-. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.25 2007/10/18 12:08:46 nm4 Exp $
+. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.55 2009/10/14 14:48:40 nm4 Exp $
.
. /////////////////////////////////////////////////////////////////////////////
. This is the primary source of the Exim Manual. It is an xfpt document that is
. the <bookinfo> element must also be updated for each new edition.
. /////////////////////////////////////////////////////////////////////////////
-.set previousversion "4.67"
-.set version "4.68"
+.set previousversion "4.69"
+.set version "4.70"
.set ACL "access control lists (ACLs)"
.set I " "
<bookinfo>
<title>Specification of the Exim Mail Transfer Agent</title>
<titleabbrev>The Exim MTA</titleabbrev>
-<date>23 August 2007</date>
+<date>09 June 2009</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>
<revhistory><revision>
- <revnumber>4.68</revnumber>
- <date>23 August 2007</date>
+ <revnumber>4.70</revnumber>
+ <date>10 June 2009</date>
<authorinitials>PH</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
.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.
.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 "FAQ"
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 &new("(&url(http://wiki.exim.org))"),
+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 &new("&url(http://bugs.exim.org)"). 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.
lists.
.section "Exim training" "SECID4"
-.new
.cindex "training courses"
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/).
-.wen
.section "Bug reports" "SECID5"
.cindex "bug reports"
.cindex "reporting bugs"
-Reports of obvious bugs &new("can be emailed to &'bugs@exim.org'& or reported
-via the Bugzilla (&url(http://bugs.exim.org)).") However, if you are unsure
+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"
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"
.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.
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.
-.new
.vitem &%-Mvc%&&~<&'message&~id'&>
.oindex "&%-Mvc%&"
.cindex "message" "listing 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.
-.wen
.vitem &%-Mvh%&&~<&'message&~id'&>
.oindex "&%-Mvh%&"
define mechanisms for copying messages to destinations (see chapters
&<<CHAPtransportgeneric>>&&--&<<CHAPsmtptrans>>&).
.next
-.new
&'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>>&.
-.wen
.next
&'rewrite'&: Global address rewriting rules, for use when a message arrives and
when new addresses are generated during delivery. Rewriting is discussed 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
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.
-.new
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.
-.wen
.section "Rewriting configuration" "SECID58"
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 &$2$&.
-
-
-
-
-
-
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
utility program for creating DBM files (&'exim_dbmbuild'&) includes the zeros
by default, but has an option to omit them (see section &<<SECTdbmbuild>>&).
.next
-.new
.cindex "lookup" "dsearch"
.cindex "dsearch lookup type"
&(dsearch)&: The given file must be a directory; this is searched for an entry
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>>&.
-.wen
.next
.cindex "lookup" "iplsearch"
.cindex "iplsearch lookup type"
&%mysql_servers%&, &%pgsql_servers%&, &%oracle_servers%&, or &%ibase_servers%&
option (as appropriate) must be set to a colon-separated list of server
information.
-&new("(For MySQL and PostgreSQL only, the global option need not be set if all
+(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
+&<<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:
hide mysql_servers = localhost/users/root/secret:\
otherhost/users/root/othersecret
.endd
-.new
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 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.
-.wen
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.
-.new
.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
.endd
In an updating lookup, you could then write:
.code
-${lookup mysql{servers=master; UPDATE ...}
+${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
-${lookup pgsql{servers=master/db/name/pw; UPDATE ...}
+${lookup pgsql{servers=master/db/name/pw; UPDATE ...} }
.endd
-.wen
.section "Special MySQL features" "SECID73"
possible to use the same configuration file on several different hosts that
differ only in their names.
.next
-.new
.cindex "@[] in a domain list"
.cindex "domain list" "matching local IP interfaces"
.cindex "domain literal"
&%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.
-.wen
.next
.cindex "@mx_any"
.cindex "@mx_primary"
&'cipher.key.ex'&.
.next
-.new
.cindex "regular expressions" "in domain list"
.cindex "domain list" "matching regular expression"
If a pattern starts with a circumflex character, it is treated as a regular
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>>&.
-.wen
&*Warning*&: Because domain lists are expanded before being processed, you
must escape any backslash and dollar characters in the regular expression, or
is 192.168.34.6, the key that is looked up for the above example is
&"192.168.34.0/24"&.
-.new
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
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.
-.wen
&*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
requirement. Other kinds of wildcarding require the use of a regular
expression.
.next
-.new
.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
case-dependent by starting it with &`(?-i)`&. References to descriptions of the
syntax of regular expressions are given in chapter &<<CHAPregexp>>&. For
example,
-.wen
.code
^(a|b)\.c\.d$
.endd
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.
-.new
&*Note*&: This section applies to permanent lookup failures. It does &'not'&
apply to temporary DNS errors, whose handling is described in the next section.
-.wen
.cindex "&`+include_unknown`&"
.cindex "&`+ignore_unknown`&"
list.
-.new
.section "Temporary DNS errors when looking up host information" &&&
"SECTtemdnserr"
.cindex "host" "lookup failures, temporary"
&`+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.
-.wen
character set defined by &%headers_charset%&. Overlong RFC 2047 &"words"& are
not recognized unless &%check_rfc2047_length%& is set false.
-.new
&*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.
-.wen
As a special case, the numerical value of an empty string is taken as
zero.
+.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 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
+
.vitem &*crypteq&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*&
.cindex "expansion" "encrypted comparison"
.cindex "encrypted strings, comparing"
an IP address. Both IPv4 and IPv6 addresses are valid for &%isip%&, whereas
&%isip4%& and &%isip6%& test specifically for IPv4 or IPv6 addresses.
-.new
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
${if isip4{$sender_host_address}...
.endd
to test which IP version an incoming SMTP connection is using.
-.wen
.vitem &*ldapauth&~{*&<&'ldap&~query'&>&*}*&
.cindex "LDAP" "use for authentication"
content-scanning extension and the obsolete &%demime%& condition. For details,
see section &<<SECTdemimecond>>&.
-.new
.vitem &$dnslist_domain$& &&&
&$dnslist_matched$& &&&
&$dnslist_text$& &&&
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.
-.wen
.vitem &$domain$&
.vindex "&$domain$&"
.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.
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>>&).
-.new
.vitem &$max_received_linelength$&
.vindex "&$max_received_linelength$&"
.cindex "maximum" "line length"
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).
-.wen
.vitem &$message_age$&
.cindex "message" "age of"
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.
-.new
.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.
-.wen
.vitem &$message_body_end$&
.cindex "body of message" "expansion variable"
message was received, and &"0"& otherwise.
.vitem &$tls_cipher$&
-.new
.vindex "&$tls_cipher$&"
When a message is received from a remote host over an encrypted SMTP
connection, this variable is set to the cipher suite that was negotiated, for
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.
-.wen
.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. &new("Like &$tls_cipher$&, the
+&$tls_peerdn$& during subsequent processing. Like &$tls_cipher$&, the
value is retained during message delivery, except during outbound SMTP
-deliveries.")
+deliveries.
.vitem &$tod_bsdinbox$&
.vindex "&$tod_bsdinbox$&"
.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 &new(&%message_body_newlines%&) "retain newlines in &$message_body$&"
+.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 &new(&%ibase_servers%&) "InterBase servers"
+.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 &new(&%mysql_servers%&) "default MySQL servers"
-.row &new(&%oracle_servers%&) "Oracle servers"
-.row &new(&%pgsql_servers%&) "default PostgreSQL servers"
+.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 &new(&%queue_only_load_latch%&) "don't re-evaluate load for each message"
+.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 &%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 &new(&%queue_only_load_latch%&) "don't re-evaluate load for each message"
+.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"
(?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. &new(Slashes) 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
interfaces and recognizing the local host.
-.new
.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.
-.wen
an argument that is longer behaves as if &[getpwnam()]& failed.
-.new
.option message_body_newlines main bool false
.cindex "message body" "newlines in variables"
.cindex "newline" "in message body variables"
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.
-.wen
.option message_body_visible main integer 500
.option queue_only_load main fixed-point unset
-.new
.cindex "load average"
.cindex "queueing incoming messages"
.cindex "message" "queueing by load"
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.
-.wen
Deliveries will subsequently be performed by queue runner processes. This
option has no effect on ancient operating systems on which Exim cannot
&%smtp_load_reserve%&.
-.new
.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
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.
-.wen
.option queue_only_override main boolean true
.option smtp_accept_queue main integer 0
-.new
.cindex "SMTP" "incoming connection count"
.cindex "queueing incoming messages"
.cindex "message" "queueing by SMTP connection count"
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.
-.wen
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
either &%tls_verify_hosts%& or &%tls_try_verify_hosts%& is set and
&%tls_verify_certificates%& is not set.
-.new
Any client that matches &%tls_verify_hosts%& is constrained by
&%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
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.
-.wen
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
check_local_user
transport = local_delivery
.endd
-.new
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
-.wen
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
.option pass_router routers string unset
-.new
.cindex "router" "go to after &""pass""&"
Routers that recognize the generic &%self%& option (&(dnslookup)&,
&(ipliteral)&, and &(manualroute)&) are able to return &"pass"&, forcing
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"& because it cannot handle an address.
-.wen
local_part_prefix = real-
transport = local_delivery
.endd
-.new
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
-.wen
.option syntax_errors_text redirect string&!! unset
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
-.new
&*Note:*& If you set &%use_crlf%& true, you must change any occurrences of
&`\n`& to &`\r\n`& in &%message_prefix%&.
-.wen
.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
-.new
&*Note:*& If you set &%use_crlf%& true, you must change any occurrences of
&`\n`& to &`\r\n`& in &%message_suffix%&.
-.wen
.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.
-.new
&*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.
-.wen
.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. &new("Delivery
-is deferred, and will be tried again later.") Here is an example of a typical
+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:
.code
message_prefix =
.endd
-.new
&*Note:*& If you set &%use_crlf%& true, you must change any occurrences of
&`\n`& to &`\r\n`& in &%message_prefix%&.
-.wen
.option message_suffix pipe string&!! "see below"
.code
message_suffix =
.endd
-.new
&*Note:*& If you set &%use_crlf%& true, you must change any occurrences of
&`\n`& to &`\r\n`& in &%message_suffix%&.
-.wen
.option path pipe string "see below"
of batched SMTP, the byte sequence written to the pipe is then an exact image
of what would be sent down a real SMTP connection.
-.new
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. 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.
-.wen
.option use_shell pipe boolean false
&%serialize_hosts%&, and the various TLS options are expanded.
-.new
.section "Use of $tls_cipher and $tls_peerdn" "usecippeer"
.vindex &$tls_cipher$&
.vindex &$tls_peerdn$&
appropriate values for the outgoing connection, and these are the values that
are in force when any authenticators are run and when the
&%authenticated_sender%& option is expanded.
-.wen
.section "Private options for smtp" "SECID146"
to be deferred. If the result of expansion is an empty string, that is also
ignored.
-.new
The expansion happens after the outgoing connection has been made and TLS
started, if required. This means that the &$host$&, &$host_address$&,
&$tls_cipher$&, and &$tls_peerdn$& variables are set according to the
particular connection.
-.wen
If the SMTP session is not authenticated, the expansion of
&%authenticated_sender%& still happens (and can cause the delivery to be
.vindex "&$host$&"
.vindex "&$host_address$&"
This option specifies which interface to bind to when making an outgoing SMTP
-call. &new("The value is an IP address, not an interface name such as
-&`eth0`&.") Do not confuse this with the interface address that was used when a
+call. The value is an IP address, not an interface name such as
+&`eth0`&. Do not confuse this with the interface address that was used when a
message was received, which is in &$received_ip_address$&, formerly known as
&$interface_address$&. The name was changed to minimize confusion with the
outgoing interface address. There is no variable that contains an outgoing
&`s`& rewrite the &'Sender:'& header
&`t`& rewrite the &'To:'& header
.endd
+"All headers" means all of the headers listed above that can be selected
+individually, plus their &'Resent-'& versions. It does not include
+other headers such as &'Subject:'& etc.
+
You should be particularly careful about rewriting &'Sender:'& headers, and
restrict this to special known cases in your own domains.
.chapter "Retry configuration" "CHAPretry"
.scindex IIDretconf1 "retry" "configuration, description of"
.scindex IIDregconf2 "configuration file" "retry section"
-.new
The &"retry"& section of the runtime configuration file contains a list of
retry rules that control how often Exim tries to deliver messages that cannot
be delivered at the first attempt. If there are no retry rules (the section is
general-purpose retry rule (see section &<<SECID57>>&). The &%-brt%& command
line option can be used to test which retry rule will be used for a given
address, domain and error.
-.wen
The most common cause of retries is temporary failure to deliver to a remote
host because the host is down, or inaccessible because of a network problem.
.cindex "authentication" "generic options"
.cindex "options" "generic; for authenticators"
-.new
.option client_condition authenticators string&!! unset
When Exim is authenticating as a client, it skips any authenticator whose
&%client_condition%& expansion yields &"0"&, &"no"&, or &"false"&. This can be
(Older documentation incorrectly states that &$tls_cipher$& contains the cipher
used for incoming messages. In fact, during SMTP delivery, it contains the
cipher used for the delivery.)
-.wen
.option driver authenticators string unset
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=$auth1,ou=people,o=example.org
.endd
-Note the use of the &%quote_ldap_dn%& operator to correctly quote the DN for
-authentication. However, the basic &%quote%& operator, rather than any of the
-LDAP quoting operators, is the correct one to use for the password, because
-quoting is needed only to make the password conform to the Exim syntax. At the
-LDAP level, the password is an uninterpreted string.
+We have to check that the username is not empty before using it, because LDAP
+does not permit empty DN components. We must also use the &%quote_ldap_dn%&
+operator to correctly quote the DN for authentication. However, the basic
+&%quote%& operator, rather than any of the LDAP quoting operators, is the
+correct one to use for the password, because quoting is needed only to make
+the password conform to the Exim syntax. At the LDAP level, the password is an
+uninterpreted string.
.section "GnuTLS parameter computation" "SECID181"
-GnuTLS uses RSA and D-H parameters that may take a substantial amount of time
+GnuTLS uses D-H parameters that may take a substantial amount of time
to compute. It is unreasonable to re-compute them for every TLS session.
Therefore, Exim keeps this data in a file in its spool directory, called
&_gnutls-params_&. The file is owned by the Exim user and is readable only by
-its owner. Every Exim process that start up GnuTLS reads the RSA and D-H
+its owner. Every Exim process that start up GnuTLS reads the D-H
parameters from this file. If the file does not exist, the first Exim process
that needs it computes the data and writes it to a temporary file which is
renamed once it is complete. It does not matter if several Exim processes do
also included in the log line that records a message's arrival, keyed by
&"X="&, unless the &%tls_cipher%& log selector is turned off. The &%encrypted%&
condition can be used to test for specific cipher suites in ACLs.
-&new("(For outgoing SMTP deliveries, &$tls_cipher$& is reset &-- see section
-&<<SECID185>>&.)")
+(For outgoing SMTP deliveries, &$tls_cipher$& is reset &-- see section
+&<<SECID185>>&.)
-.new
Once TLS has been established, the ACLs that run for subsequent SMTP commands
can check the name of the cipher suite and vary their actions accordingly. The
cipher suite names vary, depending on which TLS library is being used. For
example, OpenSSL uses the name DES-CBC3-SHA for the cipher suite which in other
contexts is known as TLS_RSA_WITH_3DES_EDE_CBC_SHA. Check the OpenSSL or GnuTLS
documentation for more details.
-.wen
.section "Requesting and verifying client certificates" "SECID183"
which the client is connected. Forced failure of an expansion causes Exim to
behave as if the relevant option were unset.
-.new
.vindex &$tls_cipher$&
.vindex &$tls_peerdn$&
Before an SMTP connection is established, the &$tls_cipher$& and &$tls_peerdn$&
that were set when the message was received.) If STARTTLS is subsequently
successfully obeyed, these variables are set to the relevant values for the
outgoing connection.
-.wen
.irow &%acl_smtp_mail%& "ACL for MAIL"
.irow &%acl_smtp_mailauth%& "ACL for the AUTH parameter of MAIL"
.irow &%acl_smtp_mime%& "ACL for content-scanning MIME parts"
-.irow &new(&%acl_smtp_notquit%&) "ACL for non-QUIT terminations"
+.irow &%acl_smtp_notquit%& "ACL for non-QUIT terminations"
.irow &%acl_smtp_predata%& "ACL at start of DATA command"
.irow &%acl_smtp_quit%& "ACL for QUIT"
.irow &%acl_smtp_rcpt%& "ACL for RCPT"
-.new
.section "The not-QUIT ACL" "SECTNOTQUITACL"
-The not-QUIT ACL, specified by &%smtp_notquit_acl%&, is run in most cases when
+.vindex &$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
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.
-.wen
.section "Finding an ACL to use" "SECID195"
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.
&` 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'&>
.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.
-.new
The key that was used for a successful DNS list lookup is put into the variable
&$dnslist_matched$& (see section &<<SECID204>>&).
-.wen
.section "Variables set from DNS lists" "SECID204"
-.new
.cindex "expansion" "variables, set from DNS list"
.cindex "DNS list" "variables set from"
.vindex "&$dnslist_domain$&"
.endd
If this condition succeeds, the value in &$dnslist_matched$& might be
&`192.168.6.7`& (for example).
-.wen
If more than one address record is returned by the DNS lookup, all the IP
addresses are included in &$dnslist_value$&, separated by commas and spaces.
send in each time interval. It also specifies the number of messages permitted
in a fast burst. By increasing both &'m'& and &'p'& but keeping &'m/p'&
constant, you can allow a client to send more messages in a burst without
-changing its overall sending rate limit. Conversely, if &'m'& and &'p'& are
+changing its long-term sending rate limit. Conversely, if &'m'& and &'p'& are
both small, messages must be sent at an even rate.
There is a script in &_util/ratelimit.pl_& which extracts sending rates from
instructions when it is run with no arguments.
The key is used to look up the data for calculating the client's average
-sending rate. This data is stored in a database maintained by Exim in its spool
-directory, alongside the retry and other hints databases. The default key is
-&$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$& is only meaningful if the client has
-authenticated, and you can check with the &%authenticated%& ACL condition.
+authenticated (which you can check with the &%authenticated%& ACL condition).
-.new
-If you want to limit the rate at which a recipient receives messages, you can
-use the key &`$local_part@$domain`& with the &%per_rcpt%& option (see below) in
-a RCPT ACL.
-.wen
+The lookup key does not have to identify clients: If you want to limit the
+rate at which a recipient receives messages, you can use the key
+&`$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.
-.new
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 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.
-.wen
.section "Ratelimit options for what is being measured" "ratoptmea"
The &%per_conn%& option limits the client's connection rate.
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 incremented is equal to &%$recipients_count%&
+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.
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 &new("it is actually
-allowed. If the client is over the limit it may be subjected to
-counter-measures in the ACL 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:
+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)
+ 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
hints, the callout cache, and ratelimit data).
-.new
.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
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.
-.wen
timeout checks succeed. The &$prvscheck_result$& variable contains the result
of the checks (empty for failure, &"1"& for success).
-There are two more issues you must consider when implementing prvs-signing.
-Firstly, you need to ensure that prvs-signed addresses are not blocked by your
-ACLs. A prvs-signed address contains a slash character, but the default Exim
-configuration contains this statement in the RCPT ACL:
-.code
-deny message = Restricted characters in address
- domains = +local_domains
- local_parts = ^[.] : ^.*[@%!/|]
-.endd
-This is a conservative rule that blocks local parts that contain slashes. You
-should remove the slash in the last line.
-
-Secondly, you have to ensure that the routers accept prvs-signed addresses and
+There is one more issue you must consider when implementing prvs-signing:
+you have to ensure that the routers accept prvs-signed addresses and
deliver them correctly. The easiest way to handle this is to use a &(redirect)&
router to remove the signature with a configuration along these lines:
.code
&*Warning*&: It is not possible to use the UNIX socket connection method with
multiple &%spamd%& servers.
+The &%spamd_address%& variable is expanded before use if it starts with
+a dollar sign. In this case, the expansion may return a string that is
+used as the list so that multiple spamd servers can be the result of an
+expansion.
.section "Calling SpamAssassin from an Exim ACL" "SECID206"
Here is a simple example of the use of the &%spam%& condition in a DATA ACL:
.vitem &$spam_score_int$&
The spam score of the message, multiplied by ten, as an integer value. For
-example &"34"& or &"305"&. This is useful for numeric comparisons in
+example &"34"& or &"305"&. It may appear to disagree with &$spam_score$&
+because &$spam_score$& is rounded and &$spam_score_int$& is truncated.
+The integer value is useful for numeric comparisons in
conditions. 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
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
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 &new(&'Content-Type:'&) header line. When a call to a MIME
+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.
.section "Available Exim variables" "SECID208"
-.new
.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 expansion variable,
including &$recipients$&, by calling &'expand_string()'&. The exported
C variables are as follows:
-.wen
.vlist
.vitem &*int&~body_linecount*&
-.new
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.
-.wen
.vitem &*unsigned&~int&~debug_selector*&
This variable is set to zero when no debugging is taking place. Otherwise, it
.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 context.
+.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_signing_domains%& 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_signing_domains%& already contains a colon-
+separated list of signer domains for the message. When &%dkim_verify_signers%&
+is not specified in the main configuration, it defaults as:
+.code
+dkim_verify_signers = $dkim_signing_domains
+.endd
+This leads to the default behaviour of calling &%acl_smtp_dkim%& for each
+DKIM signature in the message. Current DKIM verifiers may want to explicitly
+call the ACL for known domains or identities. This would be achieved as follows:
+.code
+dkim_verify_signers = paypal.com:ebay.com:$dkim_signing_domains
+.endd
+This would result in &%acl_smtp_dkim%& always being called for "paypal.com"
+and "ebay.com", plus all domains that have signatures in the message. You can
+also be more creative in constructing your policy. Example:
+.code
+dkim_verify_signers = $sender_address_domain:$dkim_signing_domains
+.endd
+
+Inside the &%acl_smtp_dkim%&, the following expansion variables are
+available (from most to least important):
+
+.vlist
+.vitem &%$dkim_verify_status%&
+A string describing the general status of the signature. One of
+.ilist
+&%none%&: There is no signature in the message for the current domain or
+identity.
+.next
+&%invalid%&: The signature could not be verified due to a processing error.
+More detail is available in &%$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
+ab actual signature in the message. It does NOT neccessarily carry the
+domain that is currently being evaluated. Please use the &%dkim_signers%& ACL
+condition for that.
+.vitem &%$dkim_identity%&
+The signing identity. IMPORTANT: This variable is only populated if there is
+ab actual signature in the message. It does NOT neccessarily carry the
+identity that is currently being evaluated. Please use the &%dkim_signers%& ACL
+condition for that.
+.vitem &%$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.
+This is typically used to restrict an ACL verb to a group of domains or identities, like:
+
+.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 / users / heiko / exim.git / blobdiff