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<book>
<bookinfo>
<title>Specification of the Exim Mail Transfer Agent</title>
<titleabbrev>The Exim MTA</titleabbrev>
<date>08 January 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>
<revhistory><revision>
  <revnumber>4.66</revnumber>
  <date>08 January 2007</date>
  <authorinitials>PH</authorinitials>
</revision></revhistory>
<copyright><year>2007</year><holder>University of Cambridge</holder></copyright>
</bookinfo>
<chapter>
<title>Introduction</title>

<indexterm role="concept">
  <primary>$1, $2, etc.</primary>
  <see><emphasis>numerical variables</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>address</primary>
  <secondary>rewriting</secondary>
  <see><emphasis>rewriting</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>Bounce Address Tag Validation</primary>
  <see><emphasis>BATV</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>Client SMTP Authorization</primary>
  <see><emphasis>CSA</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>CR character</primary>
  <see><emphasis>carriage return</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>CRL</primary>
  <see><emphasis>certificate revocation list</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>delivery</primary>
  <secondary>failure report</secondary>
  <see><emphasis>bounce message</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>dialup</primary>
  <see><emphasis>intermittently connected hosts</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>exiscan</primary>
  <see><emphasis>content scanning</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>failover</primary>
  <see><emphasis>fallback</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>fallover</primary>
  <see><emphasis>fallback</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>filter</primary>
  <secondary>Sieve</secondary>
  <see><emphasis>Sieve filter</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>ident</primary>
  <see><emphasis>RFC 1413</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>LF character</primary>
  <see><emphasis>linefeed</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>maximum</primary>
  <see><emphasis>limit</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>monitor</primary>
  <see><emphasis>Exim monitor</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>no_<emphasis>xxx</emphasis></primary>
  <see>entry for xxx</see>
</indexterm>
<indexterm role="concept">
  <primary>NUL</primary>
  <see><emphasis>binary zero</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>passwd file</primary>
  <see><emphasis>/etc/passwd</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>process id</primary>
  <see><emphasis>pid</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>RBL</primary>
  <see><emphasis>DNS list</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>redirection</primary>
  <see><emphasis>address redirection</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>return path</primary>
  <seealso><emphasis>envelope sender</emphasis></seealso>
</indexterm>
<indexterm role="concept">
  <primary>scanning</primary>
  <see><emphasis>content scanning</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>SSL</primary>
  <see><emphasis>TLS</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>string</primary>
  <secondary>expansion</secondary>
  <see><emphasis>expansion</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>top bit</primary>
  <see><emphasis>8-bit characters</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>variables</primary>
  <see><emphasis>expansion, variables</emphasis></see>
</indexterm>
<indexterm role="concept">
  <primary>zero, binary</primary>
  <see><emphasis>binary zero</emphasis></see>
</indexterm>

<para>
Exim is a mail transfer agent (MTA) for hosts that are running Unix or
Unix-like operating systems. It was designed on the assumption that it would be
run on hosts that are permanently connected to the Internet. However, it can be
used on intermittently connected hosts with suitable configuration adjustments.
</para>
<section>
<title>Exim documentation</title>
<para revisionflag="changed">
<indexterm role="concept">
<primary>documentation</primary>
</indexterm>
This edition of the Exim specification applies to version 4.66 of Exim.
Substantive changes from the 4.63 edition are marked in some
renditions of the document; this paragraph is so marked if the rendition is
capable of showing a change indicator.
</para>
<para>
<indexterm role="concept">
<primary>Debian</primary>
<secondary>information sources</secondary>
</indexterm>
If you are using a Debian distribution of Exim, you will find information about
Debian-specific features in the file
</para>
<literallayout>
<filename>/usr/share/doc/exim4-base/README.Debian</filename>
</literallayout>
<para>
The command <command>man update-exim.conf</command> is another source of Debian-specific
information.
</para>
</section>
</chapter>

<chapter>
<title>Incorporated code</title>
<para>
<indexterm role="concept">
<primary>incorporated code</primary>
</indexterm>
<indexterm role="concept">
<primary>regular expressions</primary>
<secondary>library</secondary>
</indexterm>
<indexterm role="concept">
<primary>PCRE</primary>
</indexterm>
A number of pieces of external code are included in the Exim distribution.
</para>
<itemizedlist>
<listitem>
<para>
Regular expressions are supported in the main Exim program and in the Exim
monitor using the freely-distributable PCRE library, copyright &copy;
University of Cambridge. The source is distributed in the directory
<filename>src/pcre</filename>. However, this is a cut-down version of PCRE. If you want to use
the PCRE library in other programs, you should obtain and install the full
version from <emphasis role="bold"><ulink url="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre</ulink></emphasis>.
</para>
</listitem>
<listitem>
<para>
<indexterm role="concept">
<primary>cdb</primary>
<secondary>acknowledgement</secondary>
</indexterm>
Support for the cdb (Constant DataBase) lookup method is provided by code
contributed by Nigel Metheringham of (at the time he contributed it) Planet
Online Ltd. The implementation is completely contained within the code of Exim.
It does not link against an external cdb library. The code contains the
following statements:
</para>
<blockquote>
<para>
Copyright &copy; 1998 Nigel Metheringham, Planet Online Ltd
</para>
<para>
This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later
version.
</para>
<para>
This code implements Dan Bernstein&#x2019;s Constant DataBase (cdb) spec. Information,
the spec and sample code for cdb can be obtained from
<emphasis role="bold"><ulink url="http://www.pobox.com/~djb/cdb.html">http://www.pobox.com/~djb/cdb.html</ulink></emphasis>. This implementation borrows some
code from Dan Bernstein&#x2019;s implementation (which has no license restrictions
applied to it).
</para>
</blockquote>
</listitem>
<listitem>
<para>
<indexterm role="concept">
<primary>SPA authentication</primary>
</indexterm>
<indexterm role="concept">
<primary>Samba project</primary>
</indexterm>
<indexterm role="concept">
<primary>Microsoft Secure Password Authentication</primary>
</indexterm>
Client support for Microsoft&#x2019;s <emphasis>Secure Password Authentication</emphasis> is provided
by code contributed by Marc Prud&#x2019;hommeaux. Server support was contributed by
Tom Kistner. This includes code taken from the Samba project, which is released
under the Gnu GPL.
</para>
</listitem>
<listitem>
<para>
<indexterm role="concept">
<primary>Cyrus</primary>
</indexterm>
<indexterm role="concept">
<primary><emphasis>pwcheck</emphasis> daemon</primary>
</indexterm>
<indexterm role="concept">
<primary><emphasis>pwauthd</emphasis> daemon</primary>
</indexterm>
Support for calling the Cyrus <emphasis>pwcheck</emphasis> and <emphasis>saslauthd</emphasis> daemons is provided
by code taken from the Cyrus-SASL library and adapted by Alexander S.
Sabourenkov. The permission notice appears below, in accordance with the
conditions expressed therein.
</para>
<blockquote>
<para>
Copyright &copy; 2001 Carnegie Mellon University.  All rights reserved.
</para>
<para>
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
</para>
<orderedlist numeration="arabic">
<listitem>
<para>
Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
</para>
</listitem>
<listitem>
<para>
Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
</para>
</listitem>
<listitem>
<para>
The name <quote>Carnegie Mellon University</quote> must not be used to
endorse or promote products derived from this software without
prior written permission. For permission or any other legal
details, please contact
</para>
<literallayout>
              Office of Technology Transfer
              Carnegie Mellon University
              5000 Forbes Avenue
              Pittsburgh, PA  15213-3890
              (412) 268-4387, fax: (412) 268-7395
              tech-transfer@andrew.cmu.edu
</literallayout>
</listitem>
<listitem>
<para>
Redistributions of any form whatsoever must retain the following
acknowledgment:
</para>
<para>
<quote>This product includes software developed by Computing Services
at Carnegie Mellon University (<emphasis role="bold"><ulink url="http://www.cmu.edu/computing/">http://www.cmu.edu/computing/</ulink></emphasis>.</quote>
</para>
<para>
CARNEGIE MELLON UNIVERSITY DISCLAIMS ALL WARRANTIES WITH REGARD TO
THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
AND FITNESS, IN NO EVENT SHALL CARNEGIE MELLON UNIVERSITY BE LIABLE
FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
</para>
</listitem>
</orderedlist>
</blockquote>
</listitem>
<listitem>
<para>
<indexterm role="concept">
<primary>Exim monitor</primary>
<secondary>acknowledgement</secondary>
</indexterm>
<indexterm role="concept">
<primary>X-windows</primary>
</indexterm>
<indexterm role="concept">
<primary>Athena</primary>
</indexterm>
The Exim Monitor program, which is an X-Window application, includes
modified versions of the Athena StripChart and TextPop widgets.
This code is copyright by DEC and MIT, and their permission notice appears
below, in accordance with the conditions expressed therein.
</para>
<blockquote>
<para>
Copyright 1987, 1988 by Digital Equipment Corporation, Maynard, Massachusetts,
and the Massachusetts Institute of Technology, Cambridge, Massachusetts.
</para>
<para>
All Rights Reserved
</para>
<para>
Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted,
provided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in
supporting documentation, and that the names of Digital or MIT not be
used in advertising or publicity pertaining to distribution of the
software without specific, written prior permission.
</para>
<para>
DIGITAL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL
DIGITAL BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR
ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
SOFTWARE.
</para>
</blockquote>
</listitem>
<listitem>
<para>
Many people have contributed code fragments, some large, some small, that were
not covered by any specific licence requirements. It is assumed that the
contributors are happy to see their code incoporated into Exim under the GPL.
</para>
</listitem>
</itemizedlist>
</chapter>

<chapter>
<title>Building and installing Exim</title>
<para>
<indexterm role="concept" id="IIDbuex" class="startofrange">
<primary>building Exim</primary>
</indexterm>
</para>
<section>
<title>Unpacking</title>
<para>
Exim is distributed as a gzipped or bzipped tar file which, when upacked,
creates a directory with the name of the current release (for example,
<filename>exim-4.66</filename>) into which the following files are placed:
</para>
<informaltable frame="none">
<tgroup cols="2" colsep="0" rowsep="0">
<colspec colwidth="140pt" align="left"/>
<colspec colwidth="254pt" align="left"/>
<tbody>
<row>
<entry><filename>ACKNOWLEDGMENTS</filename></entry>
<entry>contains some acknowledgments</entry>
</row>
<row>
<entry><filename>CHANGES</filename></entry>
<entry>contains a reference to where changes are documented</entry>
</row>
<row>
<entry><filename>LICENCE</filename></entry>
<entry>the GNU General Public Licence</entry>
</row>
<row>
<entry><filename>Makefile</filename></entry>
<entry>top-level make file</entry>
</row>
<row>
<entry><filename>NOTICE</filename></entry>
<entry>conditions for the use of Exim</entry>
</row>
<row>
<entry><filename>README</filename></entry>
<entry>list of files, directories and simple build instructions</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
Other files whose names begin with <filename>README</filename> may also be present. The
following subdirectories are created:
</para>
<informaltable frame="none">
<tgroup cols="2" colsep="0" rowsep="0">
<colspec colwidth="140pt" align="left"/>
<colspec colwidth="254pt" align="left"/>
<tbody>
<row>
<entry><filename>Local</filename></entry>
<entry>an empty directory for local configuration files</entry>
</row>
<row>
<entry><filename>OS</filename></entry>
<entry>OS-specific files</entry>
</row>
<row>
<entry><filename>doc</filename></entry>
<entry>documentation files</entry>
</row>
<row>
<entry><filename>exim_monitor</filename></entry>
<entry>source files for the Exim monitor</entry>
</row>
<row>
<entry><filename>scripts</filename></entry>
<entry>scripts used in the build process</entry>
</row>
<row>
<entry><filename>src</filename></entry>
<entry>remaining source files</entry>
</row>
<row>
<entry><filename>util</filename></entry>
<entry>independent utilities</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The main utility programs are contained in the <filename>src</filename> directory, and are built
with the Exim binary. The <filename>util</filename> directory contains a few optional scripts
that may be useful to some sites.
</para>
</section>
</chapter>

<chapter id="CHAPmainconfig">
<title>Main configuration</title>
<para>
<indexterm role="concept" id="IIDconfima" class="startofrange">
<primary>configuration file</primary>
<secondary>main section</secondary>
</indexterm>
<indexterm role="concept" id="IIDmaiconf" class="startofrange">
<primary>main configuration</primary>
</indexterm>
The first part of the run time configuration file contains three types of item:
</para>
<itemizedlist>
<listitem>
<para>
Macro definitions: These lines start with an upper case letter.
</para>
</listitem>
<listitem>
<para>
Named list definitions: These lines start with one of the words <quote>domainlist</quote>,
<quote>hostlist</quote>, <quote>addresslist</quote>, or <quote>localpartlist</quote>.
</para>
</listitem>
<listitem>
<para>
Main configuration settings: Each setting occupies one line of the file
(with possible continuations). If any setting is preceded by the word
<quote>hide</quote>, the <option>-bP</option> command line option displays its value to admin users
only.
settings.
</para>
</listitem>
</itemizedlist>
<para>
This chapter specifies all the main configuration options, along with their
types and default values. For ease of finding a particular option, they appear
in alphabetical order in section <xref linkend="SECTalomo"/> below. However, because there
are now so many options, they are first listed briefly in functional groups, as
an aid to finding the name of the option you are looking for. Some options are
listed in more than one group.
</para>
<section>
<title>Miscellaneous</title>
<informaltable frame="none">
<tgroup cols="2" colsep="0" rowsep="0">
<colspec colwidth="196pt" align="left"/>
<colspec colwidth="254pt" align="left"/>
<tbody>
<row>
<entry><option>bi_command</option></entry>
<entry>to run for <option>-bi</option> command line option</entry>
</row>
<row>
<entry><option>disable_ipv6</option></entry>
<entry>do no IPv6 processing</entry>
</row>
<row>
<entry><option>keep_malformed</option></entry>
<entry>for broken files &ndash; should not happen</entry>
</row>
<row>
<entry><option>localhost_number</option></entry>
<entry>for unique message ids in clusters</entry>
</row>
<row>
<entry><option>message_body_visible</option></entry>
<entry>how much to show in <varname>$message_&#x200B;body</varname></entry>
</row>
<row>
<entry><option>mua_wrapper</option></entry>
<entry>run in <quote>MUA wrapper</quote> mode</entry>
</row>
<row>
<entry><option>print_topbitchars</option></entry>
<entry>top-bit characters are printing</entry>
</row>
<row>
<entry><option>timezone</option></entry>
<entry>force time zone</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</section>
<section>
<title>Exim parameters</title>
<informaltable frame="none">
<tgroup cols="2" colsep="0" rowsep="0">
<colspec colwidth="196pt" align="left"/>
<colspec colwidth="254pt" align="left"/>
<tbody>
<row>
<entry><option>exim_group</option></entry>
<entry>override compiled-in value</entry>
</row>
<row>
<entry><option>exim_path</option></entry>
<entry>override compiled-in value</entry>
</row>
<row>
<entry><option>exim_user</option></entry>
<entry>override compiled-in value</entry>
</row>
<row>
<entry><option>primary_hostname</option></entry>
<entry>default from <function>uname()</function></entry>
</row>
<row>
<entry><option>split_spool_directory</option></entry>
<entry>use multiple directories</entry>
</row>
<row>
<entry><option>spool_directory</option></entry>
<entry>override compiled-in value</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</section>
<section>
<title>Privilege controls</title>
<informaltable frame="none">
<tgroup cols="2" colsep="0" rowsep="0">
<colspec colwidth="196pt" align="left"/>
<colspec colwidth="254pt" align="left"/>
<tbody>
<row>
<entry><option>admin_groups</option></entry>
<entry>groups that are Exim admin users</entry>
</row>
<row>
<entry><option>deliver_drop_privilege</option></entry>
<entry>drop root for delivery processes</entry>
</row>
<row>
<entry><option>local_from_check</option></entry>
<entry>insert <emphasis>Sender:</emphasis> if necessary</entry>
</row>
<row>
<entry><option>local_from_prefix</option></entry>
<entry>for testing <emphasis>From:</emphasis> for local sender</entry>
</row>
<row>
<entry><option>local_from_suffix</option></entry>
<entry>for testing <emphasis>From:</emphasis> for local sender</entry>
</row>
<row>
<entry><option>local_sender_retain</option></entry>
<entry>keep <emphasis>Sender:</emphasis> from untrusted user</entry>
</row>
<row>
<entry><option>never_users</option></entry>
<entry>do not run deliveries as these</entry>
</row>
<row>
<entry><option>prod_requires_admin</option></entry>
<entry>forced delivery requires admin user</entry>
</row>
<row>
<entry><option>queue_list_requires_admin</option></entry>
<entry>queue listing requires admin user</entry>
</row>
<row>
<entry><option>trusted_groups</option></entry>
<entry>groups that are trusted</entry>
</row>
<row>
<entry><option>trusted_users</option></entry>
<entry>users that are trusted</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</section>
<section id="SECTalomo">
<title>Alphabetical list of main options</title>
<para>
Those options that undergo string expansion before use are marked with
&dagger;.
</para>
<para>
<indexterm role="option">
<primary><option>accept_&#x200B;8bitmime</option></primary>
</indexterm>
</para>
<informaltable frame="all">
<tgroup cols="4" colsep="0" rowsep="0">
<colspec colwidth="8*" align="left"/>
<colspec colwidth="5*" align="center"/>
<colspec colwidth="5*" align="center"/>
<colspec colwidth="6*" align="right"/>
<tbody>
<row>
<entry><option>accept_8bitmime</option></entry>
<entry>Use: <emphasis>main</emphasis></entry>
<entry>Type: <emphasis>boolean</emphasis></entry>
<entry>Default: <emphasis>false</emphasis></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
<indexterm role="concept">
<primary>8BITMIME</primary>
</indexterm>
<indexterm role="concept">
<primary>8-bit characters</primary>
</indexterm>
This option causes Exim to send 8BITMIME in its response to an SMTP
EHLO command, and to accept the BODY= parameter on MAIL commands.
However, though Exim is 8-bit clean, it is not a protocol converter, and it
takes no steps to do anything special with messages received by this route.
Consequently, this option is turned off by default.
</para>
<informaltable frame="all">
<tgroup cols="4" colsep="0" rowsep="0">
<colspec colwidth="8*" align="left"/>
<colspec colwidth="5*" align="center"/>
<colspec colwidth="5*" align="center"/>
<colspec colwidth="6*" align="right"/>
<tbody>
<row>
<entry><option>extract_addresses_remove_ &nbsp;arguments</option></entry>
<entry>Use: <emphasis>main</emphasis></entry>
<entry>Type: <emphasis>boolean</emphasis></entry>
<entry>Default: <emphasis>true</emphasis></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
<indexterm role="concept">
<primary><option>-t</option> option</primary>
</indexterm>
<indexterm role="concept">
<primary>command line</primary>
<secondary>addresses with <option>-t</option></secondary>
</indexterm>
<indexterm role="concept">
<primary>Sendmail compatibility</primary>
<secondary><option>-t</option> option</secondary>
</indexterm>
According to some Sendmail documentation (Sun, IRIX, HP-UX), if any addresses
are present on the command line when the <option>-t</option> option is used to build an
envelope from a message&#x2019;s <emphasis>To:</emphasis>, <emphasis>Cc:</emphasis> and <emphasis>Bcc:</emphasis> headers, the command
line addresses are removed from the recipients list. This is also how Smail
behaves. However, other Sendmail documentation (the O&#x2019;Reilly book) states that
command line addresses are added to those obtained from the header lines. When
<option>extract_&#x200B;addresses_&#x200B;remove_&#x200B;arguments</option> is true (the default), Exim subtracts
argument headers. If it is set false, Exim adds rather than removes argument
addresses.
</para>
<para>
<indexterm role="option">
<primary><option>finduser_&#x200B;retries</option></primary>
</indexterm>
</para>
</section>
</chapter>

<index role="option">
<?sdop
  foot_right_recto="&chaptertitle;"
  foot_right_verso="&chaptertitle;"
?>
<title>Option index</title>
</index>

<index role="concept">
<title>Concept index</title>
</index>

</book>
