-. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.26 2007/10/24 17:47:31 fanf2 Exp $
+. $Cambridge: exim/doc/doc-docbook/spec.xfpt,v 1.27 2007/12/01 15:53:55 nm4 Exp $
.
. /////////////////////////////////////////////////////////////////////////////
. This is the primary source of the Exim Manual. It is an xfpt document that is
. the <bookinfo> element must also be updated for each new edition.
. /////////////////////////////////////////////////////////////////////////////
-.set previousversion "4.67"
-.set version "4.68"
+.set previousversion "4.68"
+.set version "4.69"
.set ACL "access control lists (ACLs)"
.set I " "
lists.
.section "Exim training" "SECID4"
-.new
.cindex "training courses"
Training courses in Cambridge (UK) used to be run annually by the author of
Exim, before he retired. At the time of writing, there are no plans to run
further Exim courses in Cambridge. However, if that changes, relevant
information will be posted at &url(http://www-tus.csx.cam.ac.uk/courses/exim/).
-.wen
.section "Bug reports" "SECID5"
.cindex "bug reports"
This option causes the contents of the message body (-D) spool file to be
written to the standard output. This option can be used only by an admin user.
-.new
.vitem &%-Mvc%&&~<&'message&~id'&>
.oindex "&%-Mvc%&"
.cindex "message" "listing in RFC 2822 format"
This option causes a copy of the complete message (header lines plus body) to
be written to the standard output in RFC 2822 format. This option can be used
only by an admin user.
-.wen
.vitem &%-Mvh%&&~<&'message&~id'&>
.oindex "&%-Mvh%&"
define mechanisms for copying messages to destinations (see chapters
&<<CHAPtransportgeneric>>&&--&<<CHAPsmtptrans>>&).
.next
-.new
&'retry'&: Retry rules, for use when a message cannot be delivered immediately.
If there is no retry section, or if it is empty (that is, no retry rules are
defined), Exim will not retry deliveries. In this situation, temporary errors
are treated the same as permanent errors. Retry rules are discussed in chapter
&<<CHAPretry>>&.
-.wen
.next
&'rewrite'&: Global address rewriting rules, for use when a message arrives and
when new addresses are generated during delivery. Rewriting is discussed in
1.5 until 16 hours have passed, then every 6 hours up to 4 days. If an address
is not delivered after 4 days of temporary failure, it is bounced.
-.new
If the retry section is removed from the configuration, or is empty (that is,
if no retry rules are defined), Exim will not retry deliveries. This turns
temporary errors into permanent errors.
-.wen
.section "Rewriting configuration" "SECID58"
utility program for creating DBM files (&'exim_dbmbuild'&) includes the zeros
by default, but has an option to omit them (see section &<<SECTdbmbuild>>&).
.next
-.new
.cindex "lookup" "dsearch"
.cindex "dsearch lookup type"
&(dsearch)&: The given file must be a directory; this is searched for an entry
symbolic link, or any other kind of directory entry. An example of how this
lookup can be used to support virtual domains is given in section
&<<SECTvirtualdomains>>&.
-.wen
.next
.cindex "lookup" "iplsearch"
.cindex "iplsearch lookup type"
hide mysql_servers = localhost/users/root/secret:\
otherhost/users/root/othersecret
.endd
-.new
For MySQL and PostgreSQL, a host may be specified as <&'name'&>:<&'port'&> but
because this is a colon-separated list, the colon has to be doubled. For each
query, these parameter groups are tried in order until a connection is made and
a query is successfully processed. The result of a query may be that no data is
found, but that is still a successful query. In other words, the list of
servers provides a backup facility, not a list of different places to look.
-.wen
The &%quote_mysql%&, &%quote_pgsql%&, and &%quote_oracle%& expansion operators
convert newline, tab, carriage return, and backspace to \n, \t, \r, and \b
for MySQL because these escapes are not recognized in contexts where these
characters are not special.
-.new
.section "Specifying the server in the query" "SECTspeserque"
For MySQL and PostgreSQL lookups (but not currently for Oracle and InterBase),
it is possible to specify a list of servers with an individual query. This is
.code
${lookup pgsql{servers=master/db/name/pw; UPDATE ...}
.endd
-.wen
.section "Special MySQL features" "SECID73"
possible to use the same configuration file on several different hosts that
differ only in their names.
.next
-.new
.cindex "@[] in a domain list"
.cindex "domain list" "matching local IP interfaces"
.cindex "domain literal"
&%local_interfaces%& and &%extra_local_interfaces%& options can be used to
control which of a host's several IP addresses are treated as local.
In today's Internet, the use of domain literals is controversial.
-.wen
.next
.cindex "@mx_any"
.cindex "@mx_primary"
&'cipher.key.ex'&.
.next
-.new
.cindex "regular expressions" "in domain list"
.cindex "domain list" "matching regular expression"
If a pattern starts with a circumflex character, it is treated as a regular
default case-independent, but you can make it case-dependent by starting it
with &`(?-i)`&. References to descriptions of the syntax of regular expressions
are given in chapter &<<CHAPregexp>>&.
-.wen
&*Warning*&: Because domain lists are expanded before being processed, you
must escape any backslash and dollar characters in the regular expression, or
is 192.168.34.6, the key that is looked up for the above example is
&"192.168.34.0/24"&.
-.new
When an IPv6 address is converted to a string, dots are normally used instead
of colons, so that keys in &(lsearch)& files need not contain colons (which
terminate &(lsearch)& keys). This was implemented some time before the ability
colons in all cases, given that quoting is now available for &(lsearch)&.
However, this would be an incompatible change that might break some existing
configurations.
-.wen
&*Warning*&: Specifying &%net32-%& (for an IPv4 address) or &%net128-%& (for an
IPv6 address) is not the same as specifying just &%net-%& without a number. In
requirement. Other kinds of wildcarding require the use of a regular
expression.
.next
-.new
.cindex "regular expressions" "in host list"
.cindex "host list" "regular expression in"
If the item starts with &"^"& it is taken to be a regular expression which is
case-dependent by starting it with &`(?-i)`&. References to descriptions of the
syntax of regular expressions are given in chapter &<<CHAPregexp>>&. For
example,
-.wen
.code
^(a|b)\.c\.d$
.endd
from an IP address (see section &<<SECThoslispatnam>>&). In either case, the
behaviour when it fails to find the information it is seeking is the same.
-.new
&*Note*&: This section applies to permanent lookup failures. It does &'not'&
apply to temporary DNS errors, whose handling is described in the next section.
-.wen
.cindex "&`+include_unknown`&"
.cindex "&`+ignore_unknown`&"
list.
-.new
.section "Temporary DNS errors when looking up host information" &&&
"SECTtemdnserr"
.cindex "host" "lookup failures, temporary"
&`+ignore_unknown`& and &`+include_unknown`&, as described in the previous
section. These options should be used with care, probably only in non-critical
host lists such as whitelists.
-.wen
character set defined by &%headers_charset%&. Overlong RFC 2047 &"words"& are
not recognized unless &%check_rfc2047_length%& is set false.
-.new
&*Note*&: If you use &%$header%&_&'xxx'&&*:*& (or &%$h%&_&'xxx'&&*:*&) to
access a header line, RFC 2047 decoding is done automatically. You do not need
to use this operator as well.
-.wen
an IP address. Both IPv4 and IPv6 addresses are valid for &%isip%&, whereas
&%isip4%& and &%isip6%& test specifically for IPv4 or IPv6 addresses.
-.new
For an IPv4 address, the test is for four dot-separated components, each of
which consists of from one to three digits. For an IPv6 address, up to eight
colon-separated components are permitted, each containing from one to four
${if isip4{$sender_host_address}...
.endd
to test which IP version an incoming SMTP connection is using.
-.wen
.vitem &*ldapauth&~{*&<&'ldap&~query'&>&*}*&
.cindex "LDAP" "use for authentication"
content-scanning extension and the obsolete &%demime%& condition. For details,
see section &<<SECTdemimecond>>&.
-.new
.vitem &$dnslist_domain$& &&&
&$dnslist_matched$& &&&
&$dnslist_text$& &&&
the following data from the lookup: the list's domain name, the key that was
looked up, the contents of any associated TXT record, and the value from the
main A record. See section &<<SECID204>>& for more details.
-.wen
.vitem &$domain$&
.vindex "&$domain$&"
content-scanning extension. It is set to the name of the virus that was found
when the ACL &%malware%& condition is true (see section &<<SECTscanvirus>>&).
-.new
.vitem &$max_received_linelength$&
.vindex "&$max_received_linelength$&"
.cindex "maximum" "line length"
This variable contains the number of bytes in the longest line that was
received as part of the message, not counting the line termination
character(s).
-.wen
.vitem &$message_age$&
.cindex "message" "age of"
number of characters of the body that are put into the variable is set by the
&%message_body_visible%& configuration option; the default is 500.
-.new
.oindex "&%message_body_newlines%&"
By default, newlines are converted into spaces in &$message_body$&, to make it
easier to search for phrases that might be split over a line break. However,
this can be disabled by setting &%message_body_newlines%& to be true. Binary
zeros are always converted into spaces.
-.wen
.vitem &$message_body_end$&
.cindex "body of message" "expansion variable"
message was received, and &"0"& otherwise.
.vitem &$tls_cipher$&
-.new
.vindex "&$tls_cipher$&"
When a message is received from a remote host over an encrypted SMTP
connection, this variable is set to the cipher suite that was negotiated, for
and then set to the outgoing cipher suite if one is negotiated. See chapter
&<<CHAPTLS>>& for details of TLS support and chapter &<<CHAPsmtptrans>>& for
details of the &(smtp)& transport.
-.wen
.vitem &$tls_peerdn$&
.vindex "&$tls_peerdn$&"
interfaces and recognizing the local host.
-.new
.option ibase_servers main "string list" unset
.cindex "InterBase" "server list"
This option provides a list of InterBase servers and associated connection data,
to be used in conjunction with &(ibase)& lookups (see section &<<SECID72>>&).
The option is available only if Exim has been built with InterBase support.
-.wen
an argument that is longer behaves as if &[getpwnam()]& failed.
-.new
.option message_body_newlines main bool false
.cindex "message body" "newlines in variables"
.cindex "newline" "in message body variables"
By default, newlines in the message body are replaced by spaces when setting
the &$message_body$& and &$message_body_end$& expansion variables. If this
option is set true, this no longer happens.
-.wen
.option message_body_visible main integer 500
.option queue_only_load main fixed-point unset
-.new
.cindex "load average"
.cindex "queueing incoming messages"
.cindex "message" "queueing by load"
the same SMTP connection are queued by default, whatever happens to the load in
the meantime, but this can be changed by setting &%queue_only_load_latch%&
false.
-.wen
Deliveries will subsequently be performed by queue runner processes. This
option has no effect on ancient operating systems on which Exim cannot
&%smtp_load_reserve%&.
-.new
.option queue_only_load_latch main boolean true
.cindex "load average" "re-evaluating per message"
When this option is true (the default), once one message has been queued
where this is not the best strategy. In such cases, &%queue_only_load_latch%&
should be set false. This causes the value of the load average to be
re-evaluated for each message.
-.wen
.option queue_only_override main boolean true
.option smtp_accept_queue main integer 0
-.new
.cindex "SMTP" "incoming connection count"
.cindex "queueing incoming messages"
.cindex "message" "queueing by SMTP connection count"
fixed at the start of an SMTP connection. It cannot be updated in the
subprocess that receives messages, and so the queueing or not queueing applies
to all messages received in the same connection.
-.wen
A value of zero implies no limit, and clearly any non-zero value is useful only
if it is less than the &%smtp_accept_max%& value (unless that is zero). See
either &%tls_verify_hosts%& or &%tls_try_verify_hosts%& is set and
&%tls_verify_certificates%& is not set.
-.new
Any client that matches &%tls_verify_hosts%& is constrained by
&%tls_verify_certificates%&. When the client initiates a TLS session, it must
present one of the listed certificates. If it does not, the connection is
the host to use TLS. It can still send SMTP commands through unencrypted
connections. Forcing a client to use TLS has to be done separately using an
ACL to reject inappropriate commands when the connection is not encrypted.
-.wen
A weaker form of checking is provided by &%tls_try_verify_hosts%&. If a client
matches this option (but not &%tls_verify_hosts%&), Exim requests a
check_local_user
transport = local_delivery
.endd
-.new
For security, it would probably be a good idea to restrict the use of this
router to locally-generated messages, using a condition such as this:
.code
condition = ${if match {$sender_host_address}\
{\N^(|127\.0\.0\.1)$\N}}
.endd
-.wen
If both &%local_part_prefix%& and &%local_part_suffix%& are set for a router,
both conditions must be met if not optional. Care must be taken if wildcards
.option pass_router routers string unset
-.new
.cindex "router" "go to after &""pass""&"
Routers that recognize the generic &%self%& option (&(dnslookup)&,
&(ipliteral)&, and &(manualroute)&) are able to return &"pass"&, forcing
be below the current router, to avoid loops. Note that this option applies only
to the special case of &"pass"&. It does not apply when a router returns
&"decline"& because it cannot handle an address.
-.wen
local_part_prefix = real-
transport = local_delivery
.endd
-.new
For security, it would probably be a good idea to restrict the use of this
router to locally-generated messages, using a condition such as this:
.code
condition = ${if match {$sender_host_address}\
{\N^(|127\.0\.0\.1)$\N}}
.endd
-.wen
.option syntax_errors_text redirect string&!! unset
message_prefix = "From ${if def:return_path{$return_path}\
{MAILER-DAEMON}} $tod_bsdinbox\n"
.endd
-.new
&*Note:*& If you set &%use_crlf%& true, you must change any occurrences of
&`\n`& to &`\r\n`& in &%message_prefix%&.
-.wen
.option message_suffix appendfile string&!! "see below"
The string specified here is expanded and output at the end of every message.
.code
message_suffix =
.endd
-.new
&*Note:*& If you set &%use_crlf%& true, you must change any occurrences of
&`\n`& to &`\r\n`& in &%message_suffix%&.
-.wen
.option mode appendfile "octal integer" 0600
If the output file is created, it is given this mode. If it already exists and
of batched SMTP, the byte sequence written to the file is then an exact image
of what would be sent down a real SMTP connection.
-.new
&*Note:*& The contents of the &%message_prefix%& and &%message_suffix%& options
(which are used to supply the traditional &"From&~"& and blank line separators
in Berkeley-style mailboxes) are written verbatim, so must contain their own
carriage return characters if these are needed. In cases where these options
have non-empty defaults, the values end with a single linefeed, so they must be
changed to end with &`\r\n`& if &%use_crlf%& is set.
-.wen
.option use_fcntl_lock appendfile boolean "see below"
.code
message_prefix =
.endd
-.new
&*Note:*& If you set &%use_crlf%& true, you must change any occurrences of
&`\n`& to &`\r\n`& in &%message_prefix%&.
-.wen
.option message_suffix pipe string&!! "see below"
.code
message_suffix =
.endd
-.new
&*Note:*& If you set &%use_crlf%& true, you must change any occurrences of
&`\n`& to &`\r\n`& in &%message_suffix%&.
-.wen
.option path pipe string "see below"
of batched SMTP, the byte sequence written to the pipe is then an exact image
of what would be sent down a real SMTP connection.
-.new
The contents of the &%message_prefix%& and &%message_suffix%& options are
written verbatim, so must contain their own carriage return characters if these
are needed. When &%use_bsmtp%& is not set, the default values for both
&%message_prefix%& and &%message_suffix%& end with a single linefeed, so their
values must be changed to end with &`\r\n`& if &%use_crlf%& is set.
-.wen
.option use_shell pipe boolean false
&%serialize_hosts%&, and the various TLS options are expanded.
-.new
.section "Use of $tls_cipher and $tls_peerdn" "usecippeer"
.vindex &$tls_cipher$&
.vindex &$tls_peerdn$&
appropriate values for the outgoing connection, and these are the values that
are in force when any authenticators are run and when the
&%authenticated_sender%& option is expanded.
-.wen
.section "Private options for smtp" "SECID146"
to be deferred. If the result of expansion is an empty string, that is also
ignored.
-.new
The expansion happens after the outgoing connection has been made and TLS
started, if required. This means that the &$host$&, &$host_address$&,
&$tls_cipher$&, and &$tls_peerdn$& variables are set according to the
particular connection.
-.wen
If the SMTP session is not authenticated, the expansion of
&%authenticated_sender%& still happens (and can cause the delivery to be
&`s`& rewrite the &'Sender:'& header
&`t`& rewrite the &'To:'& header
.endd
+.new
"All headers" means all of the headers listed above that can be selected
individually, plus their &'Resent-'& versions. It does not include
other headers such as &'Subject:'& etc.
+.wen
You should be particularly careful about rewriting &'Sender:'& headers, and
restrict this to special known cases in your own domains.
.chapter "Retry configuration" "CHAPretry"
.scindex IIDretconf1 "retry" "configuration, description of"
.scindex IIDregconf2 "configuration file" "retry section"
-.new
The &"retry"& section of the runtime configuration file contains a list of
retry rules that control how often Exim tries to deliver messages that cannot
be delivered at the first attempt. If there are no retry rules (the section is
general-purpose retry rule (see section &<<SECID57>>&). The &%-brt%& command
line option can be used to test which retry rule will be used for a given
address, domain and error.
-.wen
The most common cause of retries is temporary failure to deliver to a remote
host because the host is down, or inaccessible because of a network problem.
.cindex "authentication" "generic options"
.cindex "options" "generic; for authenticators"
-.new
.option client_condition authenticators string&!! unset
When Exim is authenticating as a client, it skips any authenticator whose
&%client_condition%& expansion yields &"0"&, &"no"&, or &"false"&. This can be
(Older documentation incorrectly states that &$tls_cipher$& contains the cipher
used for incoming messages. In fact, during SMTP delivery, it contains the
cipher used for the delivery.)
-.wen
.option driver authenticators string unset
&new("(For outgoing SMTP deliveries, &$tls_cipher$& is reset &-- see section
&<<SECID185>>&.)")
-.new
Once TLS has been established, the ACLs that run for subsequent SMTP commands
can check the name of the cipher suite and vary their actions accordingly. The
cipher suite names vary, depending on which TLS library is being used. For
example, OpenSSL uses the name DES-CBC3-SHA for the cipher suite which in other
contexts is known as TLS_RSA_WITH_3DES_EDE_CBC_SHA. Check the OpenSSL or GnuTLS
documentation for more details.
-.wen
.section "Requesting and verifying client certificates" "SECID183"
which the client is connected. Forced failure of an expansion causes Exim to
behave as if the relevant option were unset.
-.new
.vindex &$tls_cipher$&
.vindex &$tls_peerdn$&
Before an SMTP connection is established, the &$tls_cipher$& and &$tls_peerdn$&
that were set when the message was received.) If STARTTLS is subsequently
successfully obeyed, these variables are set to the relevant values for the
outgoing connection.
-.wen
-.new
.section "The not-QUIT ACL" "SECTNOTQUITACL"
The not-QUIT ACL, specified by &%smtp_notquit_acl%&, is run in most cases when
an SMTP session ends without sending QUIT. However, when Exim itself is is bad
overridden by the &%message%& modifier in the not-QUIT ACL. In the case of a
&%drop%& verb in another ACL, it is the message from the other ACL that is
used.
-.wen
.section "Finding an ACL to use" "SECID195"
Thus, this example checks whether or not the IP addresses of the sender
domain's mail servers are on the Spamhaus black list.
-.new
The key that was used for a successful DNS list lookup is put into the variable
&$dnslist_matched$& (see section &<<SECID204>>&).
-.wen
.section "Variables set from DNS lists" "SECID204"
-.new
.cindex "expansion" "variables, set from DNS list"
.cindex "DNS list" "variables set from"
.vindex "&$dnslist_domain$&"
.endd
If this condition succeeds, the value in &$dnslist_matched$& might be
&`192.168.6.7`& (for example).
-.wen
If more than one address record is returned by the DNS lookup, all the IP
addresses are included in &$dnslist_value$&, separated by commas and spaces.
example, &$authenticated_id$& is only meaningful if the client has
authenticated, and you can check with the &%authenticated%& ACL condition.
-.new
If you want to limit the rate at which a recipient receives messages, you can
use the key &`$local_part@$domain`& with the &%per_rcpt%& option (see below) in
a RCPT ACL.
-.wen
Internally, Exim includes the smoothing constant &'p'& and the options in the
lookup key because they alter the meaning of the stored data. This is not true
still remember clients' past behaviour, but if you alter the other ratelimit
parameters Exim forgets past behaviour.
-.new
Each &%ratelimit%& condition can have up to three options. One option
specifies what Exim measures the rate of, and the second specifies how Exim
handles excessively fast clients. The third option can be &`noupdate`&, to
disable updating of the ratelimiting database (see section &<<rearatdat>>&).
The options are separated by a slash, like the other parameters. They may
appear in any order.
-.wen
.section "Ratelimit options for what is being measured" "ratoptmea"
The &%per_conn%& option limits the client's connection rate.
completely missing. You can follow the limit &'m'& in the configuration with K,
M, or G to specify limits in kilobytes, megabytes, or gigabytes, respectively.
+.new
The &%per_rcpt%& option causes Exim to limit the rate at which
recipients are accepted. To be effective, it would need to be used in
either the &%acl_smtp_rcpt%& or the &%acl_not_smtp%& ACL. In the
This command is essentially an alias of &%per_rcpt%& to make it clear
that the effect is to limit the rate at which individual commands,
rather than recipients, are accepted.
+.wen
.section "Ratelimit options for handling fast clients" "ratophanfas"
If a client's average rate is greater than the maximum, the rate limiting
hints, the callout cache, and ratelimit data).
-.new
.section "Reading ratelimit data without updating" "rearatdat"
.cindex "rate limitint" "reading data without updating"
If the &%noupdate%& option is present on a &%ratelimit%& ACL condition, Exim
In this example, the rate is tested and used to deny access (when it is too
high) in the connect ACL, but the actual computation of the remembered rate
happens later, on a per-command basis, in another ACL.
-.wen
.section "Available Exim variables" "SECID208"
-.new
.cindex "&[local_scan()]& function" "available Exim variables"
The header &_local_scan.h_& gives you access to a number of C variables. These
are the only ones that are guaranteed to be maintained from release to release.
Note, however, that you can obtain the value of any Exim expansion variable,
including &$recipients$&, by calling &'expand_string()'&. The exported
C variables are as follows:
-.wen
.vlist
.vitem &*int&~body_linecount*&
-.new
This variable contains the number of lines in the message's body.
.vitem &*int&~body_zerocount*&
This variable contains the number of binary zero bytes in the message's body.
-.wen
.vitem &*unsigned&~int&~debug_selector*&
This variable is set to zero when no debugging is taking place. Otherwise, it
git://git.exim.org / users / heiko / exim.git / commitdiff