Docs: add note on DKIM signing-limit security

[exim.git] / doc / doc-docbook / spec.xfpt

. /////////////////////////////////////////////////////////////////////////////
. This is the primary source of the Exim Manual. It is an xfpt document that is
. converted into DocBook XML for subsequent conversion into printing and online
. formats. The markup used herein is "standard" xfpt markup, with some extras.
. The markup is summarized in a file called Markup.txt.
.
. WARNING: When you use the .new macro, make sure it appears *before* any
. adjacent index items; otherwise you get an empty "paragraph" which causes
. unwanted vertical space.
. /////////////////////////////////////////////////////////////////////////////

.include stdflags
.include stdmacs

. /////////////////////////////////////////////////////////////////////////////
. This outputs the standard DocBook boilerplate.
. /////////////////////////////////////////////////////////////////////////////

.docbook

. /////////////////////////////////////////////////////////////////////////////
. These lines are processing instructions for the Simple DocBook Processor that
. Philip Hazel has developed as a less cumbersome way of making PostScript and
. PDFs than using xmlto and fop. They will be ignored by all other XML
. processors.
. /////////////////////////////////////////////////////////////////////////////

.literal xml
<?sdop
  foot_right_recto="&chaptertitle; (&chapternumber;)"
  foot_right_verso="&chaptertitle; (&chapternumber;)"
  toc_chapter_blanks="yes,yes"
  table_warn_overflow="overprint"
?>
.literal off

. /////////////////////////////////////////////////////////////////////////////
. This generate the outermost <book> element that wraps then entire document.
. /////////////////////////////////////////////////////////////////////////////

.book

. /////////////////////////////////////////////////////////////////////////////
. These definitions set some parameters and save some typing.
. Update the Copyright year (only) when changing content.
. /////////////////////////////////////////////////////////////////////////////

.set previousversion "4.91"
.include ./local_params

.set ACL "access control lists (ACLs)"
.set I   "&nbsp;&nbsp;&nbsp;&nbsp;"

.macro copyyear
2018
.endmacro

. /////////////////////////////////////////////////////////////////////////////
. Additional xfpt markup used by this document, over and above the default
. provided in the xfpt library.
. /////////////////////////////////////////////////////////////////////////////

. --- Override the &$ flag to automatically insert a $ with the variable name

.flag &$  $&   "<varname>$"  "</varname>"

. --- Short flags for daggers in option headings. They will always be inside
. --- an italic string, but we want the daggers to be roman.

.flag &!!      "</emphasis>&dagger;<emphasis>"
.flag &!?      "</emphasis>&Dagger;<emphasis>"

. --- A macro for an Exim option definition heading, generating a one-line
. --- table with four columns. For cases when the option name is given with
. --- a space, so that it can be split, a fifth argument is used for the
. --- index entry.

.macro option
.arg 5
.oindex "&%$5%&"
.endarg
.arg -5
.oindex "&%$1%&"
.endarg
.itable all 0 0 4 8* left 6* center 6* center 6* right
.row "&%$1%&" "Use: &'$2'&" "Type: &'$3'&" "Default: &'$4'&"
.endtable
.endmacro

. --- A macro for the common 2-column tables. The width of the first column
. --- is suitable for the many tables at the start of the main options chapter;
. --- the small number of other 2-column tables override it.

.macro table2 196pt 254pt
.itable none 0 0 2 $1 left $2 left
.endmacro

. --- A macro that generates .row, but puts &I; at the start of the first
. --- argument, thus indenting it. Assume a minimum of two arguments, and
. --- allow up to four arguments, which is as many as we'll ever need.

.macro irow
.arg 4
.row "&I;$1" "$2" "$3" "$4"
.endarg
.arg -4
.arg 3
.row "&I;$1" "$2" "$3"
.endarg
.arg -3
.row "&I;$1" "$2"
.endarg
.endarg
.endmacro

. --- Macros for option, variable, and concept index entries. For a "range"
. --- style of entry, use .scindex for the start and .ecindex for the end. The
. --- first argument of .scindex and the only argument of .ecindex must be the
. --- ID that ties them together.

.macro cindex
&<indexterm role="concept">&
&<primary>&$1&</primary>&
.arg 2
&<secondary>&$2&</secondary>&
.endarg
&</indexterm>&
.endmacro

.macro scindex
&<indexterm role="concept" id="$1" class="startofrange">&
&<primary>&$2&</primary>&
.arg 3
&<secondary>&$3&</secondary>&
.endarg
&</indexterm>&
.endmacro

.macro ecindex
&<indexterm role="concept" startref="$1" class="endofrange"/>&
.endmacro

.macro oindex
&<indexterm role="option">&
&<primary>&$1&</primary>&
.arg 2
&<secondary>&$2&</secondary>&
.endarg
&</indexterm>&
.endmacro

.macro vindex
&<indexterm role="variable">&
&<primary>&$1&</primary>&
.arg 2
&<secondary>&$2&</secondary>&
.endarg
&</indexterm>&
.endmacro

.macro index
.echo "** Don't use .index; use .cindex or .oindex or .vindex"
.endmacro
. ////////////////////////////////////////////////////////////////////////////


. ////////////////////////////////////////////////////////////////////////////
. The <bookinfo> element is removed from the XML before processing for Ascii
. output formats.
. ////////////////////////////////////////////////////////////////////////////

.literal xml
<bookinfo>
<title>Specification of the Exim Mail Transfer Agent</title>
<titleabbrev>The Exim MTA</titleabbrev>
<date>
.fulldate
</date>
<author><firstname>Exim</firstname><surname>Maintainers</surname></author>
<authorinitials>EM</authorinitials>
<revhistory><revision>
.versiondatexml
  <authorinitials>EM</authorinitials>
</revision></revhistory>
<copyright><year>
.copyyear
           </year><holder>University of Cambridge</holder></copyright>
</bookinfo>
.literal off


. /////////////////////////////////////////////////////////////////////////////
. This chunk of literal XML implements index entries of the form "x, see y" and
. "x, see also y". However, the DocBook DTD doesn't allow <indexterm> entries
. at the top level, so we have to put the .chapter directive first.
. /////////////////////////////////////////////////////////////////////////////

.chapter "Introduction" "CHID1"
.literal xml

<indexterm role="variable">
  <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>
  <seealso><emphasis>limit</emphasis></seealso>
</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>

.literal off


. /////////////////////////////////////////////////////////////////////////////
. This is the real start of the first chapter. See the comment above as to why
. we can't have the .chapter line here.
. chapter "Introduction"
. /////////////////////////////////////////////////////////////////////////////

Exim is a mail transfer agent (MTA) for hosts that are running Unix or
Unix-like operating systems. It was designed on the assumption that it would be
run on hosts that are permanently connected to the Internet. However, it can be
used on intermittently connected hosts with suitable configuration adjustments.

Configuration files currently exist for the following operating systems: AIX,
BSD/OS (aka BSDI), Darwin (Mac OS X), DGUX, Dragonfly, FreeBSD, GNU/Hurd,
GNU/Linux, HI-OSF (Hitachi), HI-UX, HP-UX, IRIX, MIPS RISCOS, NetBSD, OpenBSD,
OpenUNIX, QNX, SCO, SCO SVR4.2 (aka UNIX-SV), Solaris (aka SunOS5), SunOS4,
Tru64-Unix (formerly Digital UNIX, formerly DEC-OSF1), Ultrix, and Unixware.
Some of these operating systems are no longer current and cannot easily be
tested, so the configuration files may no longer work in practice.

There are also configuration files for compiling Exim in the Cygwin environment
that can be installed on systems running Windows. However, this document does
not contain any information about running Exim in the Cygwin environment.

The terms and conditions for the use and distribution of Exim are contained in
the file &_NOTICE_&. Exim is distributed under the terms of the GNU General
Public Licence, a copy of which may be found in the file &_LICENCE_&.

The use, supply or promotion of Exim for the purpose of sending bulk,
unsolicited electronic mail is incompatible with the basic aims of the program,
which revolve around the free provision of a service that enhances the quality
of personal communications. The author of Exim regards indiscriminate
mass-mailing as an antisocial, irresponsible abuse of the Internet.

Exim owes a great deal to Smail 3 and its author, Ron Karr. Without the
experience of running and working on the Smail 3 code, I could never have
contemplated starting to write a new MTA. Many of the ideas and user interfaces
were originally taken from Smail 3, though the actual code of Exim is entirely
new, and has developed far beyond the initial concept.

Many people, both in Cambridge and around the world, have contributed to the
development and the testing of Exim, and to porting it to various operating
systems. I am grateful to them all. The distribution now contains a file called
&_ACKNOWLEDGMENTS_&, in which I have started recording the names of
contributors.


.section "Exim documentation" "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.
Substantive changes from the &previousversion; edition are marked in some
renditions of the document; this paragraph is so marked if the rendition is
capable of showing a change indicator.
.wen

This document is very much a reference manual; it is not a tutorial. The reader
is expected to have some familiarity with the SMTP mail transfer protocol and
with general Unix system administration. Although there are some discussions
and examples in places, the information is mostly organized in a way that makes
it easy to look up, rather than in a natural order for sequential reading.
Furthermore, the manual aims to cover every aspect of Exim in detail, including
a number of rarely-used, special-purpose features that are unlikely to be of
very wide interest.

.cindex "books about Exim"
An &"easier"& discussion of Exim which provides more in-depth explanatory,
introductory, and tutorial material can be found in a book entitled &'The Exim
SMTP Mail Server'& (second edition, 2007), published by UIT Cambridge
(&url(http://www.uit.co.uk/exim-book/)).

This book also contains a chapter that gives a general introduction to SMTP and
Internet mail. Inevitably, however, the book is unlikely to be fully up-to-date
with the latest release of Exim. (Note that the earlier book about Exim,
published by O'Reilly, covers Exim 3, and many things have changed in Exim 4.)

.cindex "Debian" "information sources"
If you are using a Debian distribution of Exim, you will find information about
Debian-specific features in the file
&_/usr/share/doc/exim4-base/README.Debian_&.
The command &(man update-exim.conf)& is another source of Debian-specific
information.

.cindex "&_doc/NewStuff_&"
.cindex "&_doc/ChangeLog_&"
.cindex "change log"
As the program develops, there may be features in newer versions that have not
yet made it into this document, which is updated only when the most significant
digit of the fractional part of the version number changes. Specifications of
new features that are not yet in this manual are placed in the file
&_doc/NewStuff_& in the Exim distribution.

Some features may be classified as &"experimental"&. These may change
incompatibly while they are developing, or even be withdrawn. For this reason,
they are not documented in this manual. Information about experimental features
can be found in the file &_doc/experimental.txt_&.

All changes to the program (whether new features, bug fixes, or other kinds of
change) are noted briefly in the file called &_doc/ChangeLog_&.

.cindex "&_doc/spec.txt_&"
This specification itself is available as an ASCII file in &_doc/spec.txt_& so
that it can easily be searched with a text editor. Other files in the &_doc_&
directory are:

.table2 100pt
.row &_OptionLists.txt_&     "list of all options in alphabetical order"
.row &_dbm.discuss.txt_&     "discussion about DBM libraries"
.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 &_Exim3.upgrade_&       "upgrade notes from release 2 to release 3"
.row &_Exim4.upgrade_&       "upgrade notes from release 3 to release 4"
.row &_openssl.txt_&         "installing a current OpenSSL release"
.endtable

The main specification and the specification of the filtering language are also
available in other formats (HTML, PostScript, PDF, and Texinfo). Section
&<<SECTavail>>& below tells you how to get hold of these.



.section "FTP and web sites" "SECID2"
.cindex "web site"
.cindex "FTP site"
The primary site for Exim source distributions is the &%exim.org%& FTP site,
available over HTTPS, HTTP and FTP.  These services, and the &%exim.org%&
website, are hosted at the University of Cambridge.

.cindex "wiki"
.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 (&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.
The wiki site should always redirect to the correct place, which is currently
provided by GitHub, and is open to editing by anyone with a GitHub account.

.cindex Bugzilla
An Exim Bugzilla exists at &url(https://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.
Please do not ask for configuration help in the bug-tracker.


.section "Mailing lists" "SECID3"
.cindex "mailing lists" "for Exim users"
The following Exim mailing lists exist:

.table2 140pt
.row &'exim-announce@exim.org'&   "Moderated, low volume announcements list"
.row &'exim-users@exim.org'&      "General discussion list"
.row &'exim-dev@exim.org'&        "Discussion of bugs, enhancements, etc."
.row &'exim-cvs@exim.org'&        "Automated commit messages from the VCS"
.endtable

You can subscribe to these lists, change your existing subscriptions, and view
or search the archives via the mailing lists link on the Exim home page.
.cindex "Debian" "mailing list for"
If you are using a Debian distribution of Exim, you may wish to subscribe to
the Debian-specific mailing list &'pkg-exim4-users@lists.alioth.debian.org'&
via this web page:
.display
&url(http://lists.alioth.debian.org/mailman/listinfo/pkg-exim4-users)
.endd
Please ask Debian-specific questions on this list and not on the general Exim
lists.

.section "Bug reports" "SECID5"
.cindex "bug reports"
.cindex "reporting bugs"
Reports of obvious bugs can be emailed to &'bugs@exim.org'& or reported
via the Bugzilla (&url(https://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.



.section "Where to find the Exim distribution" "SECTavail"
.cindex "FTP site"
.cindex "HTTPS download site"
.cindex "distribution" "ftp site"
.cindex "distribution" "https site"
The master distribution site for the Exim distribution is
.display
&*https://downloads.exim.org/*&
.endd
The service is available over HTTPS, HTTP and FTP.
We encourage people to migrate to HTTPS.

The content served at &'https://downloads.exim.org/'& is identical to the
content served at &'https://ftp.exim.org/pub/exim'& and
&'ftp://ftp.exim.org/pub/exim'&.

If accessing via a hostname containing &'ftp'&, then the file references that
follow are relative to the &_exim_& directories at these sites.
If accessing via the hostname &'downloads'& then the subdirectories described
here are top-level directories.

There are now quite a number of independent mirror sites around
the world. Those that I know about are listed in the file called &_Mirrors_&.

Within the top exim directory there are subdirectories called &_exim3_& (for
previous Exim 3 distributions), &_exim4_& (for the latest Exim 4
distributions), and &_Testing_& for testing versions. In the &_exim4_&
subdirectory, the current release can always be found in files called
.display
&_exim-n.nn.tar.xz_&
&_exim-n.nn.tar.gz_&
&_exim-n.nn.tar.bz2_&
.endd
where &'n.nn'& is the highest such version number in the directory. The three
files contain identical data; the only difference is the type of compression.
The &_.xz_& file is usually the smallest, while the &_.gz_& file is the
most portable to old systems.

.cindex "distribution" "signing details"
.cindex "distribution" "public key"
.cindex "public key for signed distribution"
The distributions will be PGP signed by an individual key of the Release
Coordinator.  This key will have a uid containing an email address in the
&'exim.org'& domain and will have signatures from other people, including
other Exim maintainers.  We expect that the key will be in the "strong set" of
PGP keys.  There should be a trust path to that key from Nigel Metheringham's
PGP key, a version of which can be found in the release directory in the file
&_nigel-pubkey.asc_&.  All keys used will be available in public keyserver pools,
such as &'pool.sks-keyservers.net'&.

At time of last update, releases were being made by Jeremy Harris and signed
with key &'0xBCE58C8CE41F32DF'&.  Other recent keys used for signing are those
of Heiko Schlittermann, &'0x26101B62F69376CE'&,
and of Phil Pennock, &'0x4D1E900E14C1CC04'&.

The signatures for the tar bundles are in:
.display
&_exim-n.nn.tar.xz.asc_&
&_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
find out what has changed without having to download the entire distribution.

.cindex "documentation" "available formats"
The main distribution contains ASCII versions of this specification and other
documentation; other formats of the documents are available in separate files
inside the &_exim4_& directory of the FTP site:
.display
&_exim-html-n.nn.tar.gz_&
&_exim-pdf-n.nn.tar.gz_&
&_exim-postscript-n.nn.tar.gz_&
&_exim-texinfo-n.nn.tar.gz_&
.endd
These tar files contain only the &_doc_& directory, not the complete
distribution, and are also available in &_.bz2_& and &_.xz_& forms.


.section "Limitations" "SECID6"
.ilist
.cindex "limitations of Exim"
.cindex "bang paths" "not handled by Exim"
Exim is designed for use as an Internet MTA, and therefore handles addresses in
RFC 2822 domain format only. It cannot handle UUCP &"bang paths"&, though
simple two-component bang paths can be converted by a straightforward rewriting
configuration. This restriction does not prevent Exim from being interfaced to
UUCP as a transport mechanism, provided that domain addresses are used.
.next
.cindex "domainless addresses"
.cindex "address" "without domain"
Exim insists that every address it handles has a domain attached. For incoming
local messages, domainless addresses are automatically qualified with a
configured domain value. Configuration options specify from which remote
systems unqualified addresses are acceptable. These are then qualified on
arrival.
.next
.cindex "transport" "external"
.cindex "external transports"
The only external transport mechanisms that are currently implemented are SMTP
and LMTP over a TCP/IP network (including support for IPv6). However, a pipe
transport is available, and there are facilities for writing messages to files
and pipes, optionally in &'batched SMTP'& format; these facilities can be used
to send messages to other transport mechanisms such as UUCP, provided they can
handle domain-style addresses. Batched SMTP input is also catered for.
.next
Exim is not designed for storing mail for dial-in hosts. When the volumes of
such mail are large, it is better to get the messages &"delivered"& into files
(that is, off Exim's queue) and subsequently passed on to the dial-in hosts by
other means.
.next
Although Exim does have basic facilities for scanning incoming messages, these
are not comprehensive enough to do full virus or spam scanning. Such operations
are best carried out using additional specialized software packages. If you
compile Exim with the content-scanning extension, straightforward interfaces to
a number of common scanners are provided.
.endlist


.section "Run time configuration" "SECID7"
Exim's run time configuration is held in a single text file that is divided
into a number of sections. The entries in this file consist of keywords and
values, in the style of Smail 3 configuration files. A default configuration
file which is suitable for simple online installations is provided in the
distribution, and is described in chapter &<<CHAPdefconfil>>& below.


.section "Calling interface" "SECID8"
.cindex "Sendmail compatibility" "command line interface"
Like many MTAs, Exim has adopted the Sendmail command line interface so that it
can be a straight replacement for &_/usr/lib/sendmail_& or
&_/usr/sbin/sendmail_& when sending mail, but you do not need to know anything
about Sendmail in order to run Exim. For actions other than sending messages,
Sendmail-compatible options also exist, but those that produce output (for
example, &%-bp%&, which lists the messages on the queue) do so in Exim's own
format. There are also some additional options that are compatible with Smail
3, and some further options that are new to Exim. Chapter &<<CHAPcommandline>>&
documents all Exim's command line options. This information is automatically
made into the man page that forms part of the Exim distribution.

Control of messages on the queue can be done via certain privileged command
line options. There is also an optional monitor program called &'eximon'&,
which displays current information in an X window, and which contains a menu
interface to Exim's command line administration options.



.section "Terminology" "SECID9"
.cindex "terminology definitions"
.cindex "body of message" "definition of"
The &'body'& of a message is the actual data that the sender wants to transmit.
It is the last part of a message, and is separated from the &'header'& (see
below) by a blank line.

.cindex "bounce message" "definition of"
When a message cannot be delivered, it is normally returned to the sender in a
delivery failure message or a &"non-delivery report"& (NDR). The term
&'bounce'& is commonly used for this action, and the error reports are often
called &'bounce messages'&. This is a convenient shorthand for &"delivery
failure error report"&. Such messages have an empty sender address in the
message's &'envelope'& (see below) to ensure that they cannot themselves give
rise to further bounce messages.

The term &'default'& appears frequently in this manual. It is used to qualify a
value which is used in the absence of any setting in the configuration. It may
also qualify an action which is taken unless a configuration setting specifies
otherwise.

The term &'defer'& is used when the delivery of a message to a specific
destination cannot immediately take place for some reason (a remote host may be
down, or a user's local mailbox may be full). Such deliveries are &'deferred'&
until a later time.

The word &'domain'& is sometimes used to mean all but the first component of a
host's name. It is &'not'& used in that sense here, where it normally refers to
the part of an email address following the @ sign.

.cindex "envelope, definition of"
.cindex "sender" "definition of"
A message in transit has an associated &'envelope'&, as well as a header and a
body. The envelope contains a sender address (to which bounce messages should
be delivered), and any number of recipient addresses. References to the
sender or the recipients of a message usually mean the addresses in the
envelope. An MTA uses these addresses for delivery, and for returning bounce
messages, not the addresses that appear in the header lines.

.cindex "message" "header, definition of"
.cindex "header section" "definition of"
The &'header'& of a message is the first part of a message's text, consisting
of a number of lines, each of which has a name such as &'From:'&, &'To:'&,
&'Subject:'&, etc. Long header lines can be split over several text lines by
indenting the continuations. The header is separated from the body by a blank
line.

.cindex "local part" "definition of"
.cindex "domain" "definition of"
The term &'local part'&, which is taken from RFC 2822, is used to refer to that
part of an email address that precedes the @ sign. The part that follows the
@ sign is called the &'domain'& or &'mail domain'&.

.cindex "local delivery" "definition of"
.cindex "remote delivery, definition of"
The terms &'local delivery'& and &'remote delivery'& are used to distinguish
delivery to a file or a pipe on the local host from delivery by SMTP over
TCP/IP to another host. As far as Exim is concerned, all hosts other than the
host it is running on are &'remote'&.

.cindex "return path" "definition of"
&'Return path'& is another name that is used for the sender address in a
message's envelope.

.cindex "queue" "definition of"
The term &'queue'& is used to refer to the set of messages awaiting delivery,
because this term is in widespread use in the context of MTAs. However, in
Exim's case the reality is more like a pool than a queue, because there is
normally no ordering of waiting messages.

.cindex "queue runner" "definition of"
The term &'queue runner'& is used to describe a process that scans the queue
and attempts to deliver those messages whose retry times have come. This term
is used by other MTAs, and also relates to the command &%runq%&, but in Exim
the waiting messages are normally processed in an unpredictable order.

.cindex "spool directory" "definition of"
The term &'spool directory'& is used for a directory in which Exim keeps the
messages on its queue &-- that is, those that it is in the process of
delivering. This should not be confused with the directory in which local
mailboxes are stored, which is called a &"spool directory"& by some people. In
the Exim documentation, &"spool"& is always used in the first sense.






. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////

.chapter "Incorporated code" "CHID2"
.cindex "incorporated code"
.cindex "regular expressions" "library"
.cindex "PCRE"
.cindex "OpenDMARC"
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
&copy; 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"
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:

.blockquote
Copyright &copy; 1998 Nigel Metheringham, Planet Online Ltd

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later
version.
This code implements Dan Bernstein's Constant DataBase (cdb) spec. Information,
the spec and sample code for cdb can be obtained from
&url(http://www.pobox.com/~djb/cdb.html). This implementation borrows
some code from Dan Bernstein's implementation (which has no license
restrictions applied to it).
.endblockquote
.next
.cindex "SPA authentication"
.cindex "Samba project"
.cindex "Microsoft Secure Password Authentication"
Client support for Microsoft's &'Secure Password Authentication'& is provided
by code contributed by Marc Prud'hommeaux. Server support was contributed by
Tom Kistner. This includes code taken from the Samba project, which is released
under the Gnu GPL.
.next
.cindex "Cyrus"
.cindex "&'pwcheck'& daemon"
.cindex "&'pwauthd'& daemon"
Support for calling the Cyrus &'pwcheck'& and &'saslauthd'& daemons is provided
by code taken from the Cyrus-SASL library and adapted by Alexander S.
Sabourenkov. The permission notice appears below, in accordance with the
conditions expressed therein.

.blockquote
Copyright &copy; 2001 Carnegie Mellon University.  All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:

.olist
Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
.next
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.
.next
The name &"Carnegie Mellon University"& must not be used to
endorse or promote products derived from this software without
prior written permission. For permission or any other legal
details, please contact
.display
              Office of Technology Transfer
              Carnegie Mellon University
              5000 Forbes Avenue
              Pittsburgh, PA  15213-3890
              (412) 268-4387, fax: (412) 268-7395
              tech-transfer@andrew.cmu.edu
.endd
.next
Redistributions of any form whatsoever must retain the following
acknowledgment:

&"This product includes software developed by Computing Services
at Carnegie Mellon University (&url(http://www.cmu.edu/computing/)."&

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.
.endlist
.endblockquote

.next
.cindex "Exim monitor" "acknowledgment"
.cindex "X-windows"
.cindex "Athena"
The Exim Monitor program, which is an X-Window application, includes
modified versions of the Athena StripChart and TextPop widgets.
This code is copyright by DEC and MIT, and their permission notice appears
below, in accordance with the conditions expressed therein.

.blockquote
Copyright 1987, 1988 by Digital Equipment Corporation, Maynard, Massachusetts,
and the Massachusetts Institute of Technology, Cambridge, Massachusetts.

All Rights Reserved

Permission to use, copy, modify, and distribute this software and its
documentation for any purpose and without fee is hereby granted,
provided that the above copyright notice appear in all copies and that
both that copyright notice and this permission notice appear in
supporting documentation, and that the names of Digital or MIT not be
used in advertising or publicity pertaining to distribution of the
software without specific, written prior permission.

DIGITAL DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING
ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL
DIGITAL BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR
ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION,
ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
SOFTWARE.
.endblockquote

.next
.cindex "opendmarc" "acknowledgment"
The DMARC implementation uses the OpenDMARC library which is Copyrighted by
The Trusted Domain Project. Portions of Exim source which use OpenDMARC
derived code are indicated in the respective source files. The full OpenDMARC
license is provided in the LICENSE.opendmarc file contained in the distributed
source code.

.next
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 incorporated into Exim under the GPL.
.endlist





. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////

.chapter "How Exim receives and delivers mail" "CHID11" &&&
         "Receiving and delivering mail"


.section "Overall philosophy" "SECID10"
.cindex "design philosophy"
Exim is designed to work efficiently on systems that are permanently connected
to the Internet and are handling a general mix of mail. In such circumstances,
most messages can be delivered immediately. Consequently, Exim does not
maintain independent queues of messages for specific domains or hosts, though
it does try to send several messages in a single SMTP connection after a host
has been down, and it also maintains per-host retry information.


.section "Policy control" "SECID11"
.cindex "policy control" "overview"
Policy controls are now an important feature of MTAs that are connected to the
Internet. Perhaps their most important job is to stop MTAs being abused as
&"open relays"& by misguided individuals who send out vast amounts of
unsolicited junk, and want to disguise its source. Exim provides flexible
facilities for specifying policy controls on incoming mail:

.ilist
.cindex "&ACL;" "introduction"
Exim 4 (unlike previous versions of Exim) implements policy controls on
incoming mail by means of &'Access Control Lists'& (ACLs). Each list is a
series of statements that may either grant or deny access. ACLs can be used at
several places in the SMTP dialogue while receiving a message from a remote
host. However, the most common places are after each RCPT command, and at the
very end of the message. The sysadmin can specify conditions for accepting or
rejecting individual recipients or the entire message, respectively, at these
two points (see chapter &<<CHAPACL>>&). Denial of access results in an SMTP
error code.
.next
An ACL is also available for locally generated, non-SMTP messages. In this
case, the only available actions are to accept or deny the entire message.
.next
When Exim is compiled with the content-scanning extension, facilities are
provided in the ACL mechanism for passing the message to external virus and/or
spam scanning software. The result of such a scan is passed back to the ACL,
which can then use it to decide what to do with the message.
.next
When a message has been received, either from a remote host or from the local
host, but before the final acknowledgment has been sent, a locally supplied C
function called &[local_scan()]& can be run to inspect the message and decide
whether to accept it or not (see chapter &<<CHAPlocalscan>>&). If the message
is accepted, the list of recipients can be modified by the function.
.next
Using the &[local_scan()]& mechanism is another way of calling external scanner
software. The &%SA-Exim%& add-on package works this way. It does not require
Exim to be compiled with the content-scanning extension.
.next
After a message has been accepted, a further checking mechanism is available in
the form of the &'system filter'& (see chapter &<<CHAPsystemfilter>>&). This
runs at the start of every delivery process.
.endlist



.section "User filters" "SECID12"
.cindex "filter" "introduction"
.cindex "Sieve filter"
In a conventional Exim configuration, users are able to run private filters by
setting up appropriate &_.forward_& files in their home directories. See
chapter &<<CHAPredirect>>& (about the &(redirect)& router) for the
configuration needed to support this, and the separate document entitled
&'Exim's interfaces to mail filtering'& for user details. Two different kinds
of filtering are available:

.ilist
Sieve filters are written in the standard filtering language that is defined
by RFC 3028.
.next
Exim filters are written in a syntax that is unique to Exim, but which is more
powerful than Sieve, which it pre-dates.
.endlist

User filters are run as part of the routing process, described below.



.section "Message identification" "SECTmessiden"
.cindex "message ids" "details of format"
.cindex "format" "of message id"
.cindex "id of message"
.cindex "base62"
.cindex "base36"
.cindex "Darwin"
.cindex "Cygwin"
Every message handled by Exim is given a &'message id'& which is sixteen
characters long. It is divided into three parts, separated by hyphens, for
example &`16VDhn-0001bo-D3`&. Each part is a sequence of letters and digits,
normally encoding numbers in base 62. However, in the Darwin operating
system (Mac OS X) and when Exim is compiled to run under Cygwin, base 36
(avoiding the use of lower case letters) is used instead, because the message
id is used to construct file names, and the names of files in those systems are
not always case-sensitive.

.cindex "pid (process id)" "re-use of"
The detail of the contents of the message id have changed as Exim has evolved.
Earlier versions relied on the operating system not re-using a process id (pid)
within one second. On modern operating systems, this assumption can no longer
be made, so the algorithm had to be changed. To retain backward compatibility,
the format of the message id was retained, which is why the following rules are
somewhat eccentric:

.ilist
The first six characters of the message id are the time at which the message
started to be received, to a granularity of one second. That is, this field
contains the number of seconds since the start of the epoch (the normal Unix
way of representing the date and time of day).
.next
After the first hyphen, the next six characters are the id of the process that
received the message.
.next
There are two different possibilities for the final two characters:
.olist
.oindex "&%localhost_number%&"
If &%localhost_number%& is not set, this value is the fractional part of the
time of reception, normally in units of 1/2000 of a second, but for systems
that must use base 36 instead of base 62 (because of case-insensitive file
systems), the units are 1/1000 of a second.
.next
If &%localhost_number%& is set, it is multiplied by 200 (100) and added to
the fractional part of the time, which in this case is in units of 1/200
(1/100) of a second.
.endlist
.endlist

After a message has been received, Exim waits for the clock to tick at the
appropriate resolution before proceeding, so that if another message is
received by the same process, or by another process with the same (re-used)
pid, it is guaranteed that the time will be different. In most cases, the clock
will already have ticked while the message was being received.


.section "Receiving mail" "SECID13"
.cindex "receiving mail"
.cindex "message" "reception"
The only way Exim can receive mail from another host is using SMTP over
TCP/IP, in which case the sender and recipient addresses are transferred using
SMTP commands. However, from a locally running process (such as a user's MUA),
there are several possibilities:

.ilist
If the process runs Exim with the &%-bm%& option, the message is read
non-interactively (usually via a pipe), with the recipients taken from the
command line, or from the body of the message if &%-t%& is also used.
.next
If the process runs Exim with the &%-bS%& option, the message is also read
non-interactively, but in this case the recipients are listed at the start of
the message in a series of SMTP RCPT commands, terminated by a DATA
command. This is so-called &"batch SMTP"& format,
but it isn't really SMTP. The SMTP commands are just another way of passing
envelope addresses in a non-interactive submission.
.next
If the process runs Exim with the &%-bs%& option, the message is read
interactively, using the SMTP protocol. A two-way pipe is normally used for
passing data between the local process and the Exim process.
This is &"real"& SMTP and is handled in the same way as SMTP over TCP/IP. For
example, the ACLs for SMTP commands are used for this form of submission.
.next
A local process may also make a TCP/IP call to the host's loopback address
(127.0.0.1) or any other of its IP addresses. When receiving messages, Exim
does not treat the loopback address specially. It treats all such connections
in the same way as connections from other hosts.
.endlist


.cindex "message sender, constructed by Exim"
.cindex "sender" "constructed by Exim"
In the three cases that do not involve TCP/IP, the sender address is
constructed from the login name of the user that called Exim and a default
qualification domain (which can be set by the &%qualify_domain%& configuration
option). For local or batch SMTP, a sender address that is passed using the
SMTP MAIL command is ignored. However, the system administrator may allow
certain users (&"trusted users"&) to specify a different sender address
unconditionally, or all users to specify certain forms of different sender
address. The &%-f%& option or the SMTP MAIL command is used to specify these
different addresses. See section &<<SECTtrustedadmin>>& for details of trusted
users, and the &%untrusted_set_sender%& option for a way of allowing untrusted
users to change sender addresses.

Messages received by either of the non-interactive mechanisms are subject to
checking by the non-SMTP ACL, if one is defined. Messages received using SMTP
(either over TCP/IP, or interacting with a local process) can be checked by a
number of ACLs that operate at different times during the SMTP session. Either
individual recipients, or the entire message, can be rejected if local policy
requirements are not met. The &[local_scan()]& function (see chapter
&<<CHAPlocalscan>>&) is run for all incoming messages.

Exim can be configured not to start a delivery process when a message is
received; this can be unconditional, or depend on the number of incoming SMTP
connections or the system load. In these situations, new messages wait on the
queue until a queue runner process picks them up. However, in standard
configurations under normal conditions, delivery is started as soon as a
message is received.





.section "Handling an incoming message" "SECID14"
.cindex "spool directory" "files that hold a message"
.cindex "file" "how a message is held"
When Exim accepts a message, it writes two files in its spool directory. The
first contains the envelope information, the current status of the message, and
the header lines, and the second contains the body of the message. The names of
the two spool files consist of the message id, followed by &`-H`& for the
file containing the envelope and header, and &`-D`& for the data file.

.cindex "spool directory" "&_input_& sub-directory"
By default all these message files are held in a single directory called
&_input_& inside the general Exim spool directory. Some operating systems do
not perform very well if the number of files in a directory gets large; to
improve performance in such cases, the &%split_spool_directory%& option can be
used. This causes Exim to split up the input files into 62 sub-directories
whose names are single letters or digits. When this is done, the queue is
processed one sub-directory at a time instead of all at once, which can improve
overall performance even when there are not enough files in each directory to
affect file system performance.

The envelope information consists of the address of the message's sender and
the addresses of the recipients. This information is entirely separate from
any addresses contained in the header lines. The status of the message includes
a list of recipients who have already received the message. The format of the
first spool file is described in chapter &<<CHAPspool>>&.

.cindex "rewriting" "addresses"
Address rewriting that is specified in the rewrite section of the configuration
(see chapter &<<CHAPrewrite>>&) is done once and for all on incoming addresses,
both in the header lines and the envelope, at the time the message is accepted.
If during the course of delivery additional addresses are generated (for
example, via aliasing), these new addresses are rewritten as soon as they are
generated. At the time a message is actually delivered (transported) further
rewriting can take place; because this is a transport option, it can be
different for different forms of delivery. It is also possible to specify the
addition or removal of certain header lines at the time the message is
delivered (see chapters &<<CHAProutergeneric>>& and
&<<CHAPtransportgeneric>>&).



.section "Life of a message" "SECID15"
.cindex "message" "life of"
.cindex "message" "frozen"
A message remains in the spool directory until it is completely delivered to
its recipients or to an error address, or until it is deleted by an
administrator or by the user who originally created it. In cases when delivery
cannot proceed &-- for example, when a message can neither be delivered to its
recipients nor returned to its sender, the message is marked &"frozen"& on the
spool, and no more deliveries are attempted.

.cindex "frozen messages" "thawing"
.cindex "message" "thawing frozen"
An administrator can &"thaw"& such messages when the problem has been
corrected, and can also freeze individual messages by hand if necessary. In
addition, an administrator can force a delivery error, causing a bounce message
to be sent.

.oindex "&%timeout_frozen_after%&"
.oindex "&%ignore_bounce_errors_after%&"
There are options called &%ignore_bounce_errors_after%& and
&%timeout_frozen_after%&, which discard frozen messages after a certain time.
The first applies only to frozen bounces, the second to any frozen messages.

.cindex "message" "log file for"
.cindex "log" "file for each message"
While Exim is working on a message, it writes information about each delivery
attempt to its main log file. This includes successful, unsuccessful, and
delayed deliveries for each recipient (see chapter &<<CHAPlog>>&). The log
lines are also written to a separate &'message log'& file for each message.
These logs are solely for the benefit of the administrator, and are normally
deleted along with the spool files when processing of a message is complete.
The use of individual message logs can be disabled by setting
&%no_message_logs%&; this might give an improvement in performance on very busy
systems.

.cindex "journal file"
.cindex "file" "journal"
All the information Exim itself needs to set up a delivery is kept in the first
spool file, along with the header lines. When a successful delivery occurs, the
address is immediately written at the end of a journal file, whose name is the
message id followed by &`-J`&. At the end of a delivery run, if there are some
addresses left to be tried again later, the first spool file (the &`-H`& file)
is updated to indicate which these are, and the journal file is then deleted.
Updating the spool file is done by writing a new file and renaming it, to
minimize the possibility of data loss.

Should the system or the program crash after a successful delivery but before
the spool file has been updated, the journal is left lying around. The next
time Exim attempts to deliver the message, it reads the journal file and
updates the spool file before proceeding. This minimizes the chances of double
deliveries caused by crashes.



.section "Processing an address for delivery" "SECTprocaddress"
.cindex "drivers" "definition of"
.cindex "router" "definition of"
.cindex "transport" "definition of"
The main delivery processing elements of Exim are called &'routers'& and
&'transports'&, and collectively these are known as &'drivers'&. Code for a
number of them is provided in the source distribution, and compile-time options
specify which ones are included in the binary. Run time options specify which
ones are actually used for delivering messages.

.cindex "drivers" "instance definition"
Each driver that is specified in the run time configuration is an &'instance'&
of that particular driver type. Multiple instances are allowed; for example,
you can set up several different &(smtp)& transports, each with different
option values that might specify different ports or different timeouts. Each
instance has its own identifying name. In what follows we will normally use the
instance name when discussing one particular instance (that is, one specific
configuration of the driver), and the generic driver name when discussing
the driver's features in general.

A &'router'& is a driver that operates on an address, either determining how
its delivery should happen, by assigning it to a specific transport, or
converting the address into one or more new addresses (for example, via an
alias file). A router may also explicitly choose to fail an address, causing it
to be bounced.

A &'transport'& is a driver that transmits a copy of the message from Exim's
spool to some destination. There are two kinds of transport: for a &'local'&
transport, the destination is a file or a pipe on the local host, whereas for a
&'remote'& transport the destination is some other host. A message is passed
to a specific transport as a result of successful routing. If a message has
several recipients, it may be passed to a number of different transports.

.cindex "preconditions" "definition of"
An address is processed by passing it to each configured router instance in
turn, subject to certain preconditions, until a router accepts the address or
specifies that it should be bounced. We will describe this process in more
detail shortly. First, as a simple example, we consider how each recipient
address in a message is processed in a small configuration of three routers.

To make this a more concrete example, it is described in terms of some actual
routers, but remember, this is only an example. You can configure Exim's
routers in many different ways, and there may be any number of routers in a
configuration.

The first router that is specified in a configuration is often one that handles
addresses in domains that are not recognized specially by the local host. These
are typically addresses for arbitrary domains on the Internet. A precondition
is set up which looks for the special domains known to the host (for example,
its own domain name), and the router is run for addresses that do &'not'&
match. Typically, this is a router that looks up domains in the DNS in order to
find the hosts to which this address routes. If it succeeds, the address is
assigned to a suitable SMTP transport; if it does not succeed, the router is
configured to fail the address.

The second router is reached only when the domain is recognized as one that
&"belongs"& to the local host. This router does redirection &-- also known as
aliasing and forwarding. When it generates one or more new addresses from the
original, each of them is routed independently from the start. Otherwise, the
router may cause an address to fail, or it may simply decline to handle the
address, in which case the address is passed to the next router.

The final router in many configurations is one that checks to see if the
address belongs to a local mailbox. The precondition may involve a check to
see if the local part is the name of a login account, or it may look up the
local part in a file or a database. If its preconditions are not met, or if
the router declines, we have reached the end of the routers. When this happens,
the address is bounced.



.section "Processing an address for verification" "SECID16"
.cindex "router" "for verification"
.cindex "verifying address" "overview"
As well as being used to decide how to deliver to an address, Exim's routers
are also used for &'address verification'&. Verification can be requested as
one of the checks to be performed in an ACL for incoming messages, on both
sender and recipient addresses, and it can be tested using the &%-bv%& and
&%-bvs%& command line options.

When an address is being verified, the routers are run in &"verify mode"&. This
does not affect the way the routers work, but it is a state that can be
detected. By this means, a router can be skipped or made to behave differently
when verifying. A common example is a configuration in which the first router
sends all messages to a message-scanning program, unless they have been
previously scanned. Thus, the first router accepts all addresses without any
checking, making it useless for verifying. Normally, the &%no_verify%& option
would be set for such a router, causing it to be skipped in verify mode.




.section "Running an individual router" "SECTrunindrou"
.cindex "router" "running details"
.cindex "preconditions" "checking"
.cindex "router" "result of running"
As explained in the example above, a number of preconditions are checked before
running a router. If any are not met, the router is skipped, and the address is
passed to the next router. When all the preconditions on a router &'are'& met,
the router is run. What happens next depends on the outcome, which is one of
the following:

.ilist
&'accept'&: The router accepts the address, and either assigns it to a
transport, or generates one or more &"child"& addresses. Processing the
original address ceases,
.oindex "&%unseen%&"
unless the &%unseen%& option is set on the router. This option
can be used to set up multiple deliveries with different routing (for example,
for keeping archive copies of messages). When &%unseen%& is set, the address is
passed to the next router. Normally, however, an &'accept'& return marks the
end of routing.

Any child addresses generated by the router are processed independently,
starting with the first router by default. It is possible to change this by
setting the &%redirect_router%& option to specify which router to start at for
child addresses. Unlike &%pass_router%& (see below) the router specified by
&%redirect_router%& may be anywhere in the router configuration.
.next
&'pass'&: The router recognizes the address, but cannot handle it itself. It
requests that the address be passed to another router. By default the address
is passed to the next router, but this can be changed by setting the
&%pass_router%& option. However, (unlike &%redirect_router%&) the named router
must be below the current router (to avoid loops).
.next
&'decline'&: The router declines to accept the address because it does not
recognize it at all. By default, the address is passed to the next router, but
this can be prevented by setting the &%no_more%& option. When &%no_more%& is
set, all the remaining routers are skipped. In effect, &%no_more%& converts
&'decline'& into &'fail'&.
.next
&'fail'&: The router determines that the address should fail, and queues it for
the generation of a bounce message. There is no further processing of the
original address unless &%unseen%& is set on the router.
.next
&'defer'&: The router cannot handle the address at the present time. (A
database may be offline, or a DNS lookup may have timed out.) No further
processing of the address happens in this delivery attempt. It is tried again
next time the message is considered for delivery.
.next
&'error'&: There is some error in the router (for example, a syntax error in
its configuration). The action is as for defer.
.endlist

If an address reaches the end of the routers without having been accepted by
any of them, it is bounced as unrouteable. The default error message in this
situation is &"unrouteable address"&, but you can set your own message by
making use of the &%cannot_route_message%& option. This can be set for any
router; the value from the last router that &"saw"& the address is used.

Sometimes while routing you want to fail a delivery when some conditions are
met but others are not, instead of passing the address on for further routing.
You can do this by having a second router that explicitly fails the delivery
when the relevant conditions are met. The &(redirect)& router has a &"fail"&
facility for this purpose.


.section "Duplicate addresses" "SECID17"
.cindex "case of local parts"
.cindex "address duplicate, discarding"
.cindex "duplicate addresses"
Once routing is complete, Exim scans the addresses that are assigned to local
and remote transports, and discards any duplicates that it finds. During this
check, local parts are treated as case-sensitive. This happens only when
actually delivering a message; when testing routers with &%-bt%&, all the
routed addresses are shown.



.section "Router preconditions" "SECTrouprecon"
.cindex "router" "preconditions, order of processing"
.cindex "preconditions" "order of processing"
The preconditions that are tested for each router are listed below, in the
order in which they are tested. The individual configuration options are
described in more detail in chapter &<<CHAProutergeneric>>&.

.ilist
The &%local_part_prefix%& and &%local_part_suffix%& options can specify that
the local parts handled by the router may or must have certain prefixes and/or
suffixes. If a mandatory affix (prefix or suffix) is not present, the router is
skipped. These conditions are tested first. When an affix is present, it is
removed from the local part before further processing, including the evaluation
of any other conditions.
.next
Routers can be designated for use only when not verifying an address, that is,
only when routing it for delivery (or testing its delivery routing). If the
&%verify%& option is set false, the router is skipped when Exim is verifying an
address.
Setting the &%verify%& option actually sets two options, &%verify_sender%& and
&%verify_recipient%&, which independently control the use of the router for
sender and recipient verification. You can set these options directly if
you want a router to be used for only one type of verification.
Note that cutthrough delivery is classed as a recipient verification for this purpose.
.next
If the &%address_test%& option is set false, the router is skipped when Exim is
run with the &%-bt%& option to test an address routing. This can be helpful
when the first router sends all new messages to a scanner of some sort; it
makes it possible to use &%-bt%& to test subsequent delivery routing without
having to simulate the effect of the scanner.
.next
Routers can be designated for use only when verifying an address, as
opposed to routing it for delivery. The &%verify_only%& option controls this.
Again, cutthrough delivery counts as a verification.
.next
Individual routers can be explicitly skipped when running the routers to
check an address given in the SMTP EXPN command (see the &%expn%& option).
.next
If the &%domains%& option is set, the domain of the address must be in the set
of domains that it defines.
.next
.vindex "&$local_part_prefix$&"
.vindex "&$local_part$&"
.vindex "&$local_part_suffix$&"
If the &%local_parts%& option is set, the local part of the address must be in
the set of local parts that it defines. If &%local_part_prefix%& or
&%local_part_suffix%& is in use, the prefix or suffix is removed from the local
part before this check. If you want to do precondition tests on local parts
that include affixes, you can do so by using a &%condition%& option (see below)
that uses the variables &$local_part$&, &$local_part_prefix$&, and
&$local_part_suffix$& as necessary.
.next
.vindex "&$local_user_uid$&"
.vindex "&$local_user_gid$&"
.vindex "&$home$&"
If the &%check_local_user%& option is set, the local part must be the name of
an account on the local host. If this check succeeds, the uid and gid of the
local user are placed in &$local_user_uid$& and &$local_user_gid$& and the
user's home directory is placed in &$home$&; these values can be used in the
remaining preconditions.
.next
If the &%router_home_directory%& option is set, it is expanded at this point,
because it overrides the value of &$home$&. If this expansion were left till
later, the value of &$home$& as set by &%check_local_user%& would be used in
subsequent tests. Having two different values of &$home$& in the same router
could lead to confusion.
.next
If the &%senders%& option is set, the envelope sender address must be in the
set of addresses that it defines.
.next
If the &%require_files%& option is set, the existence or non-existence of
specified files is tested.
.next
.cindex "customizing" "precondition"
If the &%condition%& option is set, it is evaluated and tested. This option
uses an expanded string to allow you to set up your own custom preconditions.
Expanded strings are described in chapter &<<CHAPexpand>>&.
.endlist


Note that &%require_files%& comes near the end of the list, so you cannot use
it to check for the existence of a file in which to lookup up a domain, local
part, or sender. However, as these options are all expanded, you can use the
&%exists%& expansion condition to make such tests within each condition. The
&%require_files%& option is intended for checking files that the router may be
going to use internally, or which are needed by a specific transport (for
example, &_.procmailrc_&).



.section "Delivery in detail" "SECID18"
.cindex "delivery" "in detail"
When a message is to be delivered, the sequence of events is as follows:

.ilist
If a system-wide filter file is specified, the message is passed to it. The
filter may add recipients to the message, replace the recipients, discard the
message, cause a new message to be generated, or cause the message delivery to
fail. The format of the system filter file is the same as for Exim user filter
files, described in the separate document entitled &'Exim's interfaces to mail
filtering'&.
.cindex "Sieve filter" "not available for system filter"
(&*Note*&: Sieve cannot be used for system filter files.)

Some additional features are available in system filters &-- see chapter
&<<CHAPsystemfilter>>& for details. Note that a message is passed to the system
filter only once per delivery attempt, however many recipients it has. However,
if there are several delivery attempts because one or more addresses could not
be immediately delivered, the system filter is run each time. The filter
condition &%first_delivery%& can be used to detect the first run of the system
filter.
.next
Each recipient address is offered to each configured router in turn, subject to
its preconditions, until one is able to handle it. If no router can handle the
address, that is, if they all decline, the address is failed. Because routers
can be targeted at particular domains, several locally handled domains can be
processed entirely independently of each other.
.next
.cindex "routing" "loops in"
.cindex "loop" "while routing"
A router that accepts an address may assign it to a local or a remote
transport. However, the transport is not run at this time. Instead, the address
is placed on a list for the particular transport, which will be run later.
Alternatively, the router may generate one or more new addresses (typically
from alias, forward, or filter files). New addresses are fed back into this
process from the top, but in order to avoid loops, a router ignores any address
which has an identically-named ancestor that was processed by itself.
.next
When all the routing has been done, addresses that have been successfully
handled are passed to their assigned transports. When local transports are
doing real local deliveries, they handle only one address at a time, but if a
local transport is being used as a pseudo-remote transport (for example, to
collect batched SMTP messages for transmission by some other means) multiple
addresses can be handled. Remote transports can always handle more than one
address at a time, but can be configured not to do so, or to restrict multiple
addresses to the same domain.
.next
Each local delivery to a file or a pipe runs in a separate process under a
non-privileged uid, and these deliveries are run one at a time. Remote
deliveries also run in separate processes, normally under a uid that is private
to Exim (&"the Exim user"&), but in this case, several remote deliveries can be
run in parallel. The maximum number of simultaneous remote deliveries for any
one message is set by the &%remote_max_parallel%& option.
The order in which deliveries are done is not defined, except that all local
deliveries happen before any remote deliveries.
.next
.cindex "queue runner"
When it encounters a local delivery during a queue run, Exim checks its retry
database to see if there has been a previous temporary delivery failure for the
address before running the local transport. If there was a previous failure,
Exim does not attempt a new delivery until the retry time for the address is
reached. However, this happens only for delivery attempts that are part of a
queue run. Local deliveries are always attempted when delivery immediately
follows message reception, even if retry times are set for them. This makes for
better behaviour if one particular message is causing problems (for example,
causing quota overflow, or provoking an error in a filter file).
.next
.cindex "delivery" "retry in remote transports"
Remote transports do their own retry handling, since an address may be
deliverable to one of a number of hosts, each of which may have a different
retry time. If there have been previous temporary failures and no host has
reached its retry time, no delivery is attempted, whether in a queue run or
not. See chapter &<<CHAPretry>>& for details of retry strategies.
.next
If there were any permanent errors, a bounce message is returned to an
appropriate address (the sender in the common case), with details of the error
for each failing address. Exim can be configured to send copies of bounce
messages to other addresses.
.next
.cindex "delivery" "deferral"
If one or more addresses suffered a temporary failure, the message is left on
the queue, to be tried again later. Delivery of these addresses is said to be
&'deferred'&.
.next
When all the recipient addresses have either been delivered or bounced,
handling of the message is complete. The spool files and message log are
deleted, though the message log can optionally be preserved if required.
.endlist




.section "Retry mechanism" "SECID19"
.cindex "delivery" "retry mechanism"
.cindex "retry" "description of mechanism"
.cindex "queue runner"
Exim's mechanism for retrying messages that fail to get delivered at the first
attempt is the queue runner process. You must either run an Exim daemon that
uses the &%-q%& option with a time interval to start queue runners at regular
intervals, or use some other means (such as &'cron'&) to start them. If you do
not arrange for queue runners to be run, messages that fail temporarily at the
first attempt will remain on your queue for ever. A queue runner process works
its way through the queue, one message at a time, trying each delivery that has
passed its retry time.
You can run several queue runners at once.

Exim uses a set of configured rules to determine when next to retry the failing
address (see chapter &<<CHAPretry>>&). These rules also specify when Exim
should give up trying to deliver to the address, at which point it generates a
bounce message. If no retry rules are set for a particular host, address, and
error combination, no retries are attempted, and temporary errors are treated
as permanent.



.section "Temporary delivery failure" "SECID20"
.cindex "delivery" "temporary failure"
There are many reasons why a message may not be immediately deliverable to a
particular address. Failure to connect to a remote machine (because it, or the
connection to it, is down) is one of the most common. Temporary failures may be
detected during routing as well as during the transport stage of delivery.
Local deliveries may be delayed if NFS files are unavailable, or if a mailbox
is on a file system where the user is over quota. Exim can be configured to
impose its own quotas on local mailboxes; where system quotas are set they will
also apply.

If a host is unreachable for a period of time, a number of messages may be
waiting for it by the time it recovers, and sending them in a single SMTP
connection is clearly beneficial. Whenever a delivery to a remote host is
deferred,
.cindex "hints database" "deferred deliveries"
Exim makes a note in its hints database, and whenever a successful
SMTP delivery has happened, it looks to see if any other messages are waiting
for the same host. If any are found, they are sent over the same SMTP
connection, subject to a configuration limit as to the maximum number in any
one connection.



.section "Permanent delivery failure" "SECID21"
.cindex "delivery" "permanent failure"
.cindex "bounce message" "when generated"
When a message cannot be delivered to some or all of its intended recipients, a
bounce message is generated. Temporary delivery failures turn into permanent
errors when their timeout expires. All the addresses that fail in a given
delivery attempt are listed in a single message. If the original message has
many recipients, it is possible for some addresses to fail in one delivery
attempt and others to fail subsequently, giving rise to more than one bounce
message. The wording of bounce messages can be customized by the administrator.
See chapter &<<CHAPemsgcust>>& for details.

.cindex "&'X-Failed-Recipients:'& header line"
Bounce messages contain an &'X-Failed-Recipients:'& header line that lists the
failed addresses, for the benefit of programs that try to analyse such messages
automatically.

.cindex "bounce message" "recipient of"
A bounce message is normally sent to the sender of the original message, as
obtained from the message's envelope. For incoming SMTP messages, this is the
address given in the MAIL command. However, when an address is expanded via a
forward or alias file, an alternative address can be specified for delivery
failures of the generated addresses. For a mailing list expansion (see section
&<<SECTmailinglists>>&) it is common to direct bounce messages to the manager
of the list.



.section "Failures to deliver bounce messages" "SECID22"
.cindex "bounce message" "failure to deliver"
If a bounce message (either locally generated or received from a remote host)
itself suffers a permanent delivery failure, the message is left on the queue,
but it is frozen, awaiting the attention of an administrator. There are options
that can be used to make Exim discard such failed messages, or to keep them
for only a short time (see &%timeout_frozen_after%& and
&%ignore_bounce_errors_after%&).





. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////

.chapter "Building and installing Exim" "CHID3"
.scindex IIDbuex "building Exim"

.section "Unpacking" "SECID23"
Exim is distributed as a gzipped or bzipped tar file which, when unpacked,
creates a directory with the name of the current release (for example,
&_exim-&version()_&) into which the following files are placed:

.table2 140pt
.irow &_ACKNOWLEDGMENTS_& "contains some acknowledgments"
.irow &_CHANGES_&         "contains a reference to where changes are &&&
  documented"
.irow &_LICENCE_&         "the GNU General Public Licence"
.irow &_Makefile_&        "top-level make file"
.irow &_NOTICE_&          "conditions for the use of Exim"
.irow &_README_&          "list of files, directories and simple build &&&
  instructions"
.endtable

Other files whose names begin with &_README_& may also be present. The
following subdirectories are created:

.table2 140pt
.irow &_Local_&           "an empty directory for local configuration files"
.irow &_OS_&              "OS-specific files"
.irow &_doc_&             "documentation files"
.irow &_exim_monitor_&    "source files for the Exim monitor"
.irow &_scripts_&         "scripts used in the build process"
.irow &_src_&             "remaining source files"
.irow &_util_&            "independent utilities"
.endtable

The main utility programs are contained in the &_src_& directory, and are built
with the Exim binary. The &_util_& directory contains a few optional scripts
that may be useful to some sites.


.section "Multiple machine architectures and operating systems" "SECID24"
.cindex "building Exim" "multiple OS/architectures"
The building process for Exim is arranged to make it easy to build binaries for
a number of different architectures and operating systems from the same set of
source files. Compilation does not take place in the &_src_& directory.
Instead, a &'build directory'& is created for each architecture and operating
system.
.cindex "symbolic link" "to build directory"
Symbolic links to the sources are installed in this directory, which is where
the actual building takes place. In most cases, Exim can discover the machine
architecture and operating system for itself, but the defaults can be
overridden if necessary.
.cindex compiler requirements
.cindex compiler version
A C99-capable compiler will be required for the build.


.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 either set the PCRE_LIBS
and INCLUDE directives appropriately,
or set PCRE_CONFIG=yes to use the installed &(pcre-config)& command.
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/).
More information on PCRE is available at &url(http://www.pcre.org/).

.section "DBM libraries" "SECTdb"
.cindex "DBM libraries" "discussion of"
.cindex "hints database" "DBM files used for"
Even if you do not use any DBM files in your configuration, Exim still needs a
DBM library in order to operate, because it uses indexed files for its hints
databases. Unfortunately, there are a number of DBM libraries in existence, and
different operating systems often have different ones installed.

.cindex "Solaris" "DBM library for"
.cindex "IRIX, DBM library for"
.cindex "BSD, DBM library for"
.cindex "Linux, DBM library for"
If you are using Solaris, IRIX, one of the modern BSD systems, or a modern
Linux distribution, the DBM configuration should happen automatically, and you
may be able to ignore this section. Otherwise, you may have to learn more than
you would like about DBM libraries from what follows.

.cindex "&'ndbm'& DBM library"
Licensed versions of Unix normally contain a library of DBM functions operating
via the &'ndbm'& interface, and this is what Exim expects by default. Free
versions of Unix seem to vary in what they contain as standard. In particular,
some early versions of Linux have no default DBM library, and different
distributors have chosen to bundle different libraries with their packaged
versions. However, the more recent releases seem to have standardized on the
Berkeley DB library.

Different DBM libraries have different conventions for naming the files they
use. When a program opens a file called &_dbmfile_&, there are several
possibilities:

.olist
A traditional &'ndbm'& implementation, such as that supplied as part of
Solaris, operates on two files called &_dbmfile.dir_& and &_dbmfile.pag_&.
.next
.cindex "&'gdbm'& DBM library"
The GNU library, &'gdbm'&, operates on a single file. If used via its &'ndbm'&
compatibility interface it makes two different hard links to it with names
&_dbmfile.dir_& and &_dbmfile.pag_&, but if used via its native interface, the
file name is used unmodified.
.next
.cindex "Berkeley DB library"
The Berkeley DB package, if called via its &'ndbm'& compatibility interface,
operates on a single file called &_dbmfile.db_&, but otherwise looks to the
programmer exactly the same as the traditional &'ndbm'& implementation.
.next
If the Berkeley package is used in its native mode, it operates on a single
file called &_dbmfile_&; the programmer's interface is somewhat different to
the traditional &'ndbm'& interface.
.next
To complicate things further, there are several very different versions of the
Berkeley DB package. Version 1.85 was stable for a very long time, releases
2.&'x'& and 3.&'x'& were current for a while, but the latest versions are now
numbered 4.&'x'&. Maintenance of some of the earlier releases has ceased. All
versions of Berkeley DB can be obtained from
&url(http://www.sleepycat.com/).
.next
.cindex "&'tdb'& DBM library"
Yet another DBM library, called &'tdb'&, is available from
&url(http://download.sourceforge.net/tdb). It has its own interface, and also
operates on a single file.
.endlist

.cindex "USE_DB"
.cindex "DBM libraries" "configuration for building"
Exim and its utilities can be compiled to use any of these interfaces. In order
to use any version of the Berkeley DB package in native mode, you must set
USE_DB in an appropriate configuration file (typically
&_Local/Makefile_&). For example:
.code
USE_DB=yes
.endd
Similarly, for gdbm you set USE_GDBM, and for tdb you set USE_TDB. An
error is diagnosed if you set more than one of these.

At the lowest level, the build-time configuration sets none of these options,
thereby assuming an interface of type (1). However, some operating system
configuration files (for example, those for the BSD operating systems and
Linux) assume type (4) by setting USE_DB as their default, and the
configuration files for Cygwin set USE_GDBM. Anything you set in
&_Local/Makefile_&, however, overrides these system defaults.

As well as setting USE_DB, USE_GDBM, or USE_TDB, it may also be
necessary to set DBMLIB, to cause inclusion of the appropriate library, as
in one of these lines:
.code
DBMLIB = -ldb
DBMLIB = -ltdb
.endd
Settings like that will work if the DBM library is installed in the standard
place. Sometimes it is not, and the library's header file may also not be in
the default path. You may need to set INCLUDE to specify where the header
file is, and to specify the path to the library more fully in DBMLIB, as in
this example:
.code
INCLUDE=-I/usr/local/include/db-4.1
DBMLIB=/usr/local/lib/db-4.1/libdb.a
.endd
There is further detailed discussion about the various DBM libraries in the
file &_doc/dbm.discuss.txt_& in the Exim distribution.



.section "Pre-building configuration" "SECID25"
.cindex "building Exim" "pre-building configuration"
.cindex "configuration for building Exim"
.cindex "&_Local/Makefile_&"
.cindex "&_src/EDITME_&"
Before building Exim, a local configuration file that specifies options
independent of any operating system has to be created with the name
&_Local/Makefile_&. A template for this file is supplied as the file
&_src/EDITME_&, and it contains full descriptions of all the option settings
therein. These descriptions are therefore not repeated here. If you are
building Exim for the first time, the simplest thing to do is to copy
&_src/EDITME_& to &_Local/Makefile_&, then read it and edit it appropriately.

There are three settings that you must supply, because Exim will not build
without them. They are the location of the run time configuration file
(CONFIGURE_FILE), the directory in which Exim binaries will be installed
(BIN_DIRECTORY), and the identity of the Exim user (EXIM_USER and
maybe EXIM_GROUP as well). The value of CONFIGURE_FILE can in fact be
a colon-separated list of file names; Exim uses the first of them that exists.

There are a few other parameters that can be specified either at build time or
at run time, to enable the same binary to be used on a number of different
machines. However, if the locations of Exim's spool directory and log file
directory (if not within the spool directory) are fixed, it is recommended that
you specify them in &_Local/Makefile_& instead of at run time, so that errors
detected early in Exim's execution (such as a malformed configuration file) can
be logged.

.cindex "content scanning" "specifying at build time"
Exim's interfaces for calling virus and spam scanning software directly from
access control lists are not compiled by default. If you want to include these
facilities, you need to set
.code
WITH_CONTENT_SCAN=yes
.endd
in your &_Local/Makefile_&. For details of the facilities themselves, see
chapter &<<CHAPexiscan>>&.


.cindex "&_Local/eximon.conf_&"
.cindex "&_exim_monitor/EDITME_&"
If you are going to build the Exim monitor, a similar configuration process is
required. The file &_exim_monitor/EDITME_& must be edited appropriately for
your installation and saved under the name &_Local/eximon.conf_&. If you are
happy with the default settings described in &_exim_monitor/EDITME_&,
&_Local/eximon.conf_& can be empty, but it must exist.

This is all the configuration that is needed in straightforward cases for known
operating systems. However, the building process is set up so that it is easy
to override options that are set by default or by operating-system-specific
configuration files, for example to change the name of the C compiler, which
defaults to &%gcc%&. See section &<<SECToverride>>& below for details of how to
do this.



.section "Support for iconv()" "SECID26"
.cindex "&[iconv()]& support"
.cindex "RFC 2047"
The contents of header lines in messages may be encoded according to the rules
described RFC 2047. This makes it possible to transmit characters that are not
in the ASCII character set, and to label them as being in a particular
character set. When Exim is inspecting header lines by means of the &%$h_%&
mechanism, it decodes them, and translates them into a specified character set
(default is set at build time). The translation is possible only if the operating system
supports the &[iconv()]& function.

However, some of the operating systems that supply &[iconv()]& do not support
very many conversions. The GNU &%libiconv%& library (available from
&url(http://www.gnu.org/software/libiconv/)) can be installed on such
systems to remedy this deficiency, as well as on systems that do not supply
&[iconv()]& at all. After installing &%libiconv%&, you should add
.code
HAVE_ICONV=yes
.endd
to your &_Local/Makefile_& and rebuild Exim.



.section "Including TLS/SSL encryption support" "SECTinctlsssl"
.cindex "TLS" "including support for TLS"
.cindex "encryption" "including support for"
.cindex "SUPPORT_TLS"
.cindex "OpenSSL" "building Exim with"
.cindex "GnuTLS" "building Exim with"
Exim can be built to support encrypted SMTP connections, using the STARTTLS
command as per RFC 2487. It can also support legacy clients that expect to
start a TLS session immediately on connection to a non-standard port (see the
&%tls_on_connect_ports%& runtime option and the &%-tls-on-connect%& command
line option).

If you want to build Exim with TLS support, you must first install either the
OpenSSL or GnuTLS library. There is no cryptographic code in Exim itself for
implementing SSL.

If OpenSSL is installed, you should set
.code
SUPPORT_TLS=yes
TLS_LIBS=-lssl -lcrypto
.endd
in &_Local/Makefile_&. You may also need to specify the locations of the
OpenSSL library and include files. For example:
.code
SUPPORT_TLS=yes
TLS_LIBS=-L/usr/local/openssl/lib -lssl -lcrypto
TLS_INCLUDE=-I/usr/local/openssl/include/
.endd
.cindex "pkg-config" "OpenSSL"
If you have &'pkg-config'& available, then instead you can just use:
.code
SUPPORT_TLS=yes
USE_OPENSSL_PC=openssl
.endd
.cindex "USE_GNUTLS"
If GnuTLS is installed, you should set
.code
SUPPORT_TLS=yes
USE_GNUTLS=yes
TLS_LIBS=-lgnutls -ltasn1 -lgcrypt
.endd
in &_Local/Makefile_&, and again you may need to specify the locations of the
library and include files. For example:
.code
SUPPORT_TLS=yes
USE_GNUTLS=yes
TLS_LIBS=-L/usr/gnu/lib -lgnutls -ltasn1 -lgcrypt
TLS_INCLUDE=-I/usr/gnu/include
.endd
.cindex "pkg-config" "GnuTLS"
If you have &'pkg-config'& available, then instead you can just use:
.code
SUPPORT_TLS=yes
USE_GNUTLS=yes
USE_GNUTLS_PC=gnutls
.endd

You do not need to set TLS_INCLUDE if the relevant directory is already
specified in INCLUDE. Details of how to configure Exim to make use of TLS are
given in chapter &<<CHAPTLS>>&.




.section "Use of tcpwrappers" "SECID27"

.cindex "tcpwrappers, building Exim to support"
.cindex "USE_TCP_WRAPPERS"
.cindex "TCP_WRAPPERS_DAEMON_NAME"
.cindex "tcp_wrappers_daemon_name"
Exim can be linked with the &'tcpwrappers'& library in order to check incoming
SMTP calls using the &'tcpwrappers'& control files. This may be a convenient
alternative to Exim's own checking facilities for installations that are
already making use of &'tcpwrappers'& for other purposes. To do this, you
should set USE_TCP_WRAPPERS in &_Local/Makefile_&, arrange for the file
&_tcpd.h_& to be available at compile time, and also ensure that the library
&_libwrap.a_& is available at link time, typically by including &%-lwrap%& in
EXTRALIBS_EXIM. For example, if &'tcpwrappers'& is installed in &_/usr/local_&,
you might have
.code
USE_TCP_WRAPPERS=yes
CFLAGS=-O -I/usr/local/include
EXTRALIBS_EXIM=-L/usr/local/lib -lwrap
.endd
in &_Local/Makefile_&. The daemon name to use in the &'tcpwrappers'& control
files is &"exim"&. For example, the line
.code
exim : LOCAL  192.168.1.  .friendly.domain.example
.endd
in your &_/etc/hosts.allow_& file allows connections from the local host, from
the subnet 192.168.1.0/24, and from all hosts in &'friendly.domain.example'&.
All other connections are denied. The daemon name used by &'tcpwrappers'&
can be changed at build time by setting TCP_WRAPPERS_DAEMON_NAME in
&_Local/Makefile_&, or by setting tcp_wrappers_daemon_name in the
configure file. Consult the &'tcpwrappers'& documentation for
further details.


.section "Including support for IPv6" "SECID28"
.cindex "IPv6" "including support for"
Exim contains code for use on systems that have IPv6 support. Setting
&`HAVE_IPV6=YES`& in &_Local/Makefile_& causes the IPv6 code to be included;
it may also be necessary to set IPV6_INCLUDE and IPV6_LIBS on systems
where the IPv6 support is not fully integrated into the normal include and
library files.

Two different types of DNS record for handling IPv6 addresses have been
defined. AAAA records (analogous to A records for IPv4) are in use, and are
currently seen as the mainstream. Another record type called A6 was proposed
as better than AAAA because it had more flexibility. However, it was felt to be
over-complex, and its status was reduced to &"experimental"&.
Exim used to
have a compile option for including A6 record support but this has now been
withdrawn.



.section "Dynamically loaded lookup module support" "SECTdynamicmodules"
.cindex "lookup modules"
.cindex "dynamic modules"
.cindex ".so building"
On some platforms, Exim supports not compiling all lookup types directly into
the main binary, instead putting some into external modules which can be loaded
on demand.
This permits packagers to build Exim with support for lookups with extensive
library dependencies without requiring all users to install all of those
dependencies.
Most, but not all, lookup types can be built this way.

Set &`LOOKUP_MODULE_DIR`& to the directory into which the modules will be
installed; Exim will only load modules from that directory, as a security
measure.  You will need to set &`CFLAGS_DYNAMIC`& if not already defined
for your OS; see &_OS/Makefile-Linux_& for an example.
Some other requirements for adjusting &`EXTRALIBS`& may also be necessary,
see &_src/EDITME_& for details.

Then, for each module to be loaded dynamically, define the relevant
&`LOOKUP_`&<&'lookup_type'&> flags to have the value "2" instead of "yes".
For example, this will build in lsearch but load sqlite and mysql support
on demand:
.code
LOOKUP_LSEARCH=yes
LOOKUP_SQLITE=2
LOOKUP_MYSQL=2
.endd


.section "The building process" "SECID29"
.cindex "build directory"
Once &_Local/Makefile_& (and &_Local/eximon.conf_&, if required) have been
created, run &'make'& at the top level. It determines the architecture and
operating system types, and creates a build directory if one does not exist.
For example, on a Sun system running Solaris 8, the directory
&_build-SunOS5-5.8-sparc_& is created.
.cindex "symbolic link" "to source files"
Symbolic links to relevant source files are installed in the build directory.

If this is the first time &'make'& has been run, it calls a script that builds
a make file inside the build directory, using the configuration files from the
&_Local_& directory. The new make file is then passed to another instance of
&'make'&. This does the real work, building a number of utility scripts, and
then compiling and linking the binaries for the Exim monitor (if configured), a
number of utility programs, and finally Exim itself. The command &`make
makefile`& can be used to force a rebuild of the make file in the build
directory, should this ever be necessary.

If you have problems building Exim, check for any comments there may be in the
&_README_& file concerning your operating system, and also take a look at the
FAQ, where some common problems are covered.



.section 'Output from &"make"&' "SECID283"
The output produced by the &'make'& process for compile lines is often very
unreadable, because these lines can be very long. For this reason, the normal
output is suppressed by default, and instead output similar to that which
appears when compiling the 2.6 Linux kernel is generated: just a short line for
each module that is being compiled or linked. However, it is still possible to
get the full output, by calling &'make'& like this:
.code
FULLECHO='' make -e
.endd
The value of FULLECHO defaults to &"@"&, the flag character that suppresses
command reflection in &'make'&. When you ask for the full output, it is
given in addition to the short output.



.section "Overriding build-time options for Exim" "SECToverride"
.cindex "build-time options, overriding"
The main make file that is created at the beginning of the building process
consists of the concatenation of a number of files which set configuration
values, followed by a fixed set of &'make'& instructions. If a value is set
more than once, the last setting overrides any previous ones. This provides a
convenient way of overriding defaults. The files that are concatenated are, in
order:
.display
&_OS/Makefile-Default_&
&_OS/Makefile-_&<&'ostype'&>
&_Local/Makefile_&
&_Local/Makefile-_&<&'ostype'&>
&_Local/Makefile-_&<&'archtype'&>
&_Local/Makefile-_&<&'ostype'&>-<&'archtype'&>
&_OS/Makefile-Base_&
.endd
.cindex "&_Local/Makefile_&"
.cindex "building Exim" "operating system type"
.cindex "building Exim" "architecture type"
where <&'ostype'&> is the operating system type and <&'archtype'&> is the
architecture type. &_Local/Makefile_& is required to exist, and the building
process fails if it is absent. The other three &_Local_& files are optional,
and are often not needed.

The values used for <&'ostype'&> and <&'archtype'&> are obtained from scripts
called &_scripts/os-type_& and &_scripts/arch-type_& respectively. If either of
the environment variables EXIM_OSTYPE or EXIM_ARCHTYPE is set, their
values are used, thereby providing a means of forcing particular settings.
Otherwise, the scripts try to get values from the &%uname%& command. If this
fails, the shell variables OSTYPE and ARCHTYPE are inspected. A number
of &'ad hoc'& transformations are then applied, to produce the standard names
that Exim expects. You can run these scripts directly from the shell in order
to find out what values are being used on your system.


&_OS/Makefile-Default_& contains comments about the variables that are set
therein. Some (but not all) are mentioned below. If there is something that
needs changing, review the contents of this file and the contents of the make
file for your operating system (&_OS/Makefile-<ostype>_&) to see what the
default values are.


.cindex "building Exim" "overriding default settings"
If you need to change any of the values that are set in &_OS/Makefile-Default_&
or in &_OS/Makefile-<ostype>_&, or to add any new definitions, you do not
need to change the original files. Instead, you should make the changes by
putting the new values in an appropriate &_Local_& file. For example,
.cindex "Tru64-Unix build-time settings"
when building Exim in many releases of the Tru64-Unix (formerly Digital UNIX,
formerly DEC-OSF1) operating system, it is necessary to specify that the C
compiler is called &'cc'& rather than &'gcc'&. Also, the compiler must be
called with the option &%-std1%&, to make it recognize some of the features of
Standard C that Exim uses. (Most other compilers recognize Standard C by
default.) To do this, you should create a file called &_Local/Makefile-OSF1_&
containing the lines
.code
CC=cc
CFLAGS=-std1
.endd
If you are compiling for just one operating system, it may be easier to put
these lines directly into &_Local/Makefile_&.

Keeping all your local configuration settings separate from the distributed
files makes it easy to transfer them to new versions of Exim simply by copying
the contents of the &_Local_& directory.


.cindex "NIS lookup type" "including support for"
.cindex "NIS+ lookup type" "including support for"
.cindex "LDAP" "including support for"
.cindex "lookup" "inclusion in binary"
Exim contains support for doing LDAP, NIS, NIS+, and other kinds of file
lookup, but not all systems have these components installed, so the default is
not to include the relevant code in the binary. All the different kinds of file
and database lookup that Exim supports are implemented as separate code modules
which are included only if the relevant compile-time options are set. In the
case of LDAP, NIS, and NIS+, the settings for &_Local/Makefile_& are:
.code
LOOKUP_LDAP=yes
LOOKUP_NIS=yes
LOOKUP_NISPLUS=yes
.endd
and similar settings apply to the other lookup types. They are all listed in
&_src/EDITME_&. In many cases the relevant include files and interface
libraries need to be installed before compiling Exim.
.cindex "cdb" "including support for"
However, there are some optional lookup types (such as cdb) for which
the code is entirely contained within Exim, and no external include
files or libraries are required. When a lookup type is not included in the
binary, attempts to configure Exim to use it cause run time configuration
errors.

.cindex "pkg-config" "lookups"
.cindex "pkg-config" "authenticators"
Many systems now use a tool called &'pkg-config'& to encapsulate information
about how to compile against a library; Exim has some initial support for
being able to use pkg-config for lookups and authenticators.  For any given
makefile variable which starts &`LOOKUP_`& or &`AUTH_`&, you can add a new
variable with the &`_PC`& suffix in the name and assign as the value the
name of the package to be queried.  The results of querying via the
&'pkg-config'& command will be added to the appropriate Makefile variables
with &`+=`& directives, so your version of &'make'& will need to support that
syntax.  For instance:
.code
LOOKUP_SQLITE=yes
LOOKUP_SQLITE_PC=sqlite3
AUTH_GSASL=yes
AUTH_GSASL_PC=libgsasl
AUTH_HEIMDAL_GSSAPI=yes
AUTH_HEIMDAL_GSSAPI_PC=heimdal-gssapi
.endd

.cindex "Perl" "including support for"
Exim can be linked with an embedded Perl interpreter, allowing Perl
subroutines to be called during string expansion. To enable this facility,
.code
EXIM_PERL=perl.o
.endd
must be defined in &_Local/Makefile_&. Details of this facility are given in
chapter &<<CHAPperl>>&.

.cindex "X11 libraries, location of"
The location of the X11 libraries is something that varies a lot between
operating systems, and there may be different versions of X11 to cope
with. Exim itself makes no use of X11, but if you are compiling the Exim
monitor, the X11 libraries must be available.
The following three variables are set in &_OS/Makefile-Default_&:
.code
X11=/usr/X11R6
XINCLUDE=-I$(X11)/include
XLFLAGS=-L$(X11)/lib
.endd
These are overridden in some of the operating-system configuration files. For
example, in &_OS/Makefile-SunOS5_& there is
.code
X11=/usr/openwin
XINCLUDE=-I$(X11)/include
XLFLAGS=-L$(X11)/lib -R$(X11)/lib
.endd
If you need to override the default setting for your operating system, place a
definition of all three of these variables into your
&_Local/Makefile-<ostype>_& file.

.cindex "EXTRALIBS"
If you need to add any extra libraries to the link steps, these can be put in a
variable called EXTRALIBS, which appears in all the link commands, but by
default is not defined. In contrast, EXTRALIBS_EXIM is used only on the
command for linking the main Exim binary, and not for any associated utilities.

.cindex "DBM libraries" "configuration for building"
There is also DBMLIB, which appears in the link commands for binaries that
use DBM functions (see also section &<<SECTdb>>&). Finally, there is
EXTRALIBS_EXIMON, which appears only in the link step for the Exim monitor
binary, and which can be used, for example, to include additional X11
libraries.

.cindex "configuration file" "editing"
The make file copes with rebuilding Exim correctly if any of the configuration
files are edited. However, if an optional configuration file is deleted, it is
necessary to touch the associated non-optional file (that is,
&_Local/Makefile_& or &_Local/eximon.conf_&) before rebuilding.


.section "OS-specific header files" "SECID30"
.cindex "&_os.h_&"
.cindex "building Exim" "OS-specific C header files"
The &_OS_& directory contains a number of files with names of the form
&_os.h-<ostype>_&. These are system-specific C header files that should not
normally need to be changed. There is a list of macro settings that are
recognized in the file &_OS/os.configuring_&, which should be consulted if you
are porting Exim to a new operating system.



.section "Overriding build-time options for the monitor" "SECID31"
.cindex "building Eximon"
A similar process is used for overriding things when building the Exim monitor,
where the files that are involved are
.display
&_OS/eximon.conf-Default_&
&_OS/eximon.conf-_&<&'ostype'&>
&_Local/eximon.conf_&
&_Local/eximon.conf-_&<&'ostype'&>
&_Local/eximon.conf-_&<&'archtype'&>
&_Local/eximon.conf-_&<&'ostype'&>-<&'archtype'&>
.endd
.cindex "&_Local/eximon.conf_&"
As with Exim itself, the final three files need not exist, and in this case the
&_OS/eximon.conf-<ostype>_& file is also optional. The default values in
&_OS/eximon.conf-Default_& can be overridden dynamically by setting environment
variables of the same name, preceded by EXIMON_. For example, setting
EXIMON_LOG_DEPTH in the environment overrides the value of
LOG_DEPTH at run time.
.ecindex IIDbuex


.section "Installing Exim binaries and scripts" "SECID32"
.cindex "installing Exim"
.cindex "BIN_DIRECTORY"
The command &`make install`& runs the &(exim_install)& script with no
arguments. The script copies binaries and utility scripts into the directory
whose name is specified by the BIN_DIRECTORY setting in &_Local/Makefile_&.
.cindex "setuid" "installing Exim with"
The install script copies files only if they are newer than the files they are
going to replace. The Exim binary is required to be owned by root and have the
&'setuid'& bit set, for normal configurations. Therefore, you must run &`make
install`& as root so that it can set up the Exim binary in this way. However, in
some special situations (for example, if a host is doing no local deliveries)
it may be possible to run Exim without making the binary setuid root (see
chapter &<<CHAPsecurity>>& for details).

.cindex "CONFIGURE_FILE"
Exim's run time configuration file is named by the CONFIGURE_FILE setting
in &_Local/Makefile_&. If this names a single file, and the file does not
exist, the default configuration file &_src/configure.default_& is copied there
by the installation script. If a run time configuration file already exists, it
is left alone. If CONFIGURE_FILE is a colon-separated list, naming several
alternative files, no default is installed.

.cindex "system aliases file"
.cindex "&_/etc/aliases_&"
One change is made to the default configuration file when it is installed: the
default configuration contains a router that references a system aliases file.
The path to this file is set to the value specified by
SYSTEM_ALIASES_FILE in &_Local/Makefile_& (&_/etc/aliases_& by default).
If the system aliases file does not exist, the installation script creates it,
and outputs a comment to the user.

The created file contains no aliases, but it does contain comments about the
aliases a site should normally have. Mail aliases have traditionally been
kept in &_/etc/aliases_&. However, some operating systems are now using
&_/etc/mail/aliases_&. You should check if yours is one of these, and change
Exim's configuration if necessary.

The default configuration uses the local host's name as the only local domain,
and is set up to do local deliveries into the shared directory &_/var/mail_&,
running as the local user. System aliases and &_.forward_& files in users' home
directories are supported, but no NIS or NIS+ support is configured. Domains
other than the name of the local host are routed using the DNS, with delivery
over SMTP.

It is possible to install Exim for special purposes (such as building a binary
distribution) in a private part of the file system. You can do this by a
command such as
.code
make DESTDIR=/some/directory/ install
.endd
This has the effect of pre-pending the specified directory to all the file
paths, except the name of the system aliases file that appears in the default
configuration. (If a default alias file is created, its name &'is'& modified.)
For backwards compatibility, ROOT is used if DESTDIR is not set,
but this usage is deprecated.

.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.

For the utility programs, old versions are renamed by adding the suffix &_.O_&
to their names. The Exim binary itself, however, is handled differently. It is
installed under a name that includes the version number and the compile number,
for example &_exim-&version()-1_&. The script then arranges for a symbolic link
called &_exim_& to point to the binary. If you are updating a previous version
of Exim, the script takes care to ensure that the name &_exim_& is never absent
from the directory (as seen by other processes).

.cindex "installing Exim" "testing the script"
If you want to see what the &'make install'& will do before running it for
real, you can pass the &%-n%& option to the installation script by this
command:
.code
make INSTALL_ARG=-n install
.endd
The contents of the variable INSTALL_ARG are passed to the installation
script. You do not need to be root to run this test. Alternatively, you can run
the installation script directly, but this must be from within the build
directory. For example, from the top-level Exim directory you could use this
command:
.code
(cd build-SunOS5-5.5.1-sparc; ../scripts/exim_install -n)
.endd
.cindex "installing Exim" "install script options"
There are two other options that can be supplied to the installation script.

.ilist
&%-no_chown%& bypasses the call to change the owner of the installed binary
to root, and the call to make it a setuid binary.
.next
&%-no_symlink%& bypasses the setting up of the symbolic link &_exim_& to the
installed binary.
.endlist

INSTALL_ARG can be used to pass these options to the script. For example:
.code
make INSTALL_ARG=-no_symlink install
.endd
The installation script can also be given arguments specifying which files are
to be copied. For example, to install just the Exim binary, and nothing else,
without creating the symbolic link, you could use:
.code
make INSTALL_ARG='-no_symlink exim' install
.endd



.section "Installing info documentation" "SECTinsinfdoc"
.cindex "installing Exim" "&'info'& documentation"
Not all systems use the GNU &'info'& system for documentation, and for this
reason, the Texinfo source of Exim's documentation is not included in the main
distribution. Instead it is available separately from the ftp site (see section
&<<SECTavail>>&).

If you have defined INFO_DIRECTORY in &_Local/Makefile_& and the Texinfo
source of the documentation is found in the source tree, running &`make
install`& automatically builds the info files and installs them.



.section "Setting up the spool directory" "SECID33"
.cindex "spool directory" "creating"
When it starts up, Exim tries to create its spool directory if it does not
exist. The Exim uid and gid are used for the owner and group of the spool
directory. Sub-directories are automatically created in the spool directory as
necessary.




.section "Testing" "SECID34"
.cindex "testing" "installation"
Having installed Exim, you can check that the run time configuration file is
syntactically valid by running the following command, which assumes that the
Exim binary directory is within your PATH environment variable:
.code
exim -bV
.endd
If there are any errors in the configuration file, Exim outputs error messages.
Otherwise it outputs the version number and build date,
the DBM library that is being used, and information about which drivers and
other optional code modules are included in the binary.
Some simple routing tests can be done by using the address testing option. For
example,
.display
&`exim -bt`& <&'local username'&>
.endd
should verify that it recognizes a local mailbox, and
.display
&`exim -bt`& <&'remote address'&>
.endd
a remote one. Then try getting it to deliver mail, both locally and remotely.
This can be done by passing messages directly to Exim, without going through a
user agent. For example:
.code
exim -v postmaster@your.domain.example
From: user@your.domain.example
To: postmaster@your.domain.example
Subject: Testing Exim

This is a test message.
^D
.endd
The &%-v%& option causes Exim to output some verification of what it is doing.
In this case you should see copies of three log lines, one for the message's
arrival, one for its delivery, and one containing &"Completed"&.

.cindex "delivery" "problems with"
If you encounter problems, look at Exim's log files (&'mainlog'& and
&'paniclog'&) to see if there is any relevant information there. Another source
of information is running Exim with debugging turned on, by specifying the
&%-d%& option. If a message is stuck on Exim's spool, you can force a delivery
with debugging turned on by a command of the form
.display
&`exim -d -M`& <&'exim-message-id'&>
.endd
You must be root or an &"admin user"& in order to do this. The &%-d%& option
produces rather a lot of output, but you can cut this down to specific areas.
For example, if you use &%-d-all+route%& only the debugging information
relevant to routing is included. (See the &%-d%& option in chapter
&<<CHAPcommandline>>& for more details.)

.cindex '&"sticky"& bit'
.cindex "lock files"
One specific problem that has shown up on some sites is the inability to do
local deliveries into a shared mailbox directory, because it does not have the
&"sticky bit"& set on it. By default, Exim tries to create a lock file before
writing to a mailbox file, and if it cannot create the lock file, the delivery
is deferred. You can get round this either by setting the &"sticky bit"& on the
directory, or by setting a specific group for local deliveries and allowing
that group to create files in the directory (see the comments above the
&(local_delivery)& transport in the default configuration file). Another
approach is to configure Exim not to use lock files, but just to rely on
&[fcntl()]& locking instead. However, you should do this only if all user
agents also use &[fcntl()]& locking. For further discussion of locking issues,
see chapter &<<CHAPappendfile>>&.

One thing that cannot be tested on a system that is already running an MTA is
the receipt of incoming SMTP mail on the standard SMTP port. However, the
&%-oX%& option can be used to run an Exim daemon that listens on some other
port, or &'inetd'& can be used to do this. The &%-bh%& option and the
&'exim_checkaccess'& utility can be used to check out policy controls on
incoming SMTP mail.

Testing a new version on a system that is already running Exim can most easily
be done by building a binary with a different CONFIGURE_FILE setting. From
within the run time configuration, all other file and directory names
that Exim uses can be altered, in order to keep it entirely clear of the
production version.


.section "Replacing another MTA with Exim" "SECID35"
.cindex "replacing another MTA"
Building and installing Exim for the first time does not of itself put it in
general use. The name by which the system's MTA is called by mail user agents
is either &_/usr/sbin/sendmail_&, or &_/usr/lib/sendmail_& (depending on the
operating system), and it is necessary to make this name point to the &'exim'&
binary in order to get the user agents to pass messages to Exim. This is
normally done by renaming any existing file and making &_/usr/sbin/sendmail_&
or &_/usr/lib/sendmail_&
.cindex "symbolic link" "to &'exim'& binary"
a symbolic link to the &'exim'& binary. It is a good idea to remove any setuid
privilege and executable status from the old MTA. It is then necessary to stop
and restart the mailer daemon, if one is running.

.cindex "FreeBSD, MTA indirection"
.cindex "&_/etc/mail/mailer.conf_&"
Some operating systems have introduced alternative ways of switching MTAs. For
example, if you are running FreeBSD, you need to edit the file
&_/etc/mail/mailer.conf_& instead of setting up a symbolic link as just
described. A typical example of the contents of this file for running Exim is
as follows:
.code
sendmail            /usr/exim/bin/exim
send-mail           /usr/exim/bin/exim
mailq               /usr/exim/bin/exim -bp
newaliases          /usr/bin/true
.endd
Once you have set up the symbolic link, or edited &_/etc/mail/mailer.conf_&,
your Exim installation is &"live"&. Check it by sending a message from your
favourite user agent.

You should consider what to tell your users about the change of MTA. Exim may
have different capabilities to what was previously running, and there are
various operational differences such as the text of messages produced by
command line options and in bounce messages. If you allow your users to make
use of Exim's filtering capabilities, you should make the document entitled
&'Exim's interface to mail filtering'& available to them.



.section "Upgrading Exim" "SECID36"
.cindex "upgrading Exim"
If you are already running Exim on your host, building and installing a new
version automatically makes it available to MUAs, or any other programs that
call the MTA directly. However, if you are running an Exim daemon, you do need
to send it a HUP signal, to make it re-execute itself, and thereby pick up the
new binary. You do not need to stop processing mail in order to install a new
version of Exim. The install script does not modify an existing runtime
configuration file.




.section "Stopping the Exim daemon on Solaris" "SECID37"
.cindex "Solaris" "stopping Exim on"
The standard command for stopping the mailer daemon on Solaris is
.code
/etc/init.d/sendmail stop
.endd
If &_/usr/lib/sendmail_& has been turned into a symbolic link, this script
fails to stop Exim because it uses the command &'ps -e'& and greps the output
for the text &"sendmail"&; this is not present because the actual program name
(that is, &"exim"&) is given by the &'ps'& command with these options. A
solution is to replace the line that finds the process id with something like
.code
pid=`cat /var/spool/exim/exim-daemon.pid`
.endd
to obtain the daemon's pid directly from the file that Exim saves it in.

Note, however, that stopping the daemon does not &"stop Exim"&. Messages can
still be received from local processes, and if automatic delivery is configured
(the normal case), deliveries will still occur.




. ////////////////////////////////////////////////////////////////////////////
. ////////////////////////////////////////////////////////////////////////////

.chapter "The Exim command line" "CHAPcommandline"
.scindex IIDclo1 "command line" "options"
.scindex IIDclo2 "options" "command line"
Exim's command line takes the standard Unix form of a sequence of options,
each starting with a hyphen character, followed by a number of arguments. The
options are compatible with the main options of Sendmail, and there are also
some additional options, some of which are compatible with Smail 3. Certain
combinations of options do not make sense, and provoke an error if used.
The form of the arguments depends on which options are set.


.section "Setting options by program name" "SECID38"
.cindex "&'mailq'&"
If Exim is called under the name &'mailq'&, it behaves as if the option &%-bp%&
were present before any other options.
The &%-bp%& option requests a listing of the contents of the mail queue on the
standard output.
This feature is for compatibility with some systems that contain a command of
that name in one of the standard libraries, symbolically linked to
&_/usr/sbin/sendmail_& or &_/usr/lib/sendmail_&.

.cindex "&'rsmtp'&"
If Exim is called under the name &'rsmtp'& it behaves as if the option &%-bS%&
were present before any other options, for compatibility with Smail. The
&%-bS%& option is used for reading in a number of messages in batched SMTP
format.

.cindex "&'rmail'&"
If Exim is called under the name &'rmail'& it behaves as if the &%-i%& and
&%-oee%& options were present before any other options, for compatibility with
Smail. The name &'rmail'& is used as an interface by some UUCP systems.

.cindex "&'runq'&"
.cindex "queue runner"
If Exim is called under the name &'runq'& it behaves as if the option &%-q%&
were present before any other options, for compatibility with Smail. The &%-q%&
option causes a single queue runner process to be started.

.cindex "&'newaliases'&"
.cindex "alias file" "building"
.cindex "Sendmail compatibility" "calling Exim as &'newaliases'&"
If Exim is called under the name &'newaliases'& it behaves as if the option
&%-bi%& were present before any other options, for compatibility with Sendmail.
This option is used for rebuilding Sendmail's alias file. Exim does not have
the concept of a single alias file, but can be configured to run a given
command if called with the &%-bi%& option.


.section "Trusted and admin users" "SECTtrustedadmin"
Some Exim options are available only to &'trusted users'& and others are
available only to &'admin users'&. In the description below, the phrases &"Exim
user"& and &"Exim group"& mean the user and group defined by EXIM_USER and
EXIM_GROUP in &_Local/Makefile_& or set by the &%exim_user%& and
&%exim_group%& options. These do not necessarily have to use the name &"exim"&.

.ilist
.cindex "trusted users" "definition of"
.cindex "user" "trusted definition of"
The trusted users are root, the Exim user, any user listed in the
&%trusted_users%& configuration option, and any user whose current group or any
supplementary group is one of those listed in the &%trusted_groups%&
configuration option. Note that the Exim group is not automatically trusted.

.cindex '&"From"& line'
.cindex "envelope sender"
Trusted users are always permitted to use the &%-f%& option or a leading
&"From&~"& line to specify the envelope sender of a message that is passed to
Exim through the local interface (see the &%-bm%& and &%-f%& options below).
See the &%untrusted_set_sender%& option for a way of permitting non-trusted
users to set envelope senders.

.cindex "&'From:'& header line"
.cindex "&'Sender:'& header line"
.cindex "header lines" "From:"
.cindex "header lines" "Sender:"
For a trusted user, there is never any check on the contents of the &'From:'&
header line, and a &'Sender:'& line is never added. Furthermore, any existing
&'Sender:'& line in incoming local (non-TCP/IP) messages is not removed.

Trusted users may also specify a host name, host address, interface address,
protocol name, ident value, and authentication data when submitting a message
locally. Thus, they are able to insert messages into Exim's queue locally that
have the characteristics of messages received from a remote host. Untrusted
users may in some circumstances use &%-f%&, but can never set the other values
that are available to trusted users.
.next
.cindex "user" "admin definition of"
.cindex "admin user" "definition of"
The admin users are root, the Exim user, and any user that is a member of the
Exim group or of any group listed in the &%admin_groups%& configuration option.
The current group does not have to be one of these groups.

Admin users are permitted to list the queue, and to carry out certain
operations on messages, for example, to force delivery failures. It is also
necessary to be an admin user in order to see the full information provided by
the Exim monitor, and full debugging output.

By default, the use of the &%-M%&, &%-q%&, &%-R%&, and &%-S%& options to cause
Exim to attempt delivery of messages on its queue is restricted to admin users.
However, this restriction can be relaxed by setting the &%prod_requires_admin%&
option false (that is, specifying &%no_prod_requires_admin%&).

Similarly, the use of the &%-bp%& option to list all the messages in the queue
is restricted to admin users unless &%queue_list_requires_admin%& is set
false.
.endlist


&*Warning*&: If you configure your system so that admin users are able to
edit Exim's configuration file, you are giving those users an easy way of
getting root. There is further discussion of this issue at the start of chapter
&<<CHAPconf>>&.




.section "Command line options" "SECID39"
Exim's command line options are described in alphabetical order below. If none
of the options that specifies a specific action (such as starting the daemon or
a queue runner, or testing an address, or receiving a message in a specific
format, or listing the queue) are present, and there is at least one argument
on the command line, &%-bm%& (accept a local message on the standard input,
with the arguments specifying the recipients) is assumed. Otherwise, Exim
outputs a brief message about itself and exits.

. ////////////////////////////////////////////////////////////////////////////
. Insert a stylized XML comment here, to identify the start of the command line
. options. This is for the benefit of the Perl script that automatically
. creates a man page for the options.
. ////////////////////////////////////////////////////////////////////////////

.literal xml
<!-- === Start of command line options === -->
.literal off


.vlist
.vitem &%--%&
.oindex "--"
.cindex "options" "command line; terminating"
This is a pseudo-option whose only purpose is to terminate the options and
therefore to cause subsequent command line items to be treated as arguments
rather than options, even if they begin with hyphens.

.vitem &%--help%&
.oindex "&%--help%&"
This option causes Exim to output a few sentences stating what it is.
The same output is generated if the Exim binary is called with no options and
no arguments.

.vitem &%--version%&
.oindex "&%--version%&"
This option is an alias for &%-bV%& and causes version information to be
displayed.

.vitem &%-Ac%& &&&
       &%-Am%&
.oindex "&%-Ac%&"
.oindex "&%-Am%&"
These options are used by Sendmail for selecting configuration files and are
ignored by Exim.

.vitem &%-B%&<&'type'&>
.oindex "&%-B%&"
.cindex "8-bit characters"
.cindex "Sendmail compatibility" "8-bit characters"
This is a Sendmail option for selecting 7 or 8 bit processing. Exim is 8-bit
clean; it ignores this option.

.vitem &%-bd%&
.oindex "&%-bd%&"
.cindex "daemon"
.cindex "SMTP" "listener"
.cindex "queue runner"
This option runs Exim as a daemon, awaiting incoming SMTP connections. Usually
the &%-bd%& option is combined with the &%-q%&<&'time'&> option, to specify
that the daemon should also initiate periodic queue runs.

The &%-bd%& option can be used only by an admin user. If either of the &%-d%&
(debugging) or &%-v%& (verifying) options are set, the daemon does not
disconnect from the controlling terminal. When running this way, it can be
stopped by pressing ctrl-C.

By default, Exim listens for incoming connections to the standard SMTP port on
all the host's running interfaces. However, it is possible to listen on other
ports, on multiple ports, and only on specific interfaces. Chapter
&<<CHAPinterfaces>>& contains a description of the options that control this.

When a listening daemon
.cindex "daemon" "process id (pid)"
.cindex "pid (process id)" "of daemon"
is started without the use of &%-oX%& (that is, without overriding the normal
configuration), it writes its process id to a file called &_exim-daemon.pid_&
in Exim's spool directory. This location can be overridden by setting
PID_FILE_PATH in &_Local/Makefile_&. The file is written while Exim is still
running as root.

When &%-oX%& is used on the command line to start a listening daemon, the
process id is not written to the normal pid file path. However, &%-oP%& can be
used to specify a path on the command line if a pid file is required.

The SIGHUP signal
.cindex "SIGHUP"
.cindex "daemon" "restarting"
can be used to cause the daemon to re-execute itself. This should be done
whenever Exim's configuration file, or any file that is incorporated into it by
means of the &%.include%& facility, is changed, and also whenever a new version
of Exim is installed. It is not necessary to do this when other files that are
referenced from the configuration (for example, alias files) are changed,
because these are reread each time they are used.

.vitem &%-bdf%&
.oindex "&%-bdf%&"
This option has the same effect as &%-bd%& except that it never disconnects
from the controlling terminal, even when no debugging is specified.

.vitem &%-be%&
.oindex "&%-be%&"
.cindex "testing" "string expansion"
.cindex "expansion" "testing"
Run Exim in expansion testing mode. Exim discards its root privilege, to
prevent ordinary users from using this mode to read otherwise inaccessible
files. If no arguments are given, Exim runs interactively, prompting for lines
of data. Otherwise, it processes each argument in turn.

If Exim was built with USE_READLINE=yes in &_Local/Makefile_&, it tries
to load the &%libreadline%& library dynamically whenever the &%-be%& option is
used without command line arguments. If successful, it uses the &[readline()]&
function, which provides extensive line-editing facilities, for reading the
test data. A line history is supported.

Long expansion expressions can be split over several lines by using backslash
continuations. As in Exim's run time configuration, white space at the start of
continuation lines is ignored. Each argument or data line is passed through the
string expansion mechanism, and the result is output. Variable values from the
configuration file (for example, &$qualify_domain$&) are available, but no
message-specific values (such as &$message_exim_id$&) are set, because no message
is being processed (but see &%-bem%& and &%-Mset%&).

&*Note*&: If you use this mechanism to test lookups, and you change the data
files or databases you are using, you must exit and restart Exim before trying
the same lookup again. Otherwise, because each Exim process caches the results
of lookups, you will just get the same result as before.

Macro processing is done on lines before string-expansion: new macros can be
defined and macros will be expanded.
Because macros in the config file are often used for secrets, those are only
available to admin users.

.vitem &%-bem%&&~<&'filename'&>
.oindex "&%-bem%&"
.cindex "testing" "string expansion"
.cindex "expansion" "testing"
This option operates like &%-be%& except that it must be followed by the name
of a file. For example:
.code
exim -bem /tmp/testmessage
.endd
The file is read as a message (as if receiving a locally-submitted non-SMTP
message) before any of the test expansions are done. Thus, message-specific
variables such as &$message_size$& and &$header_from:$& are available. However,
no &'Received:'& header is added to the message. If the &%-t%& option is set,
recipients are read from the headers in the normal way, and are shown in the
&$recipients$& variable. Note that recipients cannot be given on the command
line, because further arguments are taken as strings to expand (just like
&%-be%&).

.vitem &%-bF%&&~<&'filename'&>
.oindex "&%-bF%&"
.cindex "system filter" "testing"
.cindex "testing" "system filter"
This option is the same as &%-bf%& except that it assumes that the filter being
tested is a system filter. The additional commands that are available only in
system filters are recognized.

.vitem &%-bf%&&~<&'filename'&>
.oindex "&%-bf%&"
.cindex "filter" "testing"
.cindex "testing" "filter file"
.cindex "forward file" "testing"
.cindex "testing" "forward file"
.cindex "Sieve filter" "testing"
This option runs Exim in user filter testing mode; the file is the filter file
to be tested, and a test message must be supplied on the standard input. If
there are no message-dependent tests in the filter, an empty file can be
supplied.

If you want to test a system filter file, use &%-bF%& instead of &%-bf%&. You
can use both &%-bF%& and &%-bf%& on the same command, in order to test a system
filter and a user filter in the same run. For example:
.code
exim -bF /system/filter -bf /user/filter </test/message
.endd
This is helpful when the system filter adds header lines or sets filter
variables that are used by the user filter.

If the test filter file does not begin with one of the special lines
.code
# Exim filter
# Sieve filter
.endd
it is taken to be a normal &_.forward_& file, and is tested for validity under
that interpretation. See sections &<<SECTitenonfilred>>& to
&<<SECTspecitredli>>& for a description of the possible contents of non-filter
redirection lists.

The result of an Exim command that uses &%-bf%&, provided no errors are
detected, is a list of the actions that Exim would try to take if presented
with the message for real. More details of filter testing are given in the
separate document entitled &'Exim's interfaces to mail filtering'&.

When testing a filter file,
.cindex "&""From""& line"
.cindex "envelope sender"
.oindex "&%-f%&" "for filter testing"
the envelope sender can be set by the &%-f%& option,
or by a &"From&~"& line at the start of the test message. Various parameters
that would normally be taken from the envelope recipient address of the message
can be set by means of additional command line options (see the next four
options).

.vitem &%-bfd%&&~<&'domain'&>
.oindex "&%-bfd%&"
.vindex "&$qualify_domain$&"
This sets the domain of the recipient address when a filter file is being
tested by means of the &%-bf%& option. The default is the value of
&$qualify_domain$&.

.vitem &%-bfl%&&~<&'local&~part'&>
.oindex "&%-bfl%&"
This sets the local part of the recipient address when a filter file is being
tested by means of the &%-bf%& option. The default is the username of the
process that calls Exim. A local part should be specified with any prefix or
suffix stripped, because that is how it appears to the filter when a message is
actually being delivered.

.vitem &%-bfp%&&~<&'prefix'&>
.oindex "&%-bfp%&"
This sets the prefix of the local part of the recipient address when a filter
file is being tested by means of the &%-bf%& option. The default is an empty
prefix.

.vitem &%-bfs%&&~<&'suffix'&>
.oindex "&%-bfs%&"
This sets the suffix of the local part of the recipient address when a filter
file is being tested by means of the &%-bf%& option. The default is an empty
suffix.

.vitem &%-bh%&&~<&'IP&~address'&>
.oindex "&%-bh%&"
.cindex "testing" "incoming SMTP"
.cindex "SMTP" "testing incoming"
.cindex "testing" "relay control"
.cindex "relaying" "testing configuration"
.cindex "policy control" "testing"
.cindex "debugging" "&%-bh%& option"
This option runs a fake SMTP session as if from the given IP address, using the
standard input and output. The IP address may include a port number at the end,
after a full stop. For example:
.code
exim -bh 10.9.8.7.1234
exim -bh fe80::a00:20ff:fe86:a061.5678
.endd
When an IPv6 address is given, it is converted into canonical form. In the case
of the second example above, the value of &$sender_host_address$& after
conversion to the canonical form is
&`fe80:0000:0000:0a00:20ff:fe86:a061.5678`&.

Comments as to what is going on are written to the standard error file. These
include lines beginning with &"LOG"& for anything that would have been logged.
This facility is provided for testing configuration options for incoming
messages, to make sure they implement the required policy. For example, you can
test your relay controls using &%-bh%&.

&*Warning 1*&:
.cindex "RFC 1413"
You can test features of the configuration that rely on ident (RFC 1413)
information by using the &%-oMt%& option. However, Exim cannot actually perform
an ident callout when testing using &%-bh%& because there is no incoming SMTP
connection.

&*Warning 2*&: Address verification callouts (see section &<<SECTcallver>>&)
are also skipped when testing using &%-bh%&. If you want these callouts to
occur, use &%-bhc%& instead.

Messages supplied during the testing session are discarded, and nothing is
written to any of the real log files. There may be pauses when DNS (and other)
lookups are taking place, and of course these may time out. The &%-oMi%& option
can be used to specify a specific IP interface and port if this is important,
and &%-oMaa%& and &%-oMai%& can be used to set parameters as if the SMTP
session were authenticated.

The &'exim_checkaccess'& utility is a &"packaged"& version of &%-bh%& whose
output just states whether a given recipient address from a given host is
acceptable or not. See section &<<SECTcheckaccess>>&.

Features such as authentication and encryption, where the client input is not
plain text, cannot easily be tested with &%-bh%&. Instead, you should use a
specialized SMTP test program such as
&url(http://jetmore.org/john/code/#swaks,swaks).

.vitem &%-bhc%&&~<&'IP&~address'&>
.oindex "&%-bhc%&"
This option operates in the same way as &%-bh%&, except that address
verification callouts are performed if required. This includes consulting and
updating the callout cache database.

.vitem &%-bi%&
.oindex "&%-bi%&"
.cindex "alias file" "building"
.cindex "building alias file"
.cindex "Sendmail compatibility" "&%-bi%& option"
Sendmail interprets the &%-bi%& option as a request to rebuild its alias file.
Exim does not have the concept of a single alias file, and so it cannot mimic
this behaviour. However, calls to &_/usr/lib/sendmail_& with the &%-bi%& option
tend to appear in various scripts such as NIS make files, so the option must be
recognized.

If &%-bi%& is encountered, the command specified by the &%bi_command%&
configuration option is run, under the uid and gid of the caller of Exim. If
the &%-oA%& option is used, its value is passed to the command as an argument.
The command set by &%bi_command%& may not contain arguments. The command can
use the &'exim_dbmbuild'& utility, or some other means, to rebuild alias files
if this is required. If the &%bi_command%& option is not set, calling Exim with
&%-bi%& is a no-op.

. // Keep :help first, then the rest in alphabetical order
.vitem &%-bI:help%&
.oindex "&%-bI:help%&"
.cindex "querying exim information"
We shall provide various options starting &`-bI:`& for querying Exim for
information.  The output of many of these will be intended for machine
consumption.  This one is not.  The &%-bI:help%& option asks Exim for a
synopsis of supported options beginning &`-bI:`&.  Use of any of these
options shall cause Exim to exit after producing the requested output.

.vitem &%-bI:dscp%&
.oindex "&%-bI:dscp%&"
.cindex "DSCP" "values"
This option causes Exim to emit an alphabetically sorted list of all
recognised DSCP names.

.vitem &%-bI:sieve%&
.oindex "&%-bI:sieve%&"
.cindex "Sieve filter" "capabilities"
This option causes Exim to emit an alphabetically sorted list of all supported
Sieve protocol extensions on stdout, one per line.  This is anticipated to be
useful for ManageSieve (RFC 5804) implementations, in providing that protocol's
&`SIEVE`& capability response line.  As the precise list may depend upon
compile-time build options, which this option will adapt to, this is the only
way to guarantee a correct response.

.vitem &%-bm%&
.oindex "&%-bm%&"
.cindex "local message reception"
This option runs an Exim receiving process that accepts an incoming,
locally-generated message on the standard input. The recipients are given as the
command arguments (except when &%-t%& is also present &-- see below). Each
argument can be a comma-separated list of RFC 2822 addresses. This is the
default option for selecting the overall action of an Exim call; it is assumed
if no other conflicting option is present.

If any addresses in the message are unqualified (have no domain), they are
qualified by the values of the &%qualify_domain%& or &%qualify_recipient%&
options, as appropriate. The &%-bnq%& option (see below) provides a way of
suppressing this for special cases.

Policy checks on the contents of local messages can be enforced by means of
the non-SMTP ACL. See chapter &<<CHAPACL>>& for details.

.cindex "return code" "for &%-bm%&"
The return code is zero if the message is successfully accepted. Otherwise, the
action is controlled by the &%-oe%&&'x'& option setting &-- see below.

The format
.cindex "message" "format"
.cindex "format" "message"
.cindex "&""From""& line"
.cindex "UUCP" "&""From""& line"
.cindex "Sendmail compatibility" "&""From""& line"
of the message must be as defined in RFC 2822, except that, for
compatibility with Sendmail and Smail, a line in one of the forms
.code
From sender Fri Jan  5 12:55 GMT 1997
From sender Fri, 5 Jan 97 12:55:01
.endd
(with the weekday optional, and possibly with additional text after the date)
is permitted to appear at the start of the message. There appears to be no
authoritative specification of the format of this line. Exim recognizes it by
matching against the regular expression defined by the &%uucp_from_pattern%&