-. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.56 2009/10/16 08:46:11 tom Exp $
+. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.64 2009/10/27 14:42:57 nm4 Exp $
.
. /////////////////////////////////////////////////////////////////////////////
. This is the primary source of the Exim Manual. It is an xfpt document that is
<bookinfo>
<title>Specification of the Exim Mail Transfer Agent</title>
<titleabbrev>The Exim MTA</titleabbrev>
-<date>09 June 2009</date>
+<date>27 October 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>4.70</revnumber>
- <date>10 June 2009</date>
+ <date>27 October 2009</date>
<authorinitials>PH</authorinitials>
</revision></revhistory>
<copyright><year>2009</year><holder>University of Cambridge</holder></copyright>
A number of pieces of external code are included in the Exim distribution.
.ilist
+.new
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).
+.wen
.next
.cindex "cdb" "acknowledgment"
Support for the cdb (Constant DataBase) lookup method is provided by code
For backwards compatibility, ROOT is used if DESTDIR is not set,
but this usage is deprecated.
+.new
.cindex "installing Exim" "what is not installed"
Running &'make install'& does not copy the Exim 4 conversion script
&'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.
+.wen
For the utility programs, old versions are renamed by adding the suffix &_.O_&
to their names. The Exim binary itself, however, is handled differently. It is
.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%&.
+.new
+.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.
+.wen
.vitem &%-bp%&
.oindex "&%-bp%&"
To make the authenticators work, you can use a string expansion
expression like one of the examples in &<<CHAPplaintext>>&.
+.new
Beware that the sequence of the parameters to PLAIN and LOGIN differ; the
usercode and password are in different positions. &<<CHAPplaintext>>&
covers both.
+.wen
.ecindex IIDconfiwal
Jeffrey Friedl's &'Mastering Regular Expressions'&, which is published by
O'Reilly (see &url(http://www.oreilly.com/catalog/regex2/)).
+.new
The documentation for the syntax and semantics of the regular expressions that
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.
+.wen
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
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
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"
.code
${if bool{$acl_m_privileged_sender} ...
.endd
+.wen
.vitem &*crypteq&~{*&<&'string1'&>&*}{*&<&'string2'&>&*}*&
.cindex "expansion" "encrypted comparison"
.code
server_condition = ${if pwcheck{$auth1:$auth2}}
.endd
+.new
Again, for a PLAIN authenticator configuration, this would be:
.code
server_condition = ${if pwcheck{$auth2:$auth3}}
.endd
+.wen
.vitem &*queue_running*&
.cindex "queue runner" "detecting when delivering from"
.cindex "expansion" "queue runner test"
precise size of the file that has been written. See also
&$message_body_size$&, &$body_linecount$&, and &$body_zerocount$&.
+.new
.cindex "RCPT" "value of &$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$&
contains the size supplied on the MAIL command, or -1 if no size was given. The
value may not, of course, be truthful.
+.wen
.vitem &$mime_$&&'xxx'&
A number of variables whose names start with &$mime$& are
.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 &%tls_advertise_hosts%& "advertise TLS to these hosts"
.row &%tls_certificate%& "location of server certificate"
.row &%tls_crl%& "certificate revocation list"
This option controls the protocols when GnuTLS is used in an Exim
server. For details, see section &<<SECTreqciphgnu>>&.
+.new
+.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.
+.wen
.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
: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:
+.new
+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:
+.wen
.code
X.Employee: :fail: Gone away, no forwarding address
.endd
filter itself, and the original process that reads the result and delivers it
are all run in parallel, like a shell pipeline.
+.new
The filter can perform any transformations it likes, but of course should take
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.
+.wen
.cindex "content scanning" "per user"
A transport filter can be used to provide content-scanning on a per-user basis
This option controls the protocols when GnuTLS is used in an Exim
client. For details, see section &<<SECTreqciphgnu>>&.
+.new
+.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.
+.wen
+
.option helo_data smtp string&!! "see below"
.cindex "HELO" "argument, setting"
.cindex "EHLO" "argument, setting"
ldap://ldap.example.org/} }} }
server_set_id = uid=$auth1,ou=people,o=example.org
.endd
+.new
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
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.
-
+.wen
.section "Support for different kinds of authentication" "SECID174"
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.
+.new
+ &*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.
+.wen
+
.vindex "&$host$&"
.vindex "&$host_address$&"
All the TLS options in the &(smtp)& transport are expanded before use, with
connection is closed. In these special cases, the QUIT ACL does not run.
-
+.new
.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
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.
+.wen
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%&
For example:
.code
acl_check_connect:
- deny ratelimit = 100 / 5m / strict / noupdate
+ deny ratelimit = 100 / 5m / strict / per_cmd / noupdate
log_message = RATE: $sender_rate/$sender_rate_period \
(max $sender_rate_limit)
.endd
timeout checks succeed. The &$prvscheck_result$& variable contains the result
of the checks (empty for failure, &"1"& for success).
+.new
There is one more issue you must consider when implementing prvs-signing:
you have to ensure that the routers accept prvs-signed addresses and
deliver them correctly. The easiest way to handle this is to use a &(redirect)&
router to remove the signature with a configuration along these lines:
+.wen
.code
batv_redirect:
driver = redirect
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
+.new
.chapter "Support for DKIM (DomainKeys Identified Mail) - RFC4871" "CHID12" &&&
"DKIM Support"
.cindex "DKIM"
Calling the ACL only for existing signatures is not sufficient to build
more advanced policies. For that reason, the global option
&%dkim_verify_signers%&, and a global expansion variable
-&%$dkim_signing_domains%& exist.
+&%$dkim_signers%& exist.
The global option &%dkim_verify_signers%& can be set to a colon-separated
list of DKIM domains or identities for which the ACL &%acl_smtp_dkim%& is
called. It is expanded when the message has been received. At this point,
-the expansion variable &%$dkim_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:
+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_signing_domains
+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_signing_domains
+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 that have signatures in the message. You can
-also be more creative in constructing your policy. Example:
+and "ebay.com", plus all domains and identities 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
+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 &%$dkim_cur_signer%&
+The signer that is being evaluated in this ACL run. This can be domain or
+an identity. This is one of the list items from the expanded main option
+&%dkim_verify_signers%& (see above).
.vitem &%$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.
+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%&.
.endlist
.vitem &%$dkim_domain%&
The signing domain. IMPORTANT: This variable is only populated if there is
-ab actual signature in the message. It does NOT neccessarily carry the
-domain that is currently being evaluated. Please use the &%dkim_signers%& ACL
-condition for that.
+an actual signature in the message for the current domain or identity (as
+reflected by &%$dkim_cur_signer%&).
.vitem &%$dkim_identity%&
-The signing identity. IMPORTANT: This variable is only populated if there is
-ab actual signature in the message. It does NOT neccessarily carry the
-identity that is currently being evaluated. Please use the &%dkim_signers%& ACL
-condition for that.
+The signing identity, if present. IMPORTANT: This variable is only populated
+if there is an actual signature in the message for the current domain or
+identity (as reflected by &%$dkim_cur_signer%&).
.vitem &%$dkim_selector%&
The key record selector string
.vitem &%$dkim_algo%&
.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:
+for a match against the domain or identity that the ACL is currently verifying
+(reflected by &%$dkim_cur_signer%&). This is typically used to restrict an ACL
+verb to a group of domains or identities, like:
.code
# Warn when message apparently from GMail has no signature at all
see the documentation of the &%$dkim_verify_status%& expansion variable above
for more information of what they mean.
.endlist
-
+.wen
. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////
git://git.exim.org / users / heiko / exim.git / blobdiff