822 format"
+This option causes a copy of the complete message (header lines plus body) to
+be written to the standard output in RFC 2822 format. This option can be used
+only by an admin user.
+
.vitem &%-Mvh%&&~<&'message&~id'&>
.oindex "&%-Mvh%&"
.cindex "listing" "message headers"
give a colon-separated list of file names, in which case Exim uses the first
existing file in the list.
+.new
.cindex "EXIM_USER"
.cindex "EXIM_GROUP"
.cindex "CONFIGURE_OWNER"
.cindex "configuration file" "ownership"
.cindex "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, or by the user that is
specified at compile time by the CONFIGURE_OWNER option (if set). 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 or by the
+configuration file must not be world-writeable, or group-writeable unless its
+group is the root group or the one specified at compile time by the
CONFIGURE_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.
+easy way to run commands as root. If you specify a user or group in the
+CONFIGURE_OWNER or CONFIGURE_GROUP options, then that user and/or any users
+who are members of that group will trivially be able to obtain root privileges.
+
+Up to Exim version 4.72, the run time configuration file was also permitted to
+be writeable by the Exim user and/or group. That has been changed in Exim 4.73
+since it offered a simple privilege escalation for any attacker who managed to
+compromise the Exim user account.
A default configuration file, which will work correctly in simple situations,
is provided in the file &_src/configure.default_&. If CONFIGURE_FILE
CONFIGURE_FILE is a list, no default is automatically installed. Chapter
&<<CHAPdefconfil>>& is a &"walk-through"& discussion of the default
configuration.
-
+.wen
.section "Using a different configuration file" "SECID40"
.cindex "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%&).
+&%-C%& is used, Exim gives up its root privilege, unless called by root (or
+unless the argument for &%-C%& is identical to the built-in value from
+CONFIGURE_FILE), or is listed in the TRUSTED_CONFIG_LIST file and the caller
+is the Exim user or the user specified in the CONFIGURE_OWNER setting. &%-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%&, if root privilege has been dropped.
+
+Even the Exim user is not trusted to specify an arbitrary configuration file
+with the &%-C%& option to be used with root privileges, unless that file is
+listed in the TRUSTED_CONFIG_LIST file. This 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
If DISABLE_D_OPTION is defined in &_Local/Makefile_&, the use of &%-D%& is
completely disabled, and its use causes an immediate error exit.
+.new
+The WHITELIST_D_MACROS option in &_Local/Makefile_& permits the binary builder
+to declare certain macro names trusted, such that root privilege will not
+necessarily be discarded.
+WHITELIST_D_MACROS defines a colon-separated list of macros which are
+considered safe and, if &%-D%& only supplies macros from this list, and the
+values are acceptable, then Exim will not give up root privilege if the caller
+is root, the Exim run-time user, or the CONFIGURE_OWNER, if set. This is a
+transition mechanism and is expected to be removed in the future. Acceptable
+values for the macros satisfy the regexp: &`^[A-Za-z0-9_/.-]*$`&
+.wen
+
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
optional parts are:
.ilist
-&'ACL'&: Access control lists for controlling incoming SMTP mail.
+&'ACL'&: Access control lists for controlling incoming SMTP mail (see chapter
+&<<CHAPACL>>&).
.next
.cindex "AUTH" "configuration"
&'authenticators'&: Configuration settings for the authenticator drivers. These
are concerned with the SMTP AUTH command (see chapter &<<CHAPSMTPAUTH>>&).
.next
&'routers'&: Configuration settings for the router drivers. Routers process
-addresses and determine how the message is to be delivered.
+addresses and determine how the message is to be delivered (see chapters
+&<<CHAProutergeneric>>&&--&<<CHAPredirect>>&).
.next
&'transports'&: Configuration settings for the transport drivers. Transports
-define mechanisms for copying messages to destinations.
+define mechanisms for copying messages to destinations (see chapters
+&<<CHAPtransportgeneric>>&&--&<<CHAPsmtptrans>>&).
.next
-&'retry'&: Retry rules, for use when a message cannot be immediately delivered.
+&'retry'&: Retry rules, for use when a message cannot be delivered immediately.
+If there is no retry section, or if it is empty (that is, no retry rules are
+defined), Exim will not retry deliveries. In this situation, temporary errors
+are treated the same as permanent errors. Retry rules are discussed in chapter
+&<<CHAPretry>>&.
.next
&'rewrite'&: Global address rewriting rules, for use when a message arrives and
-when new addresses are generated during delivery.
+when new addresses are generated during delivery. Rewriting is discussed in
+chapter &<<CHAPrewrite>>&.
.next
&'local_scan'&: Private options for the &[local_scan()]& function. If you
want to use this feature, you must set
.code
LOCAL_SCAN_HAS_OPTIONS=yes
.endd
-in &_Local/Makefile_& before building Exim. Full details of the
-&[local_scan()]& facility are given in chapter &<<CHAPlocalscan>>&.
+in &_Local/Makefile_& before building Exim. Details of the &[local_scan()]&
+facility are given in chapter &<<CHAPlocalscan>>&.
.endlist
.cindex "configuration file" "leading white space in"
strings such as SQL statements are defined separately as macros, for example:
.code
ALIAS_QUERY = select mailbox from user where \
- login=${quote_mysql:$local_part};
+ login='${quote_mysql:$local_part}';
.endd
This can then be used in a &(redirect)& router setting like this:
.code
.code
qualify_domain = mydomain.example.com
.endd
+.cindex "hiding configuration option values"
+.cindex "configuration options" "hiding value of"
+.cindex "options" "hiding value of"
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
.section "Integer values" "SECID48"
.cindex "integer configuration values"
.cindex "format" "integer"
-.new
If an option's type is given as &"integer"&, the value can be given in decimal,
hexadecimal, or octal. If it starts with a digit greater than zero, a decimal
number is assumed. Otherwise, it is treated as an octal number unless it starts
with the characters &"0x"&, in which case the remainder is interpreted as a
hexadecimal number.
-.wen
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
.section "Octal integer values" "SECID49"
.cindex "integer format"
.cindex "format" "octal integer"
-.new
If an option's type is given as &"octal integer"&, its value is always
interpreted as an octal number, whether or not it starts with the digit zero.
Such options are always output in octal.
-.wen
.section "Fixed point numbers" "SECID50"
.cindex "fixed point configuration values"
.cindex "format" "fixed point"
-.new
If an option's type is given as &"fixed-point"&, its value must be a decimal
integer, optionally followed by a decimal point and up to three further digits.
-.wen
.section "String values" "SECTstrings"
.cindex "string" "format of configuration values"
.cindex "format" "string"
-.new
If an option's type is specified as &"string"&, the value can be specified with
or without double-quotes. If it does not start with a double-quote, the value
consists of the remainder of the line plus any continuation lines, starting at
Exim removes comment lines (those beginning with #) at an early stage, they can
appear in the middle of a multi-line string. The following two settings are
therefore equivalent:
-.wen
.code
trusted_users = uucp:mail
trusted_users = uucp:\
colon in the example above is necessary. If it were not there, the list would
be interpreted as the two items 127.0.0.1:: and 1.
-.new
.section "Changing list separators" "SECID53"
.cindex "list separator" "changing"
.cindex "IPv6" "addresses in lists"
-.wen
Doubling colons in IPv6 addresses 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
&%log_file_path%&. It is recommended that the use of non-colon separators be
confined to circumstances where they really are needed.
-.new
.cindex "list separator" "newline as"
-.cindex "newline as list separator"
+.cindex "newline" "as list separator"
It is also possible to use newline and other control characters (those with
code values less than 32, plus DEL) as separators in lists. Such separators
must be provided literally at the time the list is processed. For options that
doubling, it is not possible to include a control character as data when it is
set as the separator. Two such characters in succession are interpreted as
enclosing an empty list item.
-.wen
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 temporary failure, it is bounced.
+If the retry section is removed from the configuration, or is empty (that is,
+if no retry rules are defined), Exim will not retry deliveries. This turns
+temporary errors into permanent errors.
.section "Rewriting configuration" "SECID58"
To make the authenticators work, you can use a string expansion
expression like one of the examples in &<<CHAPplaintext>>&.
+Beware that the sequence of the parameters to PLAIN and LOGIN differ; the
+usercode and password are in different positions. &<<CHAPplaintext>>&
+covers both.
+
.ecindex IIDconfiwal
O'Reilly (see &url(http://www.oreilly.com/catalog/regex2/)).
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. 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.
+are supported by PCRE is included in the PCRE distribution, and 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.
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
-.section "Testing regular expressions" "SECID59"
-.cindex "testing" "regular expressions"
-.cindex "regular expressions" "testing"
-.cindex "&'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> `&&*&`/^([@]+)@.+\.(ac|edu)\.(?!kr)[a-z]{2}$/`&*&
-&`data> `&&*&`x@y.ac.uk`&*&
-&` 0: x@y.ac.uk`&
-&` 1: x`&
-&` 2: ac`&
-&`data> `&&*&`x@y.ac.kr`&*&
-&`No match`&
-&`data> `&&*&`x@y.edu.com`&*&
-&`No match`&
-&`data> `&&*&`x@y.edu.co`&*&
-&` 0: x@y.edu.co`&
-&` 1: x`&
-&` 2: edu`&
-.endd
-Input typed by the user is shown in bold face. 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 &$2$&.
-
-
-
-
-
-
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
.next
.cindex "lookup" "dsearch"
.cindex "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
+&(dsearch)&: The given file must be a directory; this is searched for an entry
+whose name is the key by calling the &[lstat()]& function. The key may not
+contain any forward slash characters. If &[lstat()]& succeeds, the result of
+the lookup is the name of the entry, which may be a file, directory,
+symbolic link, or any other kind of directory entry. An example of how this
+lookup can be used to support virtual domains is given in section
&<<SECTvirtualdomains>>&.
.next
.cindex "lookup" "iplsearch"
being interpreted as a key terminator. For example:
.code
1.2.3.4: data for 1.2.3.4
-192.168.0.0/16 data for 192.168.0.0/16
+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
.next
.cindex "whoson lookup type"
.cindex "lookup" "whoson"
-.new
&(whoson)&: &'Whoson'& (&url(http://whoson.sourceforge.net)) is a protocol that
allows a server to check whether a particular (dynamically allocated) IP
address is currently allocated to a known (trusted) user and, optionally, to
the authenticated user, which is stored in the variable &$value$&. However, in
this example, the data in &$value$& is not used; the result of the lookup is
one of the fixed strings &"yes"& or &"no"&.
-.wen
.endlist
It is permitted to specify a space as the separator character. Further
white space is ignored.
+.cindex "TXT record" "in &(dnsdb)& lookup"
+For TXT records with multiple items of data, only the first item is returned,
+unless a separator for them is specified using a comma after the separator
+character followed immediately by the TXT record item separator. To concatenate
+items without a separator, use a semicolon instead.
+.code
+${lookup dnsdb{>\n,: txt=a.b.example}}
+${lookup dnsdb{>\n; txt=a.b.example}}
+.endd
+It is permitted to specify a space as the separator character. Further
+white space is ignored.
+
.section "Pseudo dnsdb record types" "SECID66"
.cindex "MX record" "in &(dnsdb)& lookup"
By default, both the preference value and the host name are returned for
.section "SQL lookups" "SECTsql"
.cindex "SQL lookup types"
+.cindex "MySQL" "lookup type"
+.cindex "PostgreSQL lookup type"
+.cindex "lookup" "MySQL"
+.cindex "lookup" "PostgreSQL"
+.cindex "Oracle" "lookup type"
+.cindex "lookup" "Oracle"
+.cindex "InterBase lookup type"
+.cindex "lookup" "InterBase"
Exim can support lookups in InterBase, MySQL, Oracle, PostgreSQL, and SQLite
databases. Queries for these databases contain SQL statements, so an example
might be
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:
+information.
+(For MySQL and PostgreSQL only, the global option need not be set if all
+queries contain their own server information &-- see section
+&<<SECTspeserque>>&.) 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:
.code
hide oracle_servers = oracle.plc.example//userx/abcdwxyz
.endd
.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.
+query, these parameter groups are tried in order until a connection is made and
+a query is successfully processed. The result of a query may be that no data is
+found, but that is still a successful query. In other words, the list of
+servers provides a backup facility, not a list of different places to look.
The &%quote_mysql%&, &%quote_pgsql%&, and &%quote_oracle%& expansion operators
convert newline, tab, carriage return, and backspace to \n, \t, \r, and \b
for MySQL because these escapes are not recognized in contexts where these
characters are not special.
+.section "Specifying the server in the query" "SECTspeserque"
+For MySQL and PostgreSQL lookups (but not currently for Oracle and InterBase),
+it is possible to specify a list of servers with an individual query. This is
+done by starting the query with
+.display
+&`servers=`&&'server1:server2:server3:...'&&`;`&
+.endd
+Each item in the list may take one of two forms:
+.olist
+If it contains no slashes it is assumed to be just a host name. The appropriate
+global option (&%mysql_servers%& or &%pgsql_servers%&) is searched for a host
+of the same name, and the remaining parameters (database, user, password) are
+taken from there.
+.next
+If it contains any slashes, it is taken as a complete parameter set.
+.endlist
+The list of servers is used in exactly the same way as the global list.
+Once a connection to a server has happened and a query has been
+successfully executed, processing of the lookup ceases.
+
+This feature is intended for use in master/slave situations where updates
+are occurring and you want to update the master rather than a slave. If the
+master is in the list as a backup for reading, you might have a global setting
+like this:
+.code
+mysql_servers = slave1/db/name/pw:\
+ slave2/db/name/pw:\
+ master/db/name/pw
+.endd
+In an updating lookup, you could then write:
+.code
+${lookup mysql{servers=master; UPDATE ...} }
+.endd
+That query would then be sent only to the master server. If, on the other hand,
+the master is not to be used for reading, and so is not present in the global
+option, you can still update it by a query of this form:
+.code
+${lookup pgsql{servers=master/db/name/pw; UPDATE ...} }
+.endd
+
.section "Special MySQL features" "SECID73"
For MySQL, an empty host name or the use of &"localhost"& in &%mysql_servers%&
.cindex "@[] in a domain list"
.cindex "domain list" "matching local IP interfaces"
.cindex "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.
+If a pattern consists of the string &`@[]`& it matches an IP address enclosed
+in square brackets (as in an email address that contains a domain literal), but
+only if that IP address is recognized as local for email routing purposes. The
+&%local_interfaces%& and &%extra_local_interfaces%& options can be used to
+control which of a host's several IP addresses are treated as local.
In today's Internet, the use of domain literals is controversial.
.next
.cindex "@mx_any"
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>>&.
+Email domains are case-independent, so this regular expression match is by
+default case-independent, but you can make it case-dependent by starting it
+with &`(?-i)`&. 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
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
+&"192.168.34.0/24"&.
+
+When an IPv6 address is converted to a string, dots are normally used instead
+of colons, so that keys in &(lsearch)& files need not contain colons (which
+terminate &(lsearch)& keys). This was implemented some time before the ability
+to quote keys was made available in &(lsearch)& files. However, the more
+recently implemented &(iplsearch)& files do require colons in IPv6 keys
+(notated using the quoting facility) so as to distinguish them from IPv4 keys.
+For this reason, when the lookup type is &(iplsearch)&, IPv6 addresses are
+converted using colons and not dots. In all cases, full, unabbreviated IPv6
addresses are always used.
+Ideally, it would be nice to tidy up this anomalous situation by changing to
+colons in all cases, given that quoting is now available for &(lsearch)&.
+However, this would be an incompatible change that might break some existing
+configurations.
+
&*Warning*&: Specifying &%net32-%& (for an IPv4 address) or &%net128-%& (for an
IPv6 address) is not the same as specifying just &%net-%& without a number. In
the former case the key strings include the mask value, whereas in the latter
.cindex "regular expressions" "in host list"
.cindex "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,
+matched against the host name. Host names are case-independent, so this regular
+expression match is by default case-independent, but you can make it
+case-dependent by starting it with &`(?-i)`&. References to descriptions of the
+syntax of regular expressions are given in chapter &<<CHAPregexp>>&. For
+example,
.code
^(a|b)\.c\.d$
.endd
.section "Behaviour when an IP address or name cannot be found" "SECTbehipnot"
-.cindex "host" "lookup failures"
+.cindex "host" "lookup failures, permanent"
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.
+&*Note*&: This section applies to permanent lookup failures. It does &'not'&
+apply to temporary DNS errors, whose handling is described in the next section.
+
.cindex "&`+include_unknown`&"
.cindex "&`+ignore_unknown`&"
By default, Exim behaves as if the host does not match the list. This may not
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 (except when
-&%dns_again_means_nonexist%& converts them into permanent errors).
+
+.section "Temporary DNS errors when looking up host information" &&&
+ "SECTtemdnserr"
+.cindex "host" "lookup failures, temporary"
+.cindex "&`+include_defer`&"
+.cindex "&`+ignore_defer`&"
+A temporary DNS lookup failure normally causes a defer action (except when
+&%dns_again_means_nonexist%& converts it into a permanent error). However,
+host lists can include &`+ignore_defer`& and &`+include_defer`&, analagous to
+&`+ignore_unknown`& and &`+include_unknown`&, as described in the previous
+section. These options should be used with care, probably only in non-critical
+host lists such as whitelists.
.section "Host list patterns for single-key lookups by host name" &&&
"SECThoslispatnamsk"
-.cindex "host" "lookup failures"
.cindex "unknown host name"
.cindex "host list" "matching host name"
If a pattern is of the form
one argument, because it reduces the number of braces and therefore makes the
string easier to understand.
+.vitem &*$bheader_*&<&'header&~name'&>&*:*&&~or&~&*$bh_*&<&'header&~name'&>&*:*&
+This item inserts &"basic"& header lines. It is described with the &%header%&
+expansion item below.
+
.vitem "&*${dlfunc{*&<&'file'&>&*}{*&<&'function'&>&*}{*&<&'arg'&>&*}&&&
{*&<&'arg'&>&*}...}*&"
.cindex &%dlfunc%&
empty (for example, the fifth field above).
-.new
.vitem &*${filter{*&<&'string'&>&*}{*&<&'condition'&>&*}}*&
.cindex "list" "selecting by condition"
.cindex "expansion" "selecting from list by condition"
.endd
yields &`a:c`&. At the end of the expansion, the value of &$item$& is restored
to what it was before. See also the &*map*& and &*reduce*& expansion items.
-.wen
.vitem &*${hash{*&<&'string1'&>&*}{*&<&'string2'&>&*}{*&<&'string3'&>&*}}*&
.endd
.vitem "&*$header_*&<&'header&~name'&>&*:*&&~or&~&&&
- &*$h_*&<&'header&~name'&>&*:*&"
-See &*$rheader*& below.
-
-.vitem "&*$bheader_*&<&'header&~name'&>&*:*&&~or&~&&&
- &*$bh_*&<&'header&~name'&>&*:*&"
-See &*$rheader*& below.
-
-.vitem "&*$rheader_*&<&'header&~name'&>&*:*&&~or&~&&&
+ &*$h_*&<&'header&~name'&>&*:*&" &&&
+ "&*$bheader_*&<&'header&~name'&>&*:*&&~or&~&&&
+ &*$bh_*&<&'header&~name'&>&*:*&" &&&
+ "&*$rheader_*&<&'header&~name'&>&*:*&&~or&~&&&
&*$rh_*&<&'header&~name'&>&*:*&"
.cindex "expansion" "header insertion"
.vindex "&$header_$&"
.endd
-.new
.vitem &*${map{*&<&'string1'&>&*}{*&<&'string2'&>&*}}*&
.cindex "expansion" "list creation"
.vindex "&$item$&"
expands to &`[a]:[b]:[c] (x)-(y)-(z)`&. At the end of the expansion, the
value of &$item$& is restored to what it was before. See also the &*filter*&
and &*reduce*& expansion items.
-.wen
.vitem &*${nhash{*&<&'string1'&>&*}{*&<&'string2'&>&*}{*&<&'string3'&>&*}}*&
.cindex "expansion" "numeric hash"
locks out the use of this expansion item in filter files.
-.new
.vitem &*${reduce{*&<&'string1'&>}{<&'string2'&>&*}{*&<&'string3'&>&*}}*&
.cindex "expansion" "reducing a list to a scalar"
.cindex "list" "reducing to a scalar"
At the end of a &*reduce*& expansion, the values of &$item$& and &$value$& are
restored to what they were before. See also the &*filter*& and &*map*&
expansion items.
-.wen
-.vitem &*$rheader_*&<&'header&~name'&>&*:&~or&~$rh_*&<&'header&~name'&>&*:*&
+.vitem &*$rheader_*&<&'header&~name'&>&*:*&&~or&~&*$rh_*&<&'header&~name'&>&*:*&
This item inserts &"raw"& header lines. It is described with the &%header%&
expansion item above.
not parse successfully, the result is empty.
-.new
.vitem &*${addresses:*&<&'string'&>&*}*&
.cindex "expansion" "RFC 2822 address handling"
.cindex "&%addresses%& expansion item"
expansion item, which extracts the working address from a single RFC2822
address. See the &*filter*&, &*map*&, and &*reduce*& items for ways of
processing lists.
-.wen
.vitem &*${base62:*&<&'digits'&>&*}*&
yields an unchanged string.
+.vitem &*${randint:*&<&'n'&>&*}*&
+.cindex "random number"
+This operator returns a somewhat random number which is less than the
+supplied number and is at least 0. The quality of this randomness depends
+on how Exim was built; the values are not suitable for keying material.
+If Exim is linked against OpenSSL then RAND_pseudo_bytes() is used.
+Otherwise, the implementation may be arc4random(), random() seeded by
+srandomdev() or srandom(), or a custom implementation even weaker than
+random().
+
+
+.new
+.vitem &*${reverse_ip:*&<&'ipaddr'&>&*}*&
+.cindex "expansion" "IP address"
+This operator reverses an IP address; for IPv4 addresses, the result is in
+dotted-quad decimal form, while for IPv6 addreses the result is in
+dotted-nibble hexadecimal form. In both cases, this is the "natural" form
+for DNS. For example,
+.code
+${reverse_ip:192.0.2.4} and ${reverse_ip:2001:0db8:c42:9:1:abcd:192.0.2.3}
+.endd
+returns
+.code
+4.2.0.192 and 3.0.2.0.0.0.0.c.d.c.b.a.1.0.0.0.9.0.0.0.2.4.c.0.8.b.d.0.1.0.0.2
+.endd
+.wen
+
+
.vitem &*${rfc2047:*&<&'string'&>&*}*&
.cindex "expansion" "RFC 2047"
.cindex "RFC 2047" "expansion operator"
characters.
-.new
.vitem &*${rfc2047d:*&<&'string'&>&*}*&
.cindex "expansion" "RFC 2047"
.cindex "RFC 2047" "decoding"
bytes are replaced by question marks. Characters are converted into the
character set defined by &%headers_charset%&. Overlong RFC 2047 &"words"& are
not recognized unless &%check_rfc2047_length%& is set false.
-.wen
+
+&*Note*&: If you use &%$header%&_&'xxx'&&*:*& (or &%$h%&_&'xxx'&&*:*&) to
+access a header line, RFC 2047 decoding is done automatically. You do not need
+to use this operator as well.
As a special case, the numerical value of an empty string is taken as
zero.
+
+.new
+.vitem &*bool&~{*&<&'string'&>&*}*&
+.cindex "expansion" "boolean parsing"
+.cindex "&%bool%& expansion condition"
+This condition turns a string holding a true or false representation into
+a boolean state. It parses &"true"&, &"false"&, &"yes"& and &"no"&
+(case-insensitively); also positive integer numbers map to true if non-zero,
+false if zero. Leading and trailing whitespace is ignored.
+All other string values will result in expansion failure.
+
+When combined with ACL variables, this expansion condition will let you
+make decisions in one place and act on those decisions in another place.
+For example:
+.code
+${if bool{$acl_m_privileged_sender} ...
+.endd
+.wen
+
+
+.vitem &*bool_lax&~{*&<&'string'&>&*}*&
+.cindex "expansion" "boolean parsing"
+.cindex "&%bool_lax%& expansion condition"
+Like &%bool%&, this condition turns a string into a boolean state. But
+where &%bool%& accepts a strict set of strings, &%bool_lax%& uses the same
+loose definition that the Router &%condition%& option uses. The empty string
+and the values &"false"&, &"no"& and &"0"& map to false, all others map to
+true. Leading and trailing whitespace is ignored.
+
+Note that where &"bool{00}"& is false, &"bool_lax{00}"& is true.
+
.vitem &*crypteq&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*&
.cindex "expansion" "encrypted comparison"
.cindex "encrypted strings, comparing"
attempt. It is false during any subsequent delivery attempts.
-.new
.vitem "&*forall{*&<&'a list'&>&*}{*&<&'a condition'&>&*}*&" &&&
"&*forany{*&<&'a list'&>&*}{*&<&'a condition'&>&*}*&"
.cindex "list" "iterative conditions"
.endd
The value of &$item$& is saved and restored while &*forany*& or &*forall*& is
being processed, to enable these expansion items to be nested.
-.wen
.vitem &*ge&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*& &&&
.cindex "&%isip6%& expansion condition"
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
+&%isip4%& and &%isip6%& test specifically for IPv4 or IPv6 addresses.
+
+For an IPv4 address, the test is for four dot-separated components, each of
+which consists of from one to three digits. For an IPv6 address, up to eight
+colon-separated components are permitted, each containing from one to four
+hexadecimal digits. There may be fewer than eight components if an empty
+component (adjacent colons) is present. Only one empty component is permitted.
+
+&*Note*&: The checks are just on the form of the address; actual numerical
+values are not considered. Thus, for example, 999.999.999.999 passes the IPv4
+check. The main use of these tests is to distinguish between IP addresses and
+host names, or between IPv4 and IPv6 addresses. For example, you could use
.code
${if isip4{$sender_host_address}...
.endd
-to test which version of IP an incoming SMTP connection is using.
-
+to test which IP version an incoming SMTP connection is using.
.vitem &*ldapauth&~{*&<&'ldap&~query'&>&*}*&
.cindex "LDAP" "use for authentication"
.next
The item @[] matches any of the local host's interface addresses.
.next
-.new
Single-key lookups are assumed to be like &"net-"& style lookups in host lists,
even if &`net-`& is not specified. There is never any attempt to turn the IP
address into a host name. The most common type of linear search for
.code
${lookup{${mask:$sender_host_address/24}}dbm{/a/file}...
.endd
-.wen
.endlist ilist
Consult section &<<SECThoslispatip>>& for further details of these patterns.
.code
server_condition = ${if pwcheck{$auth1:$auth2}}
.endd
+Again, for a PLAIN authenticator configuration, this would be:
+.code
+server_condition = ${if pwcheck{$auth2:$auth3}}
+.endd
.vitem &*queue_running*&
.cindex "queue runner" "detecting when delivering from"
.cindex "expansion" "queue runner test"
.vlist
.vitem "&$0$&, &$1$&, etc"
.cindex "numerical variables (&$1$& &$2$& etc)"
-.new
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.
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.
-.wen
-.new
.vitem "&$acl_c...$&"
Values can be placed in these variables by the &%set%& modifier in an ACL. They
can be given any name that starts with &$acl_c$& and is at least six characters
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.
-.wen
.vitem &$acl_verify_message$&
.vindex "&$acl_verify_message$&"
content-scanning extension and the obsolete &%demime%& condition. For details,
see section &<<SECTdemimecond>>&.
-
-.vitem &$dnslist_domain$&
-.cindex "black list (DNS)"
+.vitem &$dnslist_domain$& &&&
+ &$dnslist_matched$& &&&
+ &$dnslist_text$& &&&
+ &$dnslist_value$&
.vindex "&$dnslist_domain$&"
-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.
-
-.vitem &$dnslist_text$&
+.vindex "&$dnslist_matched$&"
.vindex "&$dnslist_text$&"
-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.
-
-.vitem &$dnslist_value$&
.vindex "&$dnslist_value$&"
-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.
+.cindex "black list (DNS)"
+When a DNS (black) list lookup succeeds, these variables are set to contain
+the following data from the lookup: the list's domain name, the key that was
+looked up, the contents of any associated TXT record, and the value from the
+main A record. See section &<<SECID204>>& for more details.
.vitem &$domain$&
.vindex "&$domain$&"
.vindex "&$interface_port$&"
This is an obsolete name for &$received_port$&.
-.new
.vitem &$item$&
.vindex "&$item$&"
This variable is used during the expansion of &*forall*& and &*forany*&
-conditions (see section &<<SECTexpcond>>&), and &*filter*&, &*man*&, and
+conditions (see section &<<SECTexpcond>>&), and &*filter*&, &*map*&, and
&*reduce*& items (see section &<<SECTexpcond>>&). In other circumstances, it is
empty.
-.wen
.vitem &$ldap_dn$&
.vindex "&$ldap_dn$&"
.vitem &$load_average$&
.vindex "&$load_average$&"
-This variable contains the system load average, multiplied by 1000 to that it
+This variable contains the system load average, multiplied by 1000 so 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.
content-scanning extension. It is set to the name of the virus that was found
when the ACL &%malware%& condition is true (see section &<<SECTscanvirus>>&).
+.vitem &$max_received_linelength$&
+.vindex "&$max_received_linelength$&"
+.cindex "maximum" "line length"
+.cindex "line length" "maximum"
+This variable contains the number of bytes in the longest line that was
+received as part of the message, not counting the line termination
+character(s).
.vitem &$message_age$&
.cindex "message" "age of"
.cindex "message body" "in expansion"
.cindex "binary zero" "in message body"
.vindex "&$message_body$&"
-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.
+.oindex "&%message_body_visible%&"
+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.
+
+.oindex "&%message_body_newlines%&"
+By default, newlines are converted into spaces in &$message_body$&, to make it
+easier to search for phrases that might be split over a line break. However,
+this can be disabled by setting &%message_body_newlines%& to be true. Binary
+zeros are always converted into spaces.
.vitem &$message_body_end$&
.cindex "body of message" "expansion variable"
&$message_body_size$&, &$body_linecount$&, and &$body_zerocount$&.
.cindex "RCPT" "value of &$message_size$&"
-While running an ACL at the time of an SMTP RCPT command, &$message_size$&
+While running a per message ACL (mail/rcpt/predata), &$message_size$&
contains the size supplied on the MAIL command, or -1 if no size was given. The
value may not, of course, be truthful.
&%acl_smtp_mime%&, &%acl_not_smtp_start%&, &%acl_not_smtp%&, and
&%acl_not_smtp_mime%&.
.next
-.new
From within a &[local_scan()]& function.
-.wen
.endlist
about the failure. The details are the same as for
&$recipient_verify_failure$&.
-.new
.vitem &$sending_ip_address$&
.vindex "&$sending_ip_address$&"
This variable is set whenever an outgoing SMTP connection to another host has
This variable is set whenever an outgoing SMTP connection to another host has
been set up. It contains the local port that is being used. For incoming
connections, see &$received_port$&.
-.wen
.vitem &$smtp_active_hostname$&
.vindex "&$smtp_active_hostname$&"
space removed. Following the introduction of &$smtp_command$&, this variable is
somewhat redundant, but is retained for backwards compatibility.
-.new
.vitem &$smtp_count_at_connection_start$&
.vindex "&$smtp_count_at_connection_start$&"
This variable is set greater than zero only in processes spawned by the Exim
there actually are, because many other connections may come and go while a
single connection is being processed. When a child process terminates, the
daemon decrements its copy of the variable.
-.wen
.vitem "&$sn0$& &-- &$sn9$&"
These variables are copies of the values of the &$n0$& &-- &$n9$& accumulators
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.
+received over unencrypted connections, the variable is empty. Testing
+&$tls_cipher$& for emptiness is one way of distinguishing between encrypted and
+non-encrypted connections during ACL processing.
+
+The &$tls_cipher$& variable retains its value during message delivery, except
+when an outward SMTP delivery takes place via the &(smtp)& transport. In this
+case, &$tls_cipher$& is cleared before any outgoing SMTP connection is made,
+and then set to the outgoing cipher suite if one is negotiated. See chapter
+&<<CHAPTLS>>& for details of TLS support and chapter &<<CHAPsmtptrans>>& for
+details of the &(smtp)& transport.
.vitem &$tls_peerdn$&
.vindex "&$tls_peerdn$&"
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.
+&$tls_peerdn$& during subsequent processing. Like &$tls_cipher$&, the
+value is retained during message delivery, except during outbound SMTP
+deliveries.
.vitem &$tod_bsdinbox$&
.vindex "&$tod_bsdinbox$&"
.vitem &$value$&
.vindex "&$value$&"
This variable contains the result of an expansion lookup, extraction operation,
-or external command, as described above. &new("It is also used during a
-&*reduce*& expansion.")
+or external command, as described above. It is also used during a
+&*reduce*& expansion.
.vitem &$version_number$&
.vindex "&$version_number$&"
.row &%disable_ipv6%& "do no IPv6 processing"
.row &%keep_malformed%& "for broken files &-- should not happen"
.row &%localhost_number%& "for unique message ids in clusters"
+.row &%message_body_newlines%& "retain newlines in &$message_body$&"
.row &%message_body_visible%& "how much to show in &$message_body$&"
.row &%mua_wrapper%& "run in &""MUA wrapper""& mode"
.row &%print_topbitchars%& "top-bit characters are printing"
.section "Data lookups" "SECID101"
.table2
+.row &%ibase_servers%& "InterBase servers"
.row &%ldap_default_servers%& "used if no server in query"
.row &%ldap_version%& "set protocol version"
.row &%lookup_open_max%& "lookup files held open"
-.row &%mysql_servers%& "as it says"
-.row &%oracle_servers%& "as it says"
-.row &%pgsql_servers%& "as it says"
+.row &%mysql_servers%& "default MySQL servers"
+.row &%oracle_servers%& "Oracle servers"
+.row &%pgsql_servers%& "default PostgreSQL servers"
.row &%sqlite_lock_timeout%& "as it says"
.endtable
.row &%check_spool_space%& "before accepting a message"
.row &%deliver_queue_load_max%& "no queue deliveries if load high"
.row &%queue_only_load%& "queue incoming if load high"
+.row &%queue_only_load_latch%& "don't re-evaluate load for each message"
.row &%queue_run_max%& "maximum simultaneous queue runners"
.row &%remote_max_parallel%& "parallel SMTP delivery per message"
.row &%smtp_accept_max%& "simultaneous incoming connections"
.row &%acl_smtp_auth%& "ACL for AUTH"
.row &%acl_smtp_connect%& "ACL for connection"
.row &%acl_smtp_data%& "ACL for DATA"
+.row &%acl_smtp_dkim%& "ACL for DKIM verification"
.row &%acl_smtp_etrn%& "ACL for ETRN"
.row &%acl_smtp_expn%& "ACL for EXPN"
.row &%acl_smtp_helo%& "ACL for EHLO or HELO"
.section "TLS" "SECID108"
.table2
-.row &new(&%gnutls_require_kx%&) "control GnuTLS key exchanges"
-.row &new(&%gnutls_require_mac%&) "control GnuTLS MAC algorithms"
-.row &new(&%gnutls_require_protocols%&) "control GnuTLS protocols"
+.row &%gnutls_require_kx%& "control GnuTLS key exchanges"
+.row &%gnutls_require_mac%& "control GnuTLS MAC algorithms"
+.row &%gnutls_require_protocols%& "control GnuTLS protocols"
+.row &%gnutls_compat_mode%& "use GnuTLS compatibility mode"
+.row &%openssl_options%& "adjust OpenSSL compatibility options"
.row &%tls_advertise_hosts%& "advertise TLS to these hosts"
.row &%tls_certificate%& "location of server certificate"
.row &%tls_crl%& "certificate revocation list"
.row &%queue_only%& "no immediate delivery at all"
.row &%queue_only_file%& "no immediate delivery if file exists"
.row &%queue_only_load%& "no immediate delivery if load is high"
+.row &%queue_only_load_latch%& "don't re-evaluate load for each message"
.row &%queue_only_override%& "allow command line to override"
.row &%queue_run_in_order%& "order of arrival"
.row &%queue_run_max%& "of simultaneous queue runners"
.row &%bounce_return_message%& "include original message in bounce"
.row &%bounce_return_size_limit%& "limit on returned message"
.row &%bounce_sender_authentication%& "send authenticated sender with bounce"
-.row &new(&%dsn_from%&) "set &'From:'& contents in bounces"
+.row &%dsn_from%& "set &'From:'& contents in bounces"
.row &%errors_copy%& "copy bounce messages"
.row &%errors_reply_to%& "&'Reply-to:'& in bounces"
.row &%delay_warning%& "time schedule"
.code
sophie:/var/run/sophie
.endd
-If the value of &%av_scanner%& starts with dollar character, it is expanded
+If the value of &%av_scanner%& starts with a dollar character, it is expanded
before use. See section &<<SECTscanvirus>>& for further details.
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.
-.new
-.option disable_fnync main boolean false
+.option disable_fsync main boolean false
.cindex "&[fsync()]&, disabling"
This option is available only if Exim was built with the compile-time option
ENABLE_DISABLE_FSYNC. When this is not set, a reference to &%disable_fsync%& in
updated files' data to be written to disc before continuing. Unexpected events
such as crashes and power outages may cause data to be lost or scrambled.
Here be Dragons. &*Beware.*&
-.wen
.option disable_ipv6 main boolean false
(?i)^(?>(?(1)\.|())[^\W_](?>[a-z0-9/-]*[^\W_])?)+$
.endd
which permits only letters, digits, slashes, and hyphens in components, but
-they must start and end with a letter or digit. Hyphens are not, in fact,
+they must start and end with a letter or digit. Slashes are not, in fact,
permitted in host names, but they are found in certain NS records (which can be
accessed in Exim by using a &%dnsdb%& lookup). If you set
&%allow_utf8_domains%&, you must modify this pattern, or set the option to an
handled CR and LF characters in incoming messages. What happens now is
described in section &<<SECTlineendings>>&.
-.new
.option dsn_from main "string&!!" "see below"
.cindex "&'From:'& header line" "in bounces"
.cindex "bounce messages" "&'From:'& line, specifying"
.endd
The value is expanded every time it is needed. If the expansion fails, a
panic is logged, and the default value is used.
-.wen
.option envelope_to_remove main boolean true
.cindex "&'Envelope-to:'& header line"
See &%gecos_name%& above.
-.new
.option gnutls_require_kx main string unset
This option controls the key exchange mechanisms when GnuTLS is used in an Exim
server. For details, see section &<<SECTreqciphgnu>>&.
.option gnutls_require_protocols main string unset
This option controls the protocols when GnuTLS is used in an Exim
server. For details, see section &<<SECTreqciphgnu>>&.
-.wen
+.option gnutls_compat_mode main boolean unset
+This option controls whether GnuTLS is used in compatibility mode in an Exim
+server. This reduces security slightly, but improves interworking with older
+implementations of TLS.
.option headers_charset main string "see below"
This option sets a default character set for translating from encoded MIME
By default, Exim just checks the syntax of HELO and EHLO commands (see
&%helo_accept_junk_hosts%& and &%helo_allow_chars%&). However, some sites like
to do more extensive checking of the data supplied by these commands. The ACL
-condition &`verify`& &`=`& &`helo`& is provided to make this possible.
+condition &`verify = helo`& is provided to make this possible.
Formerly, it was necessary also to set this option (&%helo_try_verify_hosts%&)
to force the check to occur. From release 4.53 onwards, this is no longer
-necessary. If the check has not been done before &`verify`& &`=`& &`helo`& is
+necessary. If the check has not been done before &`verify = helo`& is
encountered, it is done at that time. Consequently, this option is obsolete.
Its specification is retained here for backwards compatibility.
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.
+be detected later in an ACL by the &`verify = helo`& condition.
.option helo_verify_hosts main "host list&!!" unset
.cindex "HELO verifying" "mandatory"
.vindex "&$sender_host_name$&"
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.
+&%dns_again_means_nonexist%&, &%helo_lookup_domains%&, and
+&`verify = reverse_host_lookup`& in ACLs.
.option host_lookup_order main "string list" &`bydns:byaddr`&
interfaces and recognizing the local host.
+.option ibase_servers main "string list" unset
+.cindex "InterBase" "server list"
+This option provides a list of InterBase servers and associated connection data,
+to be used in conjunction with &(ibase)& lookups (see section &<<SECID72>>&).
+The option is available only if Exim has been built with InterBase support.
+
+
+
.option ignore_bounce_errors_after main time 10w
.cindex "bounce message" "discarding"
.cindex "discarding bounce message"
an argument that is longer behaves as if &[getpwnam()]& failed.
+.option message_body_newlines main bool false
+.cindex "message body" "newlines in variables"
+.cindex "newline" "in message body variables"
+.vindex "&$message_body$&"
+.vindex "&$message_body_end$&"
+By default, newlines in the message body are replaced by spaces when setting
+the &$message_body$& and &$message_body_end$& expansion variables. If this
+option is set true, this no longer happens.
+
.option message_body_visible main integer 500
.cindex "body of message" "visible size"
the generic transport option &%message_size_limit%&, which limits the size of
message that an individual transport can process.
+.new
+If you use a virus-scanner and set this option to to a value larger than the
+maximum size that your virus-scanner is configured to support, you may get
+failures triggered by large mails. The right size to configure for the
+virus-scanner depends upon what data is passed and the options in use but it's
+probably safest to just set it to a little larger than this value. Eg, with a
+default Exim message size of 50M and a default ClamAV StreamMaxLength of 10M,
+some problems may result.
+.wen
+
.option move_frozen_messages main boolean false
.cindex "frozen messages" "moving"
.option mysql_servers main "string list" unset
.cindex "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
+be used in conjunction with &(mysql)& lookups (see section &<<SECID72>>&). The
option is available only if Exim has been built with MySQL support.
transport driver.
+.new
+.option openssl_options main "string list" +dont_insert_empty_fragments
+.cindex "OpenSSL "compatibility options"
+This option allows an administrator to adjust the SSL options applied
+by OpenSSL to connections. It is given as a space-separated list of items,
+each one to be +added or -subtracted from the current value. The default
+value is one option which happens to have been set historically. You can
+remove all options with:
+.code
+openssl_options = -all
+.endd
+This option is only available if Exim is built against OpenSSL. The values
+available for this option vary according to the age of your OpenSSL install.
+The &"all"& value controls a subset of flags which are available, typically
+the bug workaround options. The &'SSL_CTX_set_options'& man page will
+list the values known on your system and Exim should support all the
+&"bug workaround"& options and many of the &"modifying"& options. The Exim
+names lose the leading &"SSL_OP_"& and are lower-cased.
+
+Note that adjusting the options can have severe impact upon the security of
+SSL as used by Exim. It is possible to disable safety checks and shoot
+yourself in the foot in various unpleasant ways. This option should not be
+adjusted lightly. An unrecognised item will be detected at by invoking Exim
+with the &%-bV%& flag.
+
+An example:
+.code
+openssl_options = -all +microsoft_big_sslv3_buffer
+.endd
+.wen
+
+
.option oracle_servers main "string list" unset
.cindex "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>>&).
+to be used in conjunction with &(oracle)& lookups (see section &<<SECID72>>&).
The option is available only if Exim has been built with Oracle support.
.cindex "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
+&<<SECID72>>&). The option is available only if Exim has been built with
PostgreSQL support.
.option pipelining_advertise_hosts main "host list&!!" *
.cindex "PIPELINING" "suppressing advertising"
This option can be used to suppress the advertisement of the SMTP
-PIPELINING extension to specific hosts. &new("See also the &*no_pipelining*&
-control in section &<<SECTcontrols>>&.") When PIPELINING is not advertised and
+PIPELINING extension to specific hosts. See also the &*no_pipelining*&
+control in section &<<SECTcontrols>>&. When PIPELINING is not advertised and
&%smtp_enforce_sync%& is true, an Exim server enforces strict synchronization
for each SMTP command and response. When PIPELINING is advertised, Exim assumes
that clients will use it; &"out of order"& commands that are &"expected"& do
.cindex "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%&.
+happens during local or remote SMTP input, all subsequent messages received on
+the same SMTP connection are queued by default, whatever happens to the load in
+the meantime, but this can be changed by setting &%queue_only_load_latch%&
+false.
+
+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%&.
+
+
+.option queue_only_load_latch main boolean true
+.cindex "load average" "re-evaluating per message"
+When this option is true (the default), once one message has been queued
+because the load average is higher than the value set by &%queue_only_load%&,
+all subsequent messages received on the same SMTP connection are also queued.
+This is a deliberate choice; even though the load average may fall below the
+threshold, it doesn't seem right to deliver later messages on the same
+connection when not delivering earlier ones. However, there are special
+circumstances such as very long-lived connections from scanning appliances
+where this is not the best strategy. In such cases, &%queue_only_load_latch%&
+should be set false. This causes the value of the load average to be
+re-evaluated for each message.
.option queue_only_override main boolean true
non-zero if either &%smtp_accept_max_per_host%& or &%smtp_accept_queue%& is
set. See also &%smtp_accept_reserve%& and &%smtp_load_reserve%&.
-.new
A new SMTP connection is immediately rejected if the &%smtp_accept_max%& limit
has been reached. If not, Exim first checks &%smtp_accept_max_per_host%&. If
that limit has not been reached for the client host, &%smtp_accept_reserve%&
and &%smtp_load_reserve%& are then checked before accepting the connection.
-.wen
.option smtp_accept_max_nonmail main integer 10
.option smtp_accept_max_per_host main string&!! unset
.cindex "limit" "SMTP connections from one host"
.cindex "host" "limiting SMTP connections from"
-.new
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
is entirely independent of &%smtp_accept_reserve%&. The option's default value
of zero imposes no limit. If this option is set greater than zero, it is
required that &%smtp_accept_max%& be non-zero.
-.wen
&*Warning*&: When setting this option you should not use any expansion
constructions that take an appreciable amount of time. The expansion and test
.cindex "SMTP" "incoming connection count"
.cindex "queueing incoming messages"
.cindex "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%&&'x'&
-command line options.
+If the number of simultaneous incoming SMTP connections being handled via the
+listening daemon exceeds this value, messages received by SMTP are just placed
+on the queue; no delivery processes are started automatically. The count is
+fixed at the start of an SMTP connection. It cannot be updated in the
+subprocess that receives messages, and so the queueing or not queueing applies
+to all messages received in the same connection.
+
+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%&&'x'& command line options.
. Allow this long option name to split; give it unsplit as a fifth argument
&%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 this group
-of hosts can always get at least &%smtp_accept_reserve%& connections.
-&new("However, the limit specified by &%smtp_accept_max_per_host%& is still
-applied to each individual host.")
+of hosts can always get at least &%smtp_accept_reserve%& connections. However,
+the limit specified by &%smtp_accept_max_per_host%& is still applied to each
+individual host.
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%&,
-&new("provided the other criteria for acceptance are met.")
+provided the other criteria for acceptance are met.
.option smtp_active_hostname main string&!! unset
This specifies the transport driver that is to be used when a &%mail%& command
is used in a system filter.
+.new
.option system_filter_user main string unset
.cindex "uid (user id)" "system filter"
-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
+If this option is set to root, the system filter is run in the main Exim
+delivery process, as root. Otherwise, the system filter runs in a separate
+process, as the given user, defaulting to the Exim run-time 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,
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.
+transport option overrides.
+.wen
.option tcp_nodelay main boolean true
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.
+These certificates should be for the certificate authorities trusted, rather
+than the public cert of individual clients. With both OpenSSL and GnuTLS, if
+the value is a file then the certificates are sent by Exim as a server to
+connecting clients, defining the list of accepted certificate authorities.
+Thus the values defined should be considered public data. To avoid this,
+use OpenSSL with a directory.
+
.option tls_verify_hosts main "host list&!!" unset
.cindex "TLS" "client certificate verification"
.cindex "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.
+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.
+&%tls_verify_certificates%&. When the client initiates a TLS session, it must
+present one of the listed certificates. If it does not, the connection is
+aborted. &*Warning*&: Including a host in &%tls_verify_hosts%& does not require
+the host to use TLS. It can still send SMTP commands through unencrypted
+connections. Forcing a client to use TLS has to be done separately using an
+ACL to reject inappropriate commands when the connection is not encrypted.
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
This makes the configuration file less messy, and also reduces the number of
lookups (though Exim does cache lookups).
-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
-
.vindex "&$sender_address_data$&"
.vindex "&$address_data$&"
-When &$address_data$& is set by a router when verifying a recipient address
-from an ACL, it remains available for use in the rest of the ACL statement.
-After verifying a sender, the value is transferred to &$sender_address_data$&.
-
+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 a recipient address from an
+ACL, it remains available for use in the rest of the ACL statement. After
+verifying a sender, the value is transferred to &$sender_address_data$&.
If the result is any other value, the router is run (as this is the last
precondition to be evaluated, all the other preconditions must be true).
+.new
+This option is unique in that multiple &%condition%& options may be present.
+All &%condition%& options must succeed.
+.wen
+
The &%condition%& option provides a means of applying custom conditions to the
running of routers. Note that in the case of a simple conditional expansion,
the default expansion values are exactly what is wanted. For example:
.code
condition = ${if >{$message_age}{600}{true}{}}
.endd
+.new
+A multiple condition example, which succeeds:
+.code
+condition = ${if >{$message_age}{600}}
+condition = ${if !eq{${lc:$local_part}}{postmaster}}
+condition = foobar
+.endd
+.wen
If the expansion fails (other than forced failure) delivery is deferred. Some
of the other precondition options are common special cases that could in fact
be specified using &%condition%&.
&*Warning 1*&: The &%headers_add%& option cannot be used for a &(redirect)&
router that has the &%one_time%& option set.
-.new
.cindex "duplicate addresses"
.oindex "&%unseen%&"
&*Warning 2*&: If the &%unseen%& option is set on the router, all header
circumstances, to pipes -- see section &<<SECTdupaddr>>&), but it is undefined
which of the duplicates is discarded, so this ambiguous situation should be
avoided. The &%repeat_use%& option of the &%redirect%& router may be of help.
-.wen
&*Warning 1*&: The &%headers_remove%& option cannot be used for a &(redirect)&
router that has the &%one_time%& option set.
-.new
&*Warning 2*&: If the &%unseen%& option is set on the router, all header
removal requests are deleted when the address is passed on to subsequent
routers, and this can lead to problems with duplicates -- see the similar
warning for &%headers_add%& above.
-.wen
.option ignore_target_hosts routers "host list&!!" unset
check_local_user
transport = local_delivery
.endd
+For security, it would probably be a good idea to restrict the use of this
+router to locally-generated messages, using a condition such as this:
+.code
+ condition = ${if match {$sender_host_address}\
+ {\N^(|127\.0\.0\.1)$\N}}
+.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
.option pass_router routers string unset
.cindex "router" "go to after &""pass""&"
-When a router returns &"pass"&, the address is normally handed on to the next
+Routers that recognize the generic &%self%& option (&(dnslookup)&,
+&(ipliteral)&, and &(manualroute)&) are able to return &"pass"&, forcing
+routing to continue, and overriding a false setting of &%more%&. When one of
+these routers 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"&.
+&"decline"& because it cannot handle an address.
the value of &%unseen%& contains expansion items (and therefore, presumably, is
sometimes true and sometimes false).
-.new
.cindex "copy of message (&%unseen%& option)"
Setting the &%unseen%& option has a similar effect to the &%unseen%& command
qualifier in filter files. It can be used to cause copies of messages to be
Unlike the handling of header modifications, any data that was set by the
&%address_data%& option in the current or previous routers &'is'& passed on to
subsequent routers.
-.wen
.option user routers string&!! "see below"
.cindex "options" "&(manualroute)& router"
The private options for the &(manualroute)& router are as follows:
-.new
.option host_all_ignored manualroute string defer
See &%host_find_failed%&.
The &%host_find_failed%& 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.
-.wen
.option hosts_randomize manualroute boolean false
.next
It can cause an automatic reply to be generated.
.next
-.new
It can be forced to fail, optionally with a custom error message.
.next
It can be temporarily deferred, optionally with a custom message.
-.wen
.next
It can be discarded.
.endlist
:defer:
: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:
+respectively. When a redirection list contains such an item, it applies
+to the entire redirection; any other items in the list are ignored. Any
+text following &':fail:'& or &':defer:'& is placed in the error text
+associated with the failure. For example, an alias file might contain:
.code
X.Employee: :fail: Gone away, no forwarding address
.endd
local_part_prefix = real-
transport = local_delivery
.endd
+For security, it would probably be a good idea to restrict the use of this
+router to locally-generated messages, using a condition such as this:
+.code
+ condition = ${if match {$sender_host_address}\
+ {\N^(|127\.0\.0\.1)$\N}}
+.endd
+
.option syntax_errors_text redirect string&!! unset
See &%skip_syntax_errors%& above.
are all run in parallel, like a shell pipeline.
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.
+care not to break RFC 2822 syntax. 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.
.cindex "content scanning" "per user"
A transport filter can be used to provide content-scanning on a per-user basis
message_prefix = "From ${if def:return_path{$return_path}\
{MAILER-DAEMON}} $tod_bsdinbox\n"
.endd
-
+&*Note:*& If you set &%use_crlf%& true, you must change any occurrences of
+&`\n`& to &`\r\n`& in &%message_prefix%&.
.option message_suffix appendfile string&!! "see below"
The string specified here is expanded and output at the end of every message.
.code
message_suffix =
.endd
+&*Note:*& If you set &%use_crlf%& true, you must change any occurrences of
+&`\n`& to &`\r\n`& in &%message_suffix%&.
.option mode appendfile "octal integer" 0600
If the output file is created, it is given this mode. If it already exists and
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.
+&*Note:*& The contents of the &%message_prefix%& and &%message_suffix%& options
+(which are used to supply the traditional &"From&~"& and blank line separators
+in Berkeley-style mailboxes) 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.
.option use_fcntl_lock appendfile boolean "see below"
.option timeout lmtp 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. Here is an
-example of a typical LMTP transport:
+respond to LMTP commands or message input within this timeout. Delivery
+is deferred, and will be tried again later. Here is an example of a typical
+LMTP transport:
.code
lmtp:
driver = lmtp
.code
message_prefix =
.endd
+&*Note:*& If you set &%use_crlf%& true, you must change any occurrences of
+&`\n`& to &`\r\n`& in &%message_prefix%&.
+
.option message_suffix pipe string&!! "see below"
The string specified here is expanded and output at the end of every message.
.code
message_suffix =
.endd
+&*Note:*& If you set &%use_crlf%& true, you must change any occurrences of
+&`\n`& to &`\r\n`& in &%message_suffix%&.
+
.option path pipe string "see below"
This option specifies the string that is set up in the PATH environment
apply to a command specified as a transport filter.
+.new
+.option permit_coredump pipe boolean false
+Normally Exim inhibits core-dumps during delivery. If you have a need to get
+a core-dump of a pipe command, enable this command. This enables core-dumps
+during delivery and affects both the Exim binary and the pipe command run.
+It is recommended that this option remain off unless and until you have a need
+for it and that this only be enabled when needed, as the risk of excessive
+resource consumption can be quite high. Note also that Exim is typically
+installed as a setuid binary and most operating systems will inhibit coredumps
+of these by default, so further OS-specific action may be required.
+.wen
+
+
.option pipe_as_creator pipe boolean false
.cindex "uid (user id)" "local delivery"
If the generic &%user%& option is not set and this option is true, the delivery
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.
+are needed. When &%use_bsmtp%& is not set, the default values for both
+&%message_prefix%& and &%message_suffix%& end with a single linefeed, so their
+values must be changed to end with &`\r\n`& if &%use_crlf%& is set.
.option use_shell pipe boolean false
envelope_to_add
check_string = "From "
escape_string = ">From "
+ umask = 077
user = $local_part
group = mail
-.section "Use of the $host variable" "SECID145"
+.section "Use of the $host and $host_address variables" "SECID145"
.vindex "&$host$&"
.vindex "&$host_address$&"
At the start of a run of the &(smtp)& transport, the values of &$host$& and
&%serialize_hosts%&, and the various TLS options are expanded.
+.section "Use of $tls_cipher and $tls_peerdn" "usecippeer"
+.vindex &$tls_cipher$&
+.vindex &$tls_peerdn$&
+At the start of a run of the &(smtp)& transport, the values of &$tls_cipher$&
+and &$tls_peerdn$& are the values that were set when the message was received.
+These are the values that are used for options that are expanded before any
+SMTP connections are made. Just before each connection is made, these two
+variables are emptied. If TLS is subsequently started, they are set to the
+appropriate values for the outgoing connection, and these are the values that
+are in force when any authenticators are run and when the
+&%authenticated_sender%& option is expanded.
+
.section "Private options for smtp" "SECID146"
.cindex "options" "&(smtp)& transport"
to be deferred. If the result of expansion is an empty string, that is also
ignored.
+The expansion happens after the outgoing connection has been made and TLS
+started, if required. This means that the &$host$&, &$host_address$&,
+&$tls_cipher$&, and &$tls_peerdn$& variables are set according to the
+particular connection.
+
If the SMTP session is not authenticated, the expansion of
&%authenticated_sender%& still happens (and can cause the delivery to be
deferred if it fails), but no AUTH= item is added to MAIL commands
instead of using the DNS. Of course, that function may in fact use the DNS, but
it may also consult other sources of information such as &_/etc/hosts_&.
-.new
-.option gnutls_require_kx main string unset
+.option gnutls_require_kx smtp string unset
This option controls the key exchange mechanisms when GnuTLS is used in an Exim
client. For details, see section &<<SECTreqciphgnu>>&.
-.option gnutls_require_mac main string unset
+.option gnutls_require_mac smtp string unset
This option controls the MAC algorithms when GnuTLS is used in an Exim
client. For details, see section &<<SECTreqciphgnu>>&.
-.option gnutls_require_protocols main string unset
+.option gnutls_require_protocols smtp string unset
This option controls the protocols when GnuTLS is used in an Exim
client. For details, see section &<<SECTreqciphgnu>>&.
-.wen
-.new
+.option gnutls_compat_mode smtp boolean unset
+This option controls whether GnuTLS is used in compatibility mode in an Exim
+server. This reduces security slightly, but improves interworking with older
+implementations of TLS.
+
.option helo_data smtp string&!! "see below"
.cindex "HELO" "argument, setting"
.cindex "EHLO" "argument, setting"
During the expansion, the variables &$host$& and &$host_address$& are set to
the identity of the remote host, and the variables &$sending_ip_address$& and
&$sending_port$& are set to the local IP address and port number that are being
-used. These variables can be therefore used to generate different values for
-different servers or different local IP addresses. For example, if you want the
-string that is used for &%helo_data%& to be obtained by a DNS lookup of the
-outgoing interface address, you could use this:
+used. These variables can be used to generate different values for different
+servers or different local IP addresses. For example, if you want the string
+that is used for &%helo_data%& to be obtained by a DNS lookup of the outgoing
+interface address, you could use this:
.code
helo_data = ${lookup dnsdb{ptr=$sending_ip_address}{$value}\
{$primary_hostname}}
.endd
The use of &%helo_data%& applies both to sending messages and when doing
callouts.
-.wen
.option hosts smtp "string list&!!" unset
Hosts are associated with an address by a router such as &(dnslookup)&, which
facilities such as AUTH, PIPELINING, SIZE, and STARTTLS.
-.new
.option hosts_avoid_pipelining smtp "host list&!!" unset
.cindex "PIPELINING" "avoiding the use of"
Exim will not use the SMTP PIPELINING extension when delivering to any host
that matches this list, even if the server host advertises PIPELINING support.
-.wen
.option hosts_avoid_tls smtp "host list&!!" unset
.vindex "&$host$&"
.vindex "&$host_address$&"
This option specifies which interface to bind to when making an outgoing SMTP
-call. &*Note:*& Do not confuse this with the interface address that was used
-when a message was received, which is in &$received_ip_address$&, formerly
-known as &$interface_address$&. The name was changed to minimize confusion with
-the outgoing interface address. There is no variable that contains an outgoing
+call. The value is an IP address, not an interface name such as
+&`eth0`&. Do not confuse this with the interface address that was used when a
+message was received, which is in &$received_ip_address$&, formerly known as
+&$interface_address$&. The name was changed to minimize confusion with the
+outgoing interface address. There is no variable that contains an outgoing
interface address because, unless it is set by this option, its value is
unknown.
&`s`& rewrite the &'Sender:'& header
&`t`& rewrite the &'To:'& header
.endd
+"All headers" means all of the headers listed above that can be selected
+individually, plus their &'Resent-'& versions. It does not include
+other headers such as &'Subject:'& etc.
+
You should be particularly careful about rewriting &'Sender:'& headers, and
restrict this to special known cases in your own domains.
.chapter "Retry configuration" "CHAPretry"
.scindex IIDretconf1 "retry" "configuration, description of"
.scindex IIDregconf2 "configuration file" "retry section"
-The &"retry"& section of the run time configuration file contains a list of
+The &"retry"& section of the runtime configuration file contains a list of
retry rules that 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, domain and error.
+be delivered at the first attempt. If there are no retry rules (the section is
+empty or not present), there are no retries. In this situation, temporary
+errors are treated as permanent. The default configuration contains a single,
+general-purpose retry rule (see section &<<SECID57>>&). The &%-brt%& command
+line option can be used to test which retry rule will be used for a given
+address, domain and error.
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.
&`$ `&&*&`telnet server.example 25`&*&
&`Trying 192.168.34.25...`&
&`Connected to server.example.`&
-&`Escape character is '^]'.`&
+&`Escape character is '^]'.`&
&`220 server.example ESMTP Exim 4.20 ...`&
&*&`ehlo client.example`&*&
&`250-server.example Hello client.example [10.8.4.5]`&
.cindex "authentication" "generic options"
.cindex "options" "generic; for authenticators"
+.option client_condition authenticators string&!! unset
+When Exim is authenticating as a client, it skips any authenticator whose
+&%client_condition%& expansion yields &"0"&, &"no"&, or &"false"&. This can be
+used, for example, to skip plain text authenticators when the connection is not
+encrypted by a setting such as:
+.code
+client_condition = ${if !eq{$tls_cipher}{}}
+.endd
+(Older documentation incorrectly states that &$tls_cipher$& contains the cipher
+used for incoming messages. In fact, during SMTP delivery, it contains the
+cipher used for the delivery.)
+
.option driver authenticators string unset
This option must always be set. It specifies which of the available
of these options, Exim (as a client) tries to authenticate as follows:
.ilist
-.new
For each authenticator that is configured as a client, in the order in which
they are defined in the configuration, it searches the authentication
mechanisms announced by the server for one whose name matches the public name
of the authenticator.
-.wen
.next
.vindex "&$host$&"
.vindex "&$host_address$&"
driver = plaintext
public_name = LOGIN
server_prompts = Username:: : Password::
- server_condition = ${if ldapauth \
- {user="cn=${quote_ldap_dn:$auth1},ou=people,o=example.org" \
- pass=${quote:$auth2} \
- ldap://ldap.example.org/}}
+ server_condition = ${if and{{ \
+ !eq{}{$auth1} }{ \
+ ldapauth{user="cn=${quote_ldap_dn:$auth1},ou=people,o=example.org" \
+ pass=${quote:$auth2} \
+ ldap://ldap.example.org/} }} }
server_set_id = uid=$auth1,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.
-
+We have to check that the username is not empty before using it, because LDAP
+does not permit empty DN components. We must also use 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" "SECID174"
sasl_plain:
driver = cyrus_sasl
public_name = PLAIN
- server_set_id = $auth1
+ server_set_id = $auth2
.endd
Cyrus SASL does implement the LOGIN authentication method, even though it is
not a standard method. It is disabled by default in the source distribution,
driver = dovecot
public_name = PLAIN
server_socket = /var/run/dovecot/auth-client
- server_set_id = $auth1
+ server_set_id = $auth2
dovecot_ntlm:
driver = dovecot
&$received_ip_address$& (that is, the connection is local), the &"secured"&
option is passed in the Dovecot authentication command. If, for a TLS
connection, a client certificate has been verified, the &"valid-client-cert"&
-option is passed. &new("When authentication succeeds, the identity of the user
-who authenticated is placed in &$auth1$&.")
+option is passed. When authentication succeeds, the identity of the user
+who authenticated is placed in &$auth1$&.
.ecindex IIDdcotauth1
.ecindex IIDdcotauth2
.section "GnuTLS parameter computation" "SECID181"
-GnuTLS uses RSA and D-H parameters that may take a substantial amount of time
+GnuTLS uses D-H parameters that may take a substantial amount of time
to compute. It is unreasonable to re-compute them for every TLS session.
Therefore, Exim keeps this data in a file in its spool directory, called
&_gnutls-params_&. The file is owned by the Exim user and is readable only by
-its owner. Every Exim process that start up GnuTLS reads the RSA and D-H
+its owner. Every Exim process that start up GnuTLS reads the D-H
parameters from this file. If the file does not exist, the first Exim process
that needs it computes the data and writes it to a temporary file which is
renamed once it is complete. It does not matter if several Exim processes do
-.new
.section "Requiring specific ciphers or other parameters in GnuTLS" &&&
"SECTreqciphgnu"
.cindex "GnuTLS" "specifying parameters for"
order for the cipher algorithms. The first one in the client's list that is
also advertised by the server is tried first. The default order is as listed
above.
-.wen
also included in the log line that records a message's arrival, keyed by
&"X="&, unless the &%tls_cipher%& log selector is turned off. The &%encrypted%&
condition can be used to test for specific cipher suites in ACLs.
-
-The ACLs that run for subsequent SMTP commands can check the name of the cipher
-suite and vary their actions accordingly. The cipher suite names are those used
-by OpenSSL. These may differ from the names used elsewhere. For example,
-OpenSSL uses the name DES-CBC3-SHA for the cipher suite which in other contexts
-is known as TLS_RSA_WITH_3DES_EDE_CBC_SHA. Check the OpenSSL
+(For outgoing SMTP deliveries, &$tls_cipher$& is reset &-- see section
+&<<SECID185>>&.)
+
+Once TLS has been established, 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 vary, depending on which TLS library is being used. 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 or GnuTLS
documentation for more details.
-
.section "Requesting and verifying client certificates" "SECID183"
.cindex "certificate" "verification of client"
.cindex "TLS" "client certificate verification"
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.
+&%tls_verify_hosts%& or &%tls_try_verify_hosts%& matches the client.
-If &%tls_verify_certificates%& is set, it must name a file or,
+If the &%tls_verify_certificates%& option is set on the &(smtp)& transport, it
+must name a file or,
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
the current host is abandoned, and the &(smtp)& transport tries to deliver to
alternative hosts, if any.
+ &*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.
+
.vindex "&$host$&"
.vindex "&$host_address$&"
All the TLS options in the &(smtp)& transport are expanded before use, with
which the client is connected. Forced failure of an expansion causes Exim to
behave as if the relevant option were unset.
+.vindex &$tls_cipher$&
+.vindex &$tls_peerdn$&
+Before an SMTP connection is established, the &$tls_cipher$& and &$tls_peerdn$&
+variables are emptied. (Until the first connection, they contain the values
+that were set when the message was received.) If STARTTLS is subsequently
+successfully obeyed, these variables are set to the relevant values for the
+outgoing connection.
+
.section "Multiple messages on the same encrypted TCP/IP connection" &&&
.irow &%acl_smtp_mail%& "ACL for MAIL"
.irow &%acl_smtp_mailauth%& "ACL for the AUTH parameter of MAIL"
.irow &%acl_smtp_mime%& "ACL for content-scanning MIME parts"
+.irow &%acl_smtp_notquit%& "ACL for non-QUIT terminations"
.irow &%acl_smtp_predata%& "ACL at start of DATA command"
.irow &%acl_smtp_quit%& "ACL for QUIT"
.irow &%acl_smtp_rcpt%& "ACL for RCPT"
The &%acl_not_smtp_start%& ACL is run right at the start of receiving a
non-SMTP message, before any of the message has been read. (This is the
-analogue of the &%acl_smtp_predata%& ACL for SMTP input.) &new("In the case of
-batched SMTP input, it runs after the DATA command has been reached.") The
+analogue of the &%acl_smtp_predata%& ACL for SMTP input.) In the case of
+batched SMTP input, it runs after the DATA command has been reached. The
result of this ACL is ignored; it cannot be used to reject a message. If you
really need to, you could set a value in an ACL variable here and reject based
on that in the &%acl_not_smtp%& ACL. However, this ACL can be used to set
your resources.
+.new
+.section "The SMTP DKIM ACL" "SECTDKIMACL"
+The &%acl_smtp_dkim%& ACL is available only when Exim is compiled with DKIM support
+enabled (which is the default).
+
+The ACL test specified by &%acl_smtp_dkim%& happens after a message has been
+received, and is executed for each DKIM signature found in a message. If not
+otherwise specified, the default action is to accept.
+
+For details on the operation of DKIM, see chapter &<<CHID12>>&.
+.wen
+
+
.section "The SMTP MIME ACL" "SECID194"
The &%acl_smtp_mime%& option is available only when Exim is compiled with the
content-scanning extension. For details, see chapter &<<CHAPexiscan>>&.
connection is closed. In these special cases, the QUIT ACL does not run.
+.section "The not-QUIT ACL" "SECTNOTQUITACL"
+.vindex &$acl_smtp_notquit$&
+The not-QUIT ACL, specified by &%acl_smtp_notquit%&, is run in most cases when
+an SMTP session ends without sending QUIT. However, when Exim itself is is bad
+trouble, such as being unable to write to its log files, this ACL is not run,
+because it might try to do things (such as write to log files) that make the
+situation even worse.
+
+Like the QUIT ACL, this ACL is provided to make it possible to do customized
+logging or to gather statistics, and its outcome is ignored. The &%delay%&
+modifier is forbidden in this ACL, and the only permitted verbs are &%accept%&
+and &%warn%&.
+
+.vindex &$smtp_notquit_reason$&
+When the not-QUIT ACL is running, the variable &$smtp_notquit_reason$& is set
+to a string that indicates the reason for the termination of the SMTP
+connection. The possible values are:
+.table2
+.irow &`acl-drop`& "Another ACL issued a &%drop%& command"
+.irow &`bad-commands`& "Too many unknown or non-mail commands"
+.irow &`command-timeout`& "Timeout while reading SMTP commands"
+.irow &`connection-lost`& "The SMTP connection has been lost"
+.irow &`data-timeout`& "Timeout while reading message data"
+.irow &`local-scan-error`& "The &[local_scan()]& function crashed"
+.irow &`local-scan-timeout`& "The &[local_scan()]& function timed out"
+.irow &`signal-exit`& "SIGTERM or SIGINT"
+.irow &`synchronization-error`& "SMTP synchronization error"
+.irow &`tls-failed`& "TLS failed to start"
+.endtable
+In most cases when an SMTP connection is closed without having received QUIT,
+Exim sends an SMTP response message before actually closing the connection.
+With the exception of the &`acl-drop`& case, the default message can be
+overridden by the &%message%& modifier in the not-QUIT ACL. In the case of a
+&%drop%& verb in another ACL, it is the message from the other ACL that is
+used.
+
.section "Finding an ACL to use" "SECID195"
.cindex "&ACL;" "finding which to use"
SMTP command is accepted. For example, in a RCPT ACL you could have:
.display
&`accept `&<&'some conditions'&>
-&` message = OK, I'll allow you through today`&
+&` message = OK, I will allow you through today`&
.endd
You can specify an SMTP response code, optionally followed by an &"extended
response code"& at the start of the message, but the first digit must be the
recipients to be discarded. If it 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.
+do not appear in the log line when the &%received_recipients%& log selector is set.
If the &%log_message%& modifier is set when &%discard%& operates,
its contents are added to the line that is automatically written to the log.
statement. If any of the conditions are not met, the ACL returns &"deny"&. For
example, when checking a RCPT command,
.code
-.new
require message = Sender did not verify
verify = sender
-.wen
.endd
passes control to subsequent statements only if the message's sender can be
-verified. Otherwise, it rejects the command. &new("Note the positioning of the
+verified. Otherwise, it rejects the command. Note the positioning of the
&%message%& modifier, before the &%verify%& condition. The reason for this is
-discussed in section &<<SECTcondmodproc>>&.")
+discussed in section &<<SECTcondmodproc>>&.
.next
.cindex "&%warn%& ACL verb"
incoming message, assuming, of course, that the message is ultimately
accepted. For details, see section &<<SECTaddheadacl>>&.
-.new
.vitem &*continue*&&~=&~<&'text'&>
.cindex "&%continue%& ACL modifier"
.cindex "database" "updating in ACL"
.display
&`continue = `&<&'some expansion'&>
.endd
-.wen
.vitem &*control*&&~=&~<&'text'&>
.cindex "&%control%& ACL modifier"
If you want to apply a control unconditionally, you can use it with a
&%require%& verb. For example:
.code
- require control = no_multiline_response
+ require control = no_multiline_responses
.endd
.endlist
.vitem &*delay*&&~=&~<&'time'&>
.cindex "&%delay%& ACL modifier"
.oindex "&%-bh%&"
-.new
This modifier may appear in any ACL. It causes Exim to wait for the time
interval before proceeding. However, when testing Exim using the &%-bh%&
option, the delay is not actually imposed (an appropriate message is output
instead). The time is given in the usual Exim notation, and the delay happens
as soon as the modifier is processed. In an SMTP session, pending output is
flushed before the delay is imposed.
-.wen
Like &%control%&, &%delay%& can be used with &%accept%& or &%deny%&, for
example:
accept ...
.endd
-.new
If &%delay%& is encountered when the SMTP PIPELINING extension is in use,
responses to several commands are no longer buffered and sent in one packet (as
they would normally be) because all output is flushed before imposing the
appear to the client as one large aggregated delay that might provoke an
unwanted timeout. You can, however, disable output flushing for &%delay%& by
using a &%control%& modifier to set &%no_delay_flush%&.
-.wen
.vitem &*endpass*&
&` log_reject_target =`&
.endd
This modifier can be used in SMTP and non-SMTP ACLs. It applies to both
-permanent and temporary rejections.
+permanent and temporary rejections. Its effect lasts for the rest of the
+current ACL.
.vitem &*logwrite*&&~=&~<&'text'&>
Notice that we put back the lower cased version afterwards, assuming that
is what is wanted for subsequent tests.
+.new
+.vitem &*control&~=&~debug/*&<&'options'&>
+.cindex "&ACL;" "enabling debug logging"
+.cindex "debugging" "enabling from an ACL"
+This control turns on debug logging, almost as though Exim had been invoked
+with &`-d`&, with the output going to a new logfile, by default called
+&'debuglog'&. The filename can be adjusted with the &'tag'& option, which
+may access any variables already defined. The logging may be adjusted with
+the &'opts'& option, which takes the same values as the &`-d`& command-line
+option. Some examples (which depend on variables that don't exist in all
+contexts):
+.code
+ control = debug
+ control = debug/tag=.$sender_host_address
+ control = debug/opts=+expand+acl
+ control = debug/tag=.$message_exim_id/opts=+expand
+.endd
+.wen
+
.vitem &*control&~=&~enforce_sync*& &&&
&*control&~=&~no_enforce_sync*&
.cindex "SMTP" "synchronization checking"
is told about the freezing), provided all the &*control=freeze*& modifiers that
are obeyed for the current message have the &`/no_tell`& option.
-.new
.vitem &*control&~=&~no_delay_flush*&
.cindex "SMTP" "output flushing, disabling for delay"
Exim normally flushes SMTP output before implementing a delay in an ACL, to
avoid unexpected timeouts in clients when the SMTP PIPELINING extension is in
use. This control, as long as it is encountered before the &%verify%& condition
that causes the callout, disables such output flushing.
-.wen
.vitem &*control&~=&~no_mbox_unspool*&
This control is available when Exim is compiled with the content scanning
the same SMTP connection. It is provided for debugging purposes and is unlikely
to be useful in production.
-.vitem &*control&~=&~no_multiline_response*&
+.vitem &*control&~=&~no_multiline_responses*&
.cindex "multiline responses, suppressing"
This control is permitted for any ACL except the one for non-SMTP messages.
It seems that there are broken clients in use that cannot handle multiline
The setting of the switch can, of course, be made conditional on the
calling host. Its effect lasts until the end of the SMTP connection.
-.new
.vitem &*control&~=&~no_pipelining*&
.cindex "PIPELINING" "suppressing advertising"
This control turns off the advertising of the PIPELINING extension to SMTP in
response to an EHLO command. Therefore, it should normally appear in an ACL
controlled by &%acl_smtp_connect%& or &%acl_smtp_helo%&. See also
&%pipelining_advertise_hosts%&.
-.wen
.vitem &*control&~=&~queue_only*&
.oindex "&%queue_only%&"
latter is the one defined by &%acl_smtp_predata%&). Setting it tells Exim that
the current message is a submission from a local MUA. In this case, Exim
operates in &"submission mode"&, and applies certain fixups to the message if
-necessary. For example, it add a &'Date:'& header line if one is not present.
+necessary. For example, it adds a &'Date:'& header line if one is not present.
This control is not permitted in the &%acl_smtp_data%& ACL, because that is too
late (the message has already been created).
.vitem &*control&~=&~suppress_local_fixups*&
.cindex "submission fixups, suppressing"
This control applies to locally submitted (non TCP/IP) messages, and is the
-complement of &`control`& &`=`& &`submission`&. It disables the fixups that are
+complement of &`control = submission`&. It disables the fixups that are
normally applied to locally-submitted messages. Specifically:
.ilist
and &%acl_not_smtp_start%& ACLs, because it has to be set before the message's
data is read.
-.new
&*Note:*& This control applies only to the current message, not to any others
that are being submitted at the same time using &%-bs%& or &%-bS%&.
-.wen
.endlist vlist
.ilist
Locally submitted, fixups applied: the default.
.next
-Locally submitted, no fixups applied: use &`control`& &`=`&
-&`suppress_local_fixups`&.
+Locally submitted, no fixups applied: use
+&`control = suppress_local_fixups`&.
.next
Remotely submitted, no fixups applied: the default.
.next
-Remotely submitted, fixups applied: use &`control`& &`=`& &`submission`&.
+Remotely submitted, fixups applied: use &`control = submission`&.
.endlist
This condition is available only when Exim is compiled with the
content-scanning extension, and it is allowed only in the ACL defined by
&%acl_smtp_mime%&. It causes the current MIME part to be decoded into a file.
-&new("If all goes well, the condition is true. It is false only if there are
+If all goes well, the condition is true. It is false only if there are
problems such as a syntax error or a memory shortage. For more details, see
-chapter &<<CHAPexiscan>>&.")
+chapter &<<CHAPexiscan>>&.
.vitem &*demime&~=&~*&<&'extension&~list'&>
.cindex "&%demime%& ACL condition"
&"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.
+&<<SECTmorednslists>>&&--&<<SECTmorednslistslast>>& for details.
.vitem &*domains&~=&~*&<&'domain&~list'&>
.cindex "&%domains%& ACL condition"
.cindex "&ACL;" "testing a DNS list"
In its simplest form, the &%dnslists%& condition tests whether the calling host
is on at least one of a number of DNS lists by looking up the inverted IP
-address in one or more DNS domains. For example, if the calling host's IP
+address in one or more DNS domains. (Note that DNS list domains are not mail
+domains, so the &`+`& syntax for named lists doesn't work - it is used for
+special options instead.) For example, if the calling host's IP
address is 192.168.62.43, and the ACL statement is
.code
deny dnslists = blackholes.mail-abuse.org : \
Thus, this example checks whether or not the IP addresses of the sender
domain's mail servers are on the Spamhaus black list.
+The key that was used for a successful DNS list lookup is put into the variable
+&$dnslist_matched$& (see section &<<SECID204>>&).
.endd
Section &<<SECTaddmatcon>>& below describes how you can distinguish between
different values. Some DNS lists may return more than one address record;
-&new("see section &<<SECThanmuldnsrec>>& for details of how they are checked.")
+see section &<<SECThanmuldnsrec>>& for details of how they are checked.
+
.section "Variables set from DNS lists" "SECID204"
+.cindex "expansion" "variables, set from DNS list"
.cindex "DNS list" "variables set from"
.vindex "&$dnslist_domain$&"
+.vindex "&$dnslist_matched$&"
.vindex "&$dnslist_text$&"
.vindex "&$dnslist_value$&"
-When an entry is found in a DNS list, the variable &$dnslist_domain$&
-contains the name of the domain that matched, and &$dnslist_value$& contains
-the data from the entry. If more than one address record is returned by the DNS
-lookup, all the IP addresses are included in &$dnslist_value$&, separated by
-commas and spaces. The variable &$dnslist_text$& contains the contents of any
-associated TXT record. For lists such as RBL+ the TXT record for a merged entry
-is often not very meaningful. See section &<<SECTmordetinf>>& for a way of
-obtaining more information.
+When an entry is found in a DNS list, the variable &$dnslist_domain$& contains
+the name of the overall domain that matched (for example,
+&`spamhaus.example`&), &$dnslist_matched$& contains the key within that domain
+(for example, &`192.168.5.3`&), and &$dnslist_value$& contains the data from
+the DNS record. When the key is an IP address, it is not reversed in
+&$dnslist_matched$& (though it is, of course, in the actual lookup). In simple
+cases, for example:
+.code
+deny dnslists = spamhaus.example
+.endd
+the key is also available in another variable (in this case,
+&$sender_host_address$&). In more complicated cases, however, this is not true.
+For example, using a data lookup (as described in section &<<SECTmulkeyfor>>&)
+might generate a dnslists lookup like this:
+.code
+deny dnslists = spamhaus.example/<|192.168.1.2|192.168.6.7|...
+.endd
+If this condition succeeds, the value in &$dnslist_matched$& might be
+&`192.168.6.7`& (for example).
+
+If more than one address record is returned by the DNS lookup, all the IP
+addresses are included in &$dnslist_value$&, separated by commas and spaces.
+The variable &$dnslist_text$& contains the contents of any associated TXT
+record. For lists such as RBL+ the TXT record for a merged entry is often not
+very meaningful. See section &<<SECTmordetinf>>& for a way of obtaining more
+information.
You can use the DNS list variables in &%message%& or &%log_message%& modifiers
&-- although these appear before the condition in the ACL, they are not
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. &new("For the moment, we assume
+any address record is considered to be a match. For the moment, we assume
that the DNS lookup returns just one record. Section &<<SECThanmuldnsrec>>&
-describes how multiple records are handled.")
+describes how multiple records are handled.
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
-.new
.section "Handling multiple DNS records from a DNS list" "SECThanmuldnsrec"
A DNS lookup for a &%dnslists%& condition may return more than one DNS record,
thereby providing more than one IP address. When an item in a &%dnslists%& list
.endlist
When the DNS lookup yields only a single IP address, there is no difference
between &`=`& and &`==`& and between &`&&`& and &`=&&`&.
-.wen
dnslists = some.list.example
.endd
-.section "Rate limiting senders" "SECTratelimiting"
+.section "Rate limiting incoming messages" "SECTratelimiting"
.cindex "rate limiting" "client sending"
.cindex "limiting client sending rates"
.oindex "&%smtp_ratelimit_*%&"
send in each time interval. It also specifies the number of messages permitted
in a fast burst. By increasing both &'m'& and &'p'& but keeping &'m/p'&
constant, you can allow a client to send more messages in a burst without
-changing its overall sending rate limit. Conversely, if &'m'& and &'p'& are
+changing its long-term sending rate limit. Conversely, if &'m'& and &'p'& are
both small, messages must be sent at an even rate.
There is a script in &_util/ratelimit.pl_& which extracts sending rates from
instructions when it is run with no arguments.
The key is used to look up the data for calculating the client's average
-sending rate. This data is stored in a database maintained by Exim in its spool
-directory, alongside the retry and other hints databases. The default key is
-&$sender_host_address$&, which applies the limit to each client host IP address.
+sending rate. This data is stored in Exim's spool directory, alongside the
+retry and other hints databases. The default key is &$sender_host_address$&,
+which means Exim computes the sending rate of each client host IP address.
By changing the key you can change how Exim identifies clients for the purpose
of ratelimiting. For example, to limit the sending rate of each authenticated
user, independent of the computer they are sending from, set the key to
&$authenticated_id$&. You must ensure that the lookup key is meaningful; for
example, &$authenticated_id$& is only meaningful if the client has
-authenticated, and you can check with the &%authenticated%& ACL condition.
+authenticated (which you can check with the &%authenticated%& ACL condition).
+
+The lookup key does not have to identify clients: If you want to limit the
+rate at which a recipient receives messages, you can use the key
+&`$local_part@$domain`& with the &%per_rcpt%& option (see below) in a RCPT
+ACL.
-Internally, Exim includes the smoothing constant &'p'& and the options in the
+Internally, Exim appends the smoothing constant &'p'& and the options onto the
lookup key because they alter the meaning of the stored data. This is not true
for the limit &'m'&, so you can alter the configured maximum rate and Exim will
still remember clients' past behaviour, but if you alter the other ratelimit
parameters Exim forgets past behaviour.
-Each &%ratelimit%& condition can have up to two options. The first option
+Each &%ratelimit%& condition can have up to three options. One option
specifies what Exim measures the rate of, and the second specifies how Exim
-handles excessively fast clients. The options are separated by a slash, like
-the other parameters.
+handles excessively fast clients. The third option can be &`noupdate`&, to
+disable updating of the ratelimiting database (see section &<<rearatdat>>&).
+The options are separated by a slash, like the other parameters. They may
+appear in any order.
+.section "Ratelimit options for what is being measured" "ratoptmea"
The &%per_conn%& option limits the client's connection rate.
The &%per_mail%& option limits the client's rate of sending messages. This is
The &%per_byte%& option limits the sender's email bandwidth. Note that it is
best to use this option in the DATA ACL; if it is used in an earlier ACL it
-relies on the SIZE parameter on the MAIL command, which may be inaccurate or
-completely missing. You can follow the limit &'m'& in the configuration with K,
-M, or G to specify limits in kilobytes, megabytes, or gigabytes, respectively.
+relies on the SIZE parameter specified by the client in its MAIL command,
+which may be inaccurate or completely missing. You can follow the limit &'m'&
+in the configuration with K, M, or G to specify limits in kilobytes,
+megabytes, or gigabytes, respectively.
+
+The &%per_rcpt%& option causes Exim to limit the rate at which
+recipients are accepted. To be effective, it would need to be used in
+either the &%acl_smtp_rcpt%& or the &%acl_not_smtp%& ACL. In the
+&%acl_smtp_rcpt%& ACL, the number of recipients is incremented by one.
+In the case of a locally submitted message in the &%acl_not_smtp%& ACL,
+the number of recipients is incremented by the &%$recipients_count%&
+for the entire message. Note that in either case the rate limiting
+engine will see a message with many recipients as a large high-speed
+burst.
The &%per_cmd%& option causes Exim to recompute the rate every time the
-condition is processed. This can be used to limit the SMTP command rate. The
-alias &%per_rcpt%& is provided for use in the RCPT ACL instead of &%per_cmd%&
-to make it clear that the effect is to limit the rate at which recipients are
-accepted. Note that in this case the rate limiting engine will see a message
-with many recipients as a large high-speed burst.
+condition is processed. This can be used to limit the SMTP command rate.
+This command is essentially an alias of &%per_rcpt%& to make it clear
+that the effect is to limit the rate at which individual commands,
+rather than recipients, are accepted.
+.section "Ratelimit options for handling fast clients" "ratophanfas"
If a client's average rate is greater than the maximum, the rate limiting
engine can react in two possible ways, depending on the presence of the
&%strict%& or &%leaky%& options. This is independent of the other
rest of the ACL. The default mode is leaky, which avoids a sender's
over-aggressive retry rate preventing it from getting any email through.
-The &%strict%& option means that the client's recorded rate is always updated.
-The effect of this is that Exim measures the client's average rate of attempts
-to send email, which can be much higher than the maximum. If the client is over
-the limit it will be subjected to counter-measures until it slows down below
-the maximum rate. The smoothing period determines the time it takes for a high
-sending rate to decay exponentially to 37% of its peak value, which means that
-you can work out the time (the number of smoothing periods) that a client is
-subjected to counter-measures after an over-limit burst with this formula:
-.code
-ln(peakrate/maxrate)
-.endd
-The &%leaky%& option means that the client's recorded rate is not updated if it
-is above the limit. The effect of this is that Exim measures the client's
-average rate of successfully sent email, which cannot be greater than the
-maximum. If the client is over the limit it may suffer some
+The &%strict%& option means that the client's recorded rate is always
+updated. The effect of this is that Exim measures the client's average rate
+of attempts to send email, which can be much higher than the maximum it is
+actually allowed. If the client is over the limit it may be subjected to
+counter-measures by the ACL until it slows down below the maximum rate. If
+the client stops attempting to send email for the time specified in the &'p'&
+parameter then its computed rate will decay exponentially to 37% of its peak
+value. You can work out the time (the number of smoothing periods) that a
+client is subjected to counter-measures after an over-limit burst with this
+formula:
+.code
+ ln(peakrate/maxrate)
+.endd
+The &%leaky%& (default) option means that the client's recorded rate is not
+updated if it is above the limit. The effect of this is that Exim measures the
+client's average rate of successfully sent email, which cannot be greater than
+the maximum allowed. If the client is over the limit it may suffer some
counter-measures (as specified in the ACL), but it will still be able to send
email at the configured maximum rate, whatever the rate of its attempts. This
is generally the better choice if you have clients that retry automatically.
+.section "Using rate limiting" "useratlim"
Exim's other ACL facilities are used to define what counter-measures are taken
when the rate limit is exceeded. This might be anything from logging a warning
(for example, while measuring existing sending rates in order to define
hints, the callout cache, and ratelimit data).
+.section "Reading ratelimit data without updating" "rearatdat"
+.cindex "rate limitint" "reading data without updating"
+If the &%noupdate%& option is present on a &%ratelimit%& ACL condition, Exim
+computes the rate and checks the limit as normal, but it does not update the
+saved data. This means that, in relevant ACLs, it is possible to lookup the
+existence of a specified (or auto-generated) ratelimit key without incrementing
+the ratelimit counter for that key. In order for this to be useful, another ACL
+entry must set the rate for the same key (otherwise it will always be zero).
+For example:
+.code
+acl_check_connect:
+ deny ratelimit = 100 / 5m / strict / per_cmd / noupdate
+ log_message = RATE: $sender_rate/$sender_rate_period \
+ (max $sender_rate_limit)
+.endd
+.display
+&'... some other logic and tests...'&
+.endd
+.code
+acl_check_mail:
+ warn ratelimit = 100 / 5m / strict / per_cmd
+ condition = ${if le{$sender_rate}{$sender_rate_limit}}
+ logwrite = RATE UPDATE: $sender_rate/$sender_rate_period \
+ (max $sender_rate_limit)
+.endd
+In this example, the rate is tested and used to deny access (when it is too
+high) in the connect ACL, but the actual computation of the remembered rate
+happens later, on a per-command basis, in another ACL.
+
+
+
.section "Address verification" "SECTaddressverification"
.cindex "verifying address" "options for"
.cindex "policy control" "address verification"
hosts, the ACL yields &"defer"&, unless the &%defer_ok%& parameter of the
&%callout%& option is given, in which case the condition is forced to succeed.
-.new
.cindex "SMTP" "output flushing, disabling for callout"
A callout may take a little time. For this reason, Exim normally flushes SMTP
output before performing a callout in an ACL, to avoid unexpected timeouts in
clients when the SMTP PIPELINING extension is in use. The flushing can be
disabled by using a &%control%& modifier to set &%no_callout_flush%&.
-.wen
timeout checks succeed. The &$prvscheck_result$& variable contains the result
of the checks (empty for failure, &"1"& for success).
-There are two more issues you must consider when implementing prvs-signing.
-Firstly, you need to ensure that prvs-signed addresses are not blocked by your
-ACLs. A prvs-signed address contains a slash character, but the default Exim
-configuration contains this statement in the RCPT ACL:
-.code
-deny message = Restricted characters in address
- domains = +local_domains
- local_parts = ^[.] : ^.*[@%!/|]
-.endd
-This is a conservative rule that blocks local parts that contain slashes. You
-should remove the slash in the last line.
-
-Secondly, you have to ensure that the routers accept prvs-signed addresses and
+There is one more issue you must consider when implementing prvs-signing:
+you have to ensure that the routers accept prvs-signed addresses and
deliver them correctly. The easiest way to handle this is to use a &(redirect)&
router to remove the signature with a configuration along these lines:
.code
.code
av_scanner = sophie:/var/run/sophie
.endd
-If the value of &%av_scanner%& starts with dollar character, it is expanded
+If the value of &%av_scanner%& starts with a dollar character, it is expanded
before use. The following scanner types are supported in this release:
.vlist
number, and a port, separated by space, as in the second of these examples:
.code
av_scanner = clamd:/opt/clamd/socket
-av_scanner = clamd:192.168.2.100 1234
-.endd
+av_scanner = clamd:192.0.2.3 1234
+av_scanner = clamd:192.0.2.3 1234:local
+.endd
+If the value of av_scanner points to a UNIX socket file or contains the local
+keyword, then the ClamAV interface will pass a filename containing the data
+to be scanned, which will should normally result in less I/O happening and be
+more efficient. Normally in the TCP case, the data is streamed to ClamAV as
+Exim does not assume that there is a common filesystem with the remote host.
+There is an option WITH_OLD_CLAMAV_STREAM in &_src/EDITME_& available, should
+you be running a version of ClamAV prior to 0.95.
If the option is unset, the default is &_/tmp/clamd_&. Thanks to David Saez for
contributing the code for this scanner.
use the &%demime%& condition (see section &<<SECTdemimecond>>&) before the
&%malware%& condition.
+.new
+Beware the interaction of Exim's &%message_size_limit%& with any size limits
+imposed by your anti-virus scanner.
+.wen
+
Here is a very simple scanning example:
.code
deny message = This message contains malware ($malware_name)
&*Warning*&: It is not possible to use the UNIX socket connection method with
multiple &%spamd%& servers.
+The &%spamd_address%& variable is expanded before use if it starts with
+a dollar sign. In this case, the expansion may return a string that is
+used as the list so that multiple spamd servers can be the result of an
+expansion.
.section "Calling SpamAssassin from an Exim ACL" "SECID206"
Here is a simple example of the use of the &%spam%& condition in a DATA ACL:
&%spam%& condition for its side effects (see the variables below), you can make
it always return &"true"& by appending &`:true`& to the username.
+.new
.cindex "spam scanning" "returned variables"
When the &%spam%& condition is run, it sets up a number of expansion
-variables. With the exception of &$spam_score_int$&, these are usable only
-within ACLs; their values are not retained with the message and so cannot be
-used at delivery time.
+variables. These variables are saved with the received message, thus they are
+available for use at delivery time.
+.wen
.vlist
.vitem &$spam_score$&
.vitem &$spam_score_int$&
The spam score of the message, multiplied by ten, as an integer value. For
-example &"34"& or &"305"&. This is useful for numeric comparisons in
-conditions. This variable is special; its value is saved with the message, and
-written to Exim's spool file. This means that it can be used during the whole
-life of the message on your Exim system, in particular, in routers or
-transports during the later delivery phase.
+example &"34"& or &"305"&. It may appear to disagree with &$spam_score$&
+because &$spam_score$& is rounded and &$spam_score_int$& is truncated.
+The integer value is useful for numeric comparisons in conditions.
+
.vitem &$spam_bar$&
A string consisting of a number of &"+"& or &"-"& characters, representing the
message. Useful for inclusion in headers or reject messages.
.endlist
-The &%spam%& condition caches its results. If you call it again with the same
-user name, it does not scan again, but rather returns the same values as
-before.
+The &%spam%& condition caches its results unless expansion in
+spamd_address was used. If you call it again with the same user name, it
+does not scan again, but rather returns the same values as before.
-The &%spam%& condition returns DEFER if there is any error while running the
-message through SpamAssassin. If you want to treat DEFER as FAIL (to pass on to
-the next ACL statement block), append &`/defer_ok`& to the right-hand side of
-the spam condition, like this:
+The &%spam%& condition returns DEFER if there is any error while running
+the message through SpamAssassin or if the expansion of spamd_address
+failed. If you want to treat DEFER as FAIL (to pass on to the next ACL
+statement block), append &`/defer_ok`& to the right-hand side of the
+spam condition, like this:
.code
deny message = This message was classified as SPAM
spam = joe/defer_ok
options may both refer to the same ACL if you want the same processing in both
cases.
-These ACLs are called (possibly many times) just before the
-&%acl_smtp_data%& ACL in the case of an SMTP message, or just before the
-&%acl_not_smtp%& ACL in the case of a non-SMTP message. However, a MIME ACL
-is called only if the message contains a &'MIME-Version:'& header line. When a
-call to a MIME ACL does not yield &"accept"&, ACL processing is aborted and the
-appropriate result code is sent to the client. In the case of an SMTP message,
-the &%acl_smtp_data%& ACL is not called when this happens.
+These ACLs are called (possibly many times) just before the &%acl_smtp_data%&
+ACL in the case of an SMTP message, or just before the &%acl_not_smtp%& ACL in
+the case of a non-SMTP message. However, a MIME ACL is called only if the
+message contains a &'Content-Type:'& header line. When a call to a MIME
+ACL does not yield &"accept"&, ACL processing is aborted and the appropriate
+result code is sent to the client. In the case of an SMTP message, the
+&%acl_smtp_data%& ACL is not called when this happens.
You cannot use the &%malware%& or &%spam%& conditions in a MIME ACL; these can
only be used in the DATA or non-SMTP ACLs. However, you can use the &%regex%&
If the string does not start with a slash, it is used as the
filename, and the default path is then used.
.endlist
-&new("The &%decode%& condition normally succeeds. It is only false for syntax
-errors or unusual circumstances such as memory shortages.")
-You can easily decode a file with its original, proposed filename using
+The &%decode%& condition normally succeeds. It is only false for syntax
+errors or unusual circumstances such as memory shortages. You can easily decode
+a file with its original, proposed filename using
.code
decode = $mime_filename
.endd
.cindex "&[local_scan()]& function" "available Exim variables"
The header &_local_scan.h_& gives you access to a number of C variables. These
are the only ones that are guaranteed to be maintained from release to release.
-Note, however, that you can obtain the value of any Exim variable,
-&new("including &$recipients$&,") by calling &'expand_string()'&. The exported
-variables are as follows:
+Note, however, that you can obtain the value of any Exim expansion variable,
+including &$recipients$&, by calling &'expand_string()'&. The exported
+C variables are as follows:
.vlist
+.vitem &*int&~body_linecount*&
+This variable contains the number of lines in the message's body.
+
+.vitem &*int&~body_zerocount*&
+This variable contains the number of binary zero bytes in the message's body.
+
.vitem &*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
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
+of the &%max_rcpt%&s option in the &(smtp)& transport allows, in which case
+they are split into groups containing no more than &%max_rcpt%&s 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.
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.
+Minimal policy checking is done for BSMTP input. Only the non-SMTP
+ACL is run in the same way as for 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
No retry data is maintained, and any retry rules are ignored.
.next
A number of Exim options are overridden: &%deliver_drop_privilege%& is forced
-true, &%max_rcpt%& in the smtp transport is forced to &"unlimited"&,
+true, &%max_rcpt%& in the &(smtp)& transport is forced to &"unlimited"&,
&%remote_max_parallel%& is forced to one, and fallback hosts are ignored.
.endlist
.endd
.endlist
-.new
.cindex "log" "process ids in"
.cindex "pid (process id)" "in log lines"
Exim does not include its process id in log lines by default, but you can
request that it does so by specifying the &`pid`& log selector (see section
&<<SECTlogselector>>&). When this is set, the process id is output, in square
brackets, immediately after the time and date.
-.wen
.display
&`A `& authenticator name (and optional id)
&`C `& SMTP confirmation on delivery
-.new
&` `& command list for &"no mail in SMTP session"&
-.wen
&`CV `& certificate verification status
-.new
&`D `& duration of &"no mail in SMTP session"&
-.wen
&`DN `& distinguished name from peer certificate
&`DT `& on &`=>`& lines: time taken for a delivery
&`F `& sender address (on delivery lines)
&`*queue_run `& start and end queue runs
&` queue_time `& time on queue for one recipient
&` queue_time_overall `& time on queue for whole message
-.new
&` pid `& Exim process id
-.wen
&` received_recipients `& recipients on <= lines
&` received_sender `& sender on <= lines
&`*rejected_header `& header contents on reject log
&` smtp_confirmation `& SMTP confirmation on => lines
&` smtp_connection `& SMTP connections
&` smtp_incomplete_transaction`& incomplete SMTP transactions
-.new
&` smtp_no_mail `& session with no MAIL commands
-.wen
&` smtp_protocol_error `& SMTP protocol errors
&` smtp_syntax_error `& SMTP syntax errors
&` subject `& contents of &'Subject:'& on <= lines
the default setting, because for most ordinary configurations, the remote port
number is always 25 (the SMTP port).
.next
-.new
.cindex "log" "process ids in"
.cindex "pid (process id)" "in log lines"
&%pid%&: The current process id is added to every log line, in square brackets,
immediately after the time and date.
-.wen
.next
.cindex "log" "queue run"
.cindex "queue runner" "logging"
and the message sender plus any accepted recipients are included in the log
line. This can provide evidence of dictionary attacks.
.next
-.new
.cindex "log" "non-MAIL SMTP sessions"
.cindex "MAIL" "logging session without"
&%smtp_no_mail%&: A line is written to the main log whenever an accepted SMTP
the last 20 are listed, preceded by &"..."&. However, with the default
setting of 10 for &%smtp_accep_max_nonmail%&, the connection will in any case
have been aborted before 20 non-mail commands are processed.
-.wen
.next
.cindex "log" "SMTP protocol error"
.cindex "SMTP" "logging protocol error"
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.
The input files can be in Exim log format or syslog format.
-.new
If a matching log line is not associated with a specific message, it is
included in &'exigrep'&'s output without any additional lines. The usage is:
.display
The &%-v%& option inverts the matching condition. That is, a line is selected
if it does &'not'& match the pattern.
-.wen
If the location of a &'zcat'& command is known from the definition of
ZCAT_COMMAND in &_Local/Makefile_&, &'exigrep'& automatically passes any file
into the Exim account from running a privileged Exim with an arbitrary
configuration file, and using it to break into other accounts.
.next
-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.
+.new
+If a non-trusted configuration file (i.e. not the default configuration file
+or one which is trusted by virtue of being listed in the TRUSTED_CONFIG_LIST
+file) is specified with &%-C%&, or if macros are given with &%-D%& (but see
+the next item), then root privilege is retained only if the caller of Exim is
+root. This 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.
+.wen
+.next
+The WHITELIST_D_MACROS build option declares some macros to be safe to override
+with &%-D%& if the real uid is one of root, the Exim run-time user or the
+CONFIGURE_OWNER, if defined. The potential impact of this option is limited by
+requiring the run-time value supplied to &%-D%& to match a regex that errs on
+the restrictive side. Requiring build-time selection of safe macros is onerous
+but this option is intended solely as a transition mechanism to permit
+previously-working configurations to continue to work after release 4.73.
.next
If DISABLE_D_OPTION is defined, the use of the &%-D%& command line option
is disabled.
.oindex "&%-D%&"
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.
+calling process is not running as root, the uid and gid are changed to those of
+the calling process.
+However, if DISABLE_D_OPTION is defined in &_Local/Makefile_&, the &%-D%&
+option may not be used at all.
+If WHITELIST_D_MACROS is defined in &_Local/Makefile_&, then some macro values
+can be supplied if the calling process is running as root, the Exim run-time
+user or CONFIGURE_OWNER, if defined.
.next
.oindex "&%-be%&"
.oindex "&%-bf%&"
+.section "Dynamic module directory" "SECTdynmoddir"
+Any dynamically loadable modules must be installed into the directory
+defined in &`LOOKUP_MODULE_DIR`& in &_Local/Makefile_& for Exim to permit
+loading it.
+
+
+
.section "Use of sprintf()" "SECID279"
.cindex "&[sprintf()]&"
A large number of occurrences of &"sprintf"& in the code are actually calls to
If the message is cryptographically signed, any change will invalidate the
signature.
.endlist
-.new
All in all, modifying -D files is fraught with danger.
-.wen
-.new
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
file remains in existence. When Exim next processes the message, it notices the
-J file and uses it to update the -H file before starting the next delivery
attempt.
-.wen
.section "Format of the -H file" "SECID282"
.cindex "uid (user 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 &new("via the daemon"), it is
+message. For a message received over TCP/IP via the daemon, it is
normally the Exim user.
The third line of the file contains the address of the message's sender as
.ecindex IIDforspo2
.ecindex IIDforspo3
+. ////////////////////////////////////////////////////////////////////////////
+. ////////////////////////////////////////////////////////////////////////////
+
+.chapter "Support for DKIM (DomainKeys Identified Mail) - RFC4871" "CHID12" &&&
+ "DKIM Support"
+.cindex "DKIM"
+
+Since version 4.70, DKIM support is compiled into Exim by default. It can be
+disabled by setting DISABLE_DKIM=yes in Local/Makefile.
+
+Exim's DKIM implementation allows to
+.olist
+Sign outgoing messages: This function is implemented in the SMTP transport.
+It can co-exist with all other Exim features, including transport filters.
+.next
+Verify signatures in incoming messages: This is implemented by an additional
+ACL (acl_smtp_dkim), which can be called several times per message, with
+different signature contexts.
+.endlist
+
+In typical Exim style, the verification implementation does not include any
+default "policy". Instead it enables you to build your own policy using
+Exim's standard controls.
+Please note that verification of DKIM signatures in incoming mail is turned
+on by default for logging purposes. For each signature in incoming email,
+exim will log a line displaying the most important signature details, and the
+signature status. Here is an example:
+.code
+2009-09-09 10:22:28 1MlIRf-0003LU-U3 DKIM: d=facebookmail.com s=q1-2009b c=relaxed/relaxed a=rsa-sha1 i=@facebookmail.com t=1252484542 [verification succeeded]
+.endd
+You might want to turn off DKIM verification processing entirely for internal
+or relay mail sources. To do that, set the &%dkim_disable_verify%& ACL
+control modifier. This should typically be done in the RCPT ACL, at points
+where you accept mail from relay sources (internal hosts or authenticated
+senders).
+
+
+.section "Signing outgoing messages" "SECID513"
+.cindex "DKIM" "signing"
+
+Signing is implemented by setting private options on the SMTP transport.
+These options take (expandable) strings as arguments.
+
+.option dkim_domain smtp string&!! unset
+MANDATORY:
+The domain you want to sign with. The result of this expanded
+option is put into the &%$dkim_domain%& expansion variable.
+
+.option dkim_selector smtp string&!! unset
+MANDATORY:
+This sets the key selector string. You can use the &%$dkim_domain%& expansion
+variable to look up a matching selector. The result is put in the expansion
+variable &%$dkim_selector%& which should be used in the &%dkim_private_key%&
+option along with &%$dkim_domain%&.
+
+.option dkim_private_key smtp string&!! unset
+MANDATORY:
+This sets the private key to use. You can use the &%$dkim_domain%& and
+&%$dkim_selector%& expansion variables to determine the private key to use.
+The result can either
+.ilist
+be a valid RSA private key in ASCII armor, including line breaks.
+.next
+start with a slash, in which case it is treated as a file that contains
+the private key.
+.next
+be "0", "false" or the empty string, in which case the message will not
+be signed. This case will not result in an error, even if &%dkim_strict%&
+is set.
+.endlist
+
+.option dkim_canon smtp string&!! unset
+OPTIONAL:
+This option sets the canonicalization method used when signing a message.
+The DKIM RFC currently supports two methods: "simple" and "relaxed".
+The option defaults to "relaxed" when unset. Note: the current implementation
+only supports using the same canonicalization method for both headers and body.
+
+.option dkim_strict smtp string&!! unset
+OPTIONAL:
+This option defines how Exim behaves when signing a message that
+should be signed fails for some reason. When the expansion evaluates to
+either "1" or "true", Exim will defer. Otherwise Exim will send the message
+unsigned. You can use the &%$dkim_domain%& and &%$dkim_selector%& expansion
+variables here.
+
+.option dkim_sign_headers smtp string&!! unset
+OPTIONAL:
+When set, this option must expand to (or be specified as) a colon-separated
+list of header names. Headers with these names will be included in the message
+signature. When unspecified, the header names recommended in RFC4871 will be
+used.
+
+
+.section "Verifying DKIM signatures in incoming mail" "SECID514"
+.cindex "DKIM" "verification"
+
+Verification of DKIM signatures in incoming email is implemented via the
+&%acl_smtp_dkim%& ACL. By default, this ACL is called once for each
+syntactically(!) correct signature in the incoming message.
+
+To evaluate the signature in the ACL a large number of expansion variables
+containing the signature status and its details are set up during the
+runtime of the ACL.
+
+Calling the ACL only for existing signatures is not sufficient to build
+more advanced policies. For that reason, the global option
+&%dkim_verify_signers%&, and a global expansion variable
+&%$dkim_signers%& exist.
+
+The global option &%dkim_verify_signers%& can be set to a colon-separated
+list of DKIM domains or identities for which the ACL &%acl_smtp_dkim%& is
+called. It is expanded when the message has been received. At this point,
+the expansion variable &%$dkim_signers%& already contains a colon-separated
+list of signer domains and identities for the message. When
+&%dkim_verify_signers%& is not specified in the main configuration,
+it defaults as:
+.code
+dkim_verify_signers = $dkim_signers
+.endd
+This leads to the default behaviour of calling &%acl_smtp_dkim%& for each
+DKIM signature in the message. Current DKIM verifiers may want to explicitly
+call the ACL for known domains or identities. This would be achieved as follows:
+.code
+dkim_verify_signers = paypal.com:ebay.com:$dkim_signers
+.endd
+This would result in &%acl_smtp_dkim%& always being called for "paypal.com"
+and "ebay.com", plus all domains and identities that have signatures in the message.
+You can also be more creative in constructing your policy. For example:
+.code
+dkim_verify_signers = $sender_address_domain:$dkim_signers
+.endd
+
+If a domain or identity is listed several times in the (expanded) value of
+&%dkim_verify_signers%&, the ACL is only called once for that domain or identity.
+Inside the &%acl_smtp_dkim%&, the following expansion variables are
+available (from most to least important):
+
+.vlist
+.vitem &%$dkim_cur_signer%&
+The signer that is being evaluated in this ACL run. This can be a domain or
+an identity. This is one of the list items from the expanded main option
+&%dkim_verify_signers%& (see above).
+.vitem &%$dkim_verify_status%&
+A string describing the general status of the signature. One of
+.ilist
+&%none%&: There is no signature in the message for the current domain or
+identity (as reflected by &%$dkim_cur_signer%&).
+.next
+&%invalid%&: The signature could not be verified due to a processing error.
+More detail is available in &%$dkim_verify_reason%&.
+.next
+&%fail%&: Verification of the signature failed. More detail is
+available in &%$dkim_verify_reason%&.
+.next
+&%pass%&: The signature passed verification. It is valid.
+.endlist
+.vitem &%$dkim_verify_reason%&
+A string giving a litte bit more detail when &%$dkim_verify_status%& is either
+"fail" or "invalid". One of
+.ilist
+&%pubkey_unavailable%& (when &%$dkim_verify_status%&="invalid"): The public
+key for the domain could not be retrieved. This may be a temporary problem.
+.next
+&%pubkey_syntax%& (when &%$dkim_verify_status%&="invalid"): The public key
+record for the domain is syntactically invalid.
+.next
+&%bodyhash_mismatch%& (when &%$dkim_verify_status%&="fail"): The calculated
+body hash does not match the one specified in the signature header. This
+means that the message body was modified in transit.
+.next
+&%signature_incorrect%& (when &%$dkim_verify_status%&="fail"): The signature
+could not be verified. This may mean that headers were modified,
+re-written or otherwise changed in a way which is incompatible with
+DKIM verification. It may of course also mean that the signature is forged.
+.endlist
+.vitem &%$dkim_domain%&
+The signing domain. IMPORTANT: This variable is only populated if there is
+an actual signature in the message for the current domain or identity (as
+reflected by &%$dkim_cur_signer%&).
+.vitem &%$dkim_identity%&
+The signing identity, if present. IMPORTANT: This variable is only populated
+if there is an actual signature in the message for the current domain or
+identity (as reflected by &%$dkim_cur_signer%&).
+.vitem &%$dkim_selector%&
+The key record selector string.
+.vitem &%$dkim_algo%&
+The algorithm used. One of 'rsa-sha1' or 'rsa-sha256'.
+.vitem &%$dkim_canon_body%&
+The body canonicalization method. One of 'relaxed' or 'simple'.
+.vitem &%dkim_canon_headers%&
+The header canonicalization method. One of 'relaxed' or 'simple'.
+.vitem &%$dkim_copiedheaders%&
+A transcript of headers and their values which are included in the signature
+(copied from the 'z=' tag of the signature).
+.vitem &%$dkim_bodylength%&
+The number of signed body bytes. If zero ("0"), the body is unsigned. If no
+limit was set by the signer, "9999999999999" is returned. This makes sure
+that this variable always expands to an integer value.
+.vitem &%$dkim_created%&
+UNIX timestamp reflecting the date and time when the signature was created.
+When this was not specified by the signer, "0" is returned.
+.vitem &%$dkim_expires%&
+UNIX timestamp reflecting the date and time when the signer wants the
+signature to be treated as "expired". When this was not specified by the
+signer, "9999999999999" is returned. This makes it possible to do useful
+integer size comparisons against this value.
+.vitem &%$dkim_headernames%&
+A colon-separated list of names of headers included in the signature.
+.vitem &%$dkim_key_testing%&
+"1" if the key record has the "testing" flag set, "0" if not.
+.vitem &%$dkim_key_nosubdomaining%&
+"1" if the key record forbids subdomaining, "0" otherwise.
+.vitem &%$dkim_key_srvtype%&
+Service type (tag s=) from the key record. Defaults to "*" if not specified
+in the key record.
+.vitem &%$dkim_key_granularity%&
+Key granularity (tag g=) from the key record. Defaults to "*" if not specified
+in the key record.
+.vitem &%$dkim_key_notes%&
+Notes from the key record (tag n=).
+.endlist
+
+In addition, two ACL conditions are provided:
+
+.vlist
+.vitem &%dkim_signers%&
+ACL condition that checks a colon-separated list of domains or identities
+for a match against the domain or identity that the ACL is currently verifying
+(reflected by &%$dkim_cur_signer%&). This is typically used to restrict an ACL
+verb to a group of domains or identities. For example:
+
+.code
+# Warn when message apparently from GMail has no signature at all
+warn log_message = GMail sender without DKIM signature
+ sender_domains = gmail.com
+ dkim_signers = gmail.com
+ dkim_status = none
+.endd
+
+.vitem &%dkim_status%&
+ACL condition that checks a colon-separated list of possible DKIM verification
+results agains the actual result of verification. This is typically used
+to restrict an ACL verb to a list of verification outcomes, like:
+
+.code
+deny message = Message from Paypal with invalid or missing signature
+ sender_domains = paypal.com:paypal.de
+ dkim_signers = paypal.com:paypal.de
+ dkim_status = none:invalid:fail
+.endd
+
+The possible status keywords are: 'none','invalid','fail' and 'pass'. Please
+see the documentation of the &%$dkim_verify_status%& expansion variable above
+for more information of what they mean.
+.endlist
+
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
-.chapter "Adding new drivers or lookup types" "CHID12" &&&
+.chapter "Adding new drivers or lookup types" "CHID13" &&&
"Adding drivers or lookups"
.cindex "adding drivers"
.cindex "new drivers, adding"
git://git.exim.org / exim.git / blobdiff