. Update the Copyright year (only) when changing content.
. /////////////////////////////////////////////////////////////////////////////
-.set previousversion "4.96"
+.set previousversion "4.97"
.include ./local_params
.set ACL "access control lists (ACLs)"
.set drivernamemax "64"
.macro copyyear
-2022
+2023
.endmacro
. /////////////////////////////////////////////////////////////////////////////
way of representing the date and time of day).
.next
After the first hyphen, the next
-.new
eleven
-.wen
characters are the id of the process that received the message.
.next
-.new
There are two different possibilities for the final four characters:
.olist
.oindex "&%localhost_number%&"
500000 (250000) and added to
the fractional part of the time, which in this case is in units of 2 us (4 us).
.endlist
-.wen
.endlist
After a message has been received, Exim waits for the clock to tick at the
referenced from the configuration (for example, alias files) are changed,
because these are reread each time they are used.
-.new
Either a SIGTERM or a SIGINT signal should be used to cause the daemon
to cleanly shut down.
Subprocesses handling recceiving or delivering messages,
or for scanning the queue,
will not be affected by the termination of the daemon process.
-.wen
.cmdopt -bdf
This option has the same effect as &%-bd%& except that it never disconnects
Because macros in the config file are often used for secrets, those are only
available to admin users.
-.new
The word &"set"& at the start of a line, followed by a single space,
is recognised specially as defining a value for a variable.
The syntax is otherwise the same as the ACL modifier &"set ="&.
-.wen
.cmdopt -bem <&'filename'&>
.cindex "testing" "string expansion"
given.
Normally the daemon creates this socket, unless a &%-oX%& and &*no*& &%-oP%&
option is also present.
-.new
If this option is given then the socket will not be created. This is required
if the system is running multiple daemons, in which case it should
be used on all.
.next
obtaining a current queue size
.endlist
-.wen
.cmdopt -pd
.cindex "Perl" "starting the interpreter"
.cindex "multiple SMTP deliveries"
connection because of the hints that were set up during the first queue scan.
-.new
Two-phase queue runs should be used on systems which, even intermittently,
have a large queue (such as mailing-list operators).
They may also be useful for hosts that are connected to the Internet
intermittently.
-.wen
.vitem &%-q[q]i...%&
.oindex "&%-qi%&"
Such a daemon listens for incoming SMTP calls, and also starts a queue runner
process every 30 minutes.
-.new
.cindex "named queues" "queue runners"
It is possible to set up runners for multiple named queues within one daemon,
For example:
.code
exim -qGhipri/2m -q10m -qqGmailinglist/1h
.endd
-.wen
When a daemon is started by &%-q%& with a time value, but without &%-bd%&, no
pid file is written unless one is explicitly requested by the &%-oP%& option.
For the string-expansion kind of lookups, the query is given in the first
bracketed argument of the &${lookup ...}$& expansion.
-For the list-argument kind of lookup the quury is given by the remainder of the
+For the list-argument kind of lookup the query is given by the remainder of the
list item after the first semicolon.
.cindex "tainted data" "quoting for lookups"
-If tainted data is used in the query then it should be quuted by
+If tainted data is used in the query then it should be quoted by
using the &*${quote_*&<&'lookup-type'&>&*:*&<&'string'&>&*}*& expansion operator
appropriate for the lookup.
.endlist
[name="${quote_nisplus:$local_part}"]
.endd
.cindex "tainted data" "in lookups"
-.new
&*All*& tainted data used in a query-style lookup must be quoted
using a mechanism appropriate for the lookup type.
-.wen
See chapter &<<CHAPexpand>>& for full coverage of string expansions. The quote
operator can be used for all lookup types, but has no effect for single-key
lookups, since no quoting is ever needed in their key strings.
${lookup pgsql,servers=master/db/name/pw {UPDATE ...} }
.endd
-An older syntax places the servers specification before the query,
+.new
+A now-deprecated syntax places the servers specification before the query,
semicolon separated:
.code
${lookup mysql{servers=master; UPDATE ...} }
.endd
-The new version avoids potential issues with tainted
-arguments in the query, for explicit expansion.
+The new version avoids issues with tainted
+arguments explicitly expanded as part of the query.
+The entire string within the braces becomes tainted,
+including the server sepcification - which is not permissible.
+If the older sytax is used, a warning message will be logged.
+This syntax will be removed in a future release.
+.wen
+
&*Note*&: server specifications in list-style lookups are still problematic.
.oindex &%sqlite_dbfile%&
There are two ways of
specifying the file.
-The first is is by using the &%sqlite_dbfile%& main option.
+The first is by using the &%sqlite_dbfile%& main option.
The second, which allows separate files for each query,
is to use an option appended, comma-separated, to the &"sqlite"&
lookup type word. The option is the word &"file"&, then an equals,
.section "Expansion of lists" "SECTlistexpand"
.cindex "expansion" "of lists"
Each list is expanded as a single string before it is used.
+.cindex "tainted data" tracking
+&*Note*&: As a result, if any componend was tainted then the
+entire result string becomes tainted.
&'Exception: the router headers_remove option, where list-item
splitting is done before string-expansion.'&
below in section &<<SECTexpansionitems>>& onwards. Backslash is used as an
escape character, as described in the following section.
+.cindex "tainted data" tracking
+If any porttion of the result string is tainted, the entire result is.
+
Whether a string is expanded depends upon the context. Usually this is solely
dependent upon the option for which a value is sought; in this documentation,
options for which string expansion is performed are marked with † after
database lookups, and the use of expansion operators such as &%sg%&, &%substr%&
and &%nhash%&.
-.new
When reading lines from the standard input,
macros can be defined and ACL variables can be set.
For example:
set acl_m_myvar = bar
.endd
Such macros and variables can then be used in later input lines.
-.wen
Exim gives up its root privilege when it is called with the &%-be%& option, and
instead runs under the uid and gid it was called with, to prevent users from
add_header = :at_start:${authresults {$primary_hostname}}
.endd
This is safe even if no authentication results are available
-.new
and would generally be placed in the DATA ACL.
-.wen
.vitem "&*${certextract{*&<&'field'&>&*}{*&<&'certificate'&>&*}&&&
For each item
in this list, its value is placed in &$item$&, and then the condition is
evaluated.
-.new
Any modification of &$value$& by this evaluation is discarded.
-.wen
If the condition is true, &$item$& is added to the output as an
item in a new list; if the condition is false, the item is discarded. The
separator used for the output list is the same as the one used for the
This item inserts &"raw"& header lines. It is described with the &%header%&
expansion item in section &<<SECTexpansionitems>>& above.
-.vitem "&*${run<&'options'&> {*&<&'command&~arg&~list'&>&*}{*&<&'string1'&>&*}&&&
+.vitem "&*${run<&'options'&> {*&<&'command&~string'&>&*}{*&<&'string1'&>&*}&&&
{*&<&'string2'&>&*}}*&"
.cindex "expansion" "running a command"
.cindex "&%run%& expansion item"
and without whitespace.
If the option &'preexpand'& is not used,
-the command string is split into individual arguments by spaces
-and then each argument is expanded.
+the command string before expansion is split into individual arguments by spaces
+and then each argument is separately expanded.
Then the command is run
in a separate process, but under the same uid and gid. As in other command
executions from Exim, a shell is not used by default. If the command requires
a careful assessment for security vulnerabilities should be done.
If the option &'preexpand'& is used,
-the command and its arguments are first expanded as one string. The result is
-split apart into individual arguments by spaces, and then the command is run
-as above.
+the command string is first expanded as a whole.
+The expansion result is split apart into individual arguments by spaces,
+and then the command is run as above.
Since the arguments are split by spaces, when there is a variable expansion
which has an empty result, it will cause the situation that the argument will
simply be omitted when the program is actually executed by Exim. If the
-.new
.vitem &*${headerwrap_*&<&'cols'&>&*_*&<&'limit'&>&*:*&<&'string'&>&*}*&
.cindex header "wrapping operator"
.cindex expansion "header wrapping"
Whitespace at a chosen wrap point is removed.
A line-wrap consists of a newline followed by a tab,
and the tab is counted as 8 columns.
-.wen
rejections of MAIL and rejections of RCPT.
.tvar &$recipients$&
-.new
.tvar &$recipients_list$&
These variables both contain the envelope recipients for a message.
this variable is not intended for further processing.
The second is a proper Exim list; colon-separated.
-.wen
However, the variables
are not generally available, to prevent exposure of Bcc recipients in
.row &%dsn_advertise_hosts%& "advertise DSN extensions to these hosts"
.row &%ignore_fromline_hosts%& "allow &""From ""& from these hosts"
.row &%ignore_fromline_local%& "allow &""From ""& from local SMTP"
+.row &%limits_advertise_hosts%& "advertise LIMITS to these hosts"
.row &%pipelining_advertise_hosts%& "advertise pipelining to these hosts"
.row &%pipelining_connect_advertise_hosts%& "advertise pipelining to these hosts"
.row &%prdr_enable%& "advertise PRDR to all hosts"
See section &<<SECDKIMVFY>>&.
-.option dmarc_forensic_sender main string&!! unset
-.option dmarc_history_file main string unset
-.option dmarc_tld_file main string unset
+.option dmarc_forensic_sender main string&!! unset &&&
+ dmarc_history_file main string unset &&&
+ dmarc_tld_file main string unset
.cindex DMARC "main section options"
These options control DMARC processing.
See section &<<SECDMARC>>& for details.
dns_again_means_nonexist = *.in-addr.arpa
.endd
This option applies to all DNS lookups that Exim does,
-.new
except for TLSA lookups (where knowing about such failures
is security-relevant).
-.wen
It also applies when the
&[gethostbyname()]& or &[getipnodebyname()]& functions give temporary errors,
since these are most likely to be caused by DNS lookup problems. The
nowadays the ACL specified by &%acl_smtp_connect%& can also reject incoming
connections immediately.
-.new
If the connection is on a TLS-on-connect port then the TCP connection is
just dropped. Otherwise, an SMTP error is sent first.
-.wen
The ability to give an immediate rejection (either by this option or using an
ACL) is provided for use in unusual cases. Many hosts will just try again,
.code
hosts_connection_nolog = :
.endd
-.new
The hosts affected by this option also do not log "no MAIL in SMTP connection"
lines, as may commonly be produced by a monitoring system.
-.wen
.option hosts_require_alpn main "host list&!!" unset
+.new
+.option limits_advertise_hosts main "host list&!!" *
+.cindex LIMITS "suppressing advertising"
+.cindex "ESMTP extensions" LIMITS
+This option can be used to suppress the advertisement of the SMTP
+LIMITS extension (RFC 9422) to specific hosts.
+If permitted, Exim as a servier will advertise in the EHLO response
+the limit for RCPT commands set by the &%recipients_max%& option (if it is set)
+and the limit for MAIL commands set by the &%smtp_accept_max_per_connection%&
+option.
+,wen
+
.option local_from_check main boolean true
.cindex "&'Sender:'& header line" "disabling addition of"
.cindex "&'From:'& header line" "disabling checking of"
.option localhost_number main string&!! unset
.cindex "host" "locally unique number for"
.cindex "message ids" "with multiple hosts"
+.cindex multiple "systems sharing a spool"
+.cindex "multiple hosts" "sharing a spool"
+.cindex "shared spool directory"
+.cindex "spool directory" sharing
.vindex "&$localhost_number$&"
Exim's message ids are normally unique only within the local host. If
-uniqueness among a set of hosts is required, each host must set a different
+uniqueness among a set of hosts is required
+(eg. because they share a spool directory),
+each host must set a different
value for the &%localhost_number%& option. The string is expanded immediately
after reading the configuration file (so that a number can be computed from the
host name, for example) and the result of the expansion must be a number in the
range 0&--16 (or 0&--10 on operating systems with case-insensitive file
systems). This is available in subsequent string expansions via the variable
-&$localhost_number$&. When &%localhost_number is set%&, the final two
+&$localhost_number$&. When &%localhost_number%& is set, the final four
characters of the message id, instead of just being a fractional part of the
time, are computed from the time and the local host number as described in
section &<<SECTmessiden>>&.
The option is available only if Exim has been built with Oracle support.
-.new
.option panic_coredump main boolean false
This option is rarely needed but can help for some debugging investigations.
If set, when an internal error is detected by Exim which is sufficient
Note that most systems require additional administrative configuration
to permit write a core file for a setuid program, which is Exim's
common installed configuration.
-.wen
.option percent_hack_domains main "domain list&!!" unset
.cindex "&""percent hack""&"
option was not set.
-.option recipients_max main integer 50000
+.option recipients_max main integer&!! 50000
.cindex "limit" "number of recipients"
.cindex "recipient" "maximum number"
-If this option is set greater than zero, it specifies the maximum number of
+If the value resulting from expanding this option
+is set greater than zero, it specifies the maximum number of
original recipients for any message. Additional recipients that are generated
by aliasing or forwarding do not count. SMTP messages get a 452 response for
all recipients over the limit; earlier recipients are delivered as normal.
Non-SMTP messages with too many recipients are failed, and no deliveries are
done.
+.new
+For SMTP message the expansion is done after the connection is
+accepted (but before any SMTP conversation) and may depend on
+the IP addresses and port numbers of the connection.
+&*Note*&: If an expansion is used for the option,
+care should be taken that a resonable value results for
+non-SMTP messages.
+.wen
+
.cindex "RCPT" "maximum number of incoming"
&*Note*&: The RFCs specify that an SMTP server should accept at least 100
RCPT commands in a single message.
smtp_banner = $smtp_active_hostname ESMTP Exim \
$version_number $tod_full
.endd
-.new
Failure to expand the string causes a panic error;
a forced fail just closes the connection.
-.wen
If you want to create a
multiline response to the initial SMTP connection, use &"\n"& in the string at
appropriate points, but not at the end. Note that the 220 code is not included
&%tls_require_ciphers%& option).
After expansion it must contain
-.new
one or (only for OpenSSL versiona 1.1.1 onwards) more
-.wen
EC curve names, such as &`prime256v1`&, &`secp384r1`&, or &`P-521`&.
Consult your OpenSSL manual for valid curve names.
&`auto`& selects &`prime256v1`&. For more recent OpenSSL versions
&`auto`& tells the library to choose.
-.new
If the option expands to an empty string, the effect is undefined.
-.wen
.option tls_ocsp_file main string&!! unset
When the message is about to be written out, the command specified by
&%transport_filter%& is started up in a separate, parallel process, and
the entire message, including the header lines, is passed to it on its standard
-input (this in fact is done from a third process, to avoid deadlock). The
-command must be specified as an absolute path.
+input (this in fact is done from a third process, to avoid deadlock).
+The command must be specified as an absolute path.
+
+The process run by the command must use its standard input as the message
+data to be transformed, and write the results on its standard output.
The lines of the message that are written to the transport filter are
terminated by newline (&"\n"&). The message is passed to the filter before any
No part of the resulting command may be tainted.
-.option environment pipe string&!! unset
+.option environment pipe "string list&!!" unset
.cindex "&(pipe)& transport" "environment for command"
.cindex "environment" "&(pipe)& transport"
This option is used to add additional variables to the environment in which the
For testing purposes, this value can be overridden by the &%-oB%& command line
option.
+.new
+.cindex "ESMTP extensions" LIMITS
+If the peer advertises a LIMITS extension with a MAILMAX value,
+and either TLSS is in use or was not advertised,
+that value also constrains the result of this option.
+.wen
+
.option dane_require_tls_ciphers smtp string&!! unset
.cindex "TLS" "requiring specific ciphers for DANE"
Exim can pull out a server name, if there is one, from the response to the
client's SMTP EHLO command.
-The default value of this option:
+For normal STARTTLS use, the default value of this option:
.code
${if and { {match {$host} {.outlook.com\$}} \
{match {$item} {\N^250-([\w.]+)\s\N}} \
} {$1}}
.endd
suffices for one known case.
+
During the expansion of this option the &$item$& variable will have the
server's EHLO response.
+
+.new
+For TLS-on-connect connections we do not have an EHLO
+response to use. Because of this the default value of this option is
+set to a static string for those cases, meaning that resumption will
+always be attempted if permitted by the &%tls_resumption_hosts%& option.
+.wen
+
The result of the option expansion is included in the key used to store and
retrieve the TLS session, for session resumption.
TLS session for any host that matches this list.
&%tls_verify_certificates%& should also be set for the transport.
-.new
The default is &"**"& if DANE is not in use for the connection,
or if DANE-TA us used.
It is empty if DANE-EE is used.
-.wen
.option hosts_require_alpn smtp "host list&!!" unset
.cindex ALPN "require negotiation in client"
.option max_rcpt smtp integer&!! 100
.cindex "RCPT" "maximum number of outgoing"
This option,
-.new
after expansion,
-.wen
limits the number of RCPT commands that are sent in a single
SMTP message transaction.
A value setting of zero disables the limit.
-.new
If a constant is given,
-.wen
each set of addresses is treated independently, and
so can cause parallel connections to the same host if &%remote_max_parallel%&
permits this.
+.new
+.cindex "ESMTP extensions" LIMITS
+If the peer advertises a LIMITS extension with a RCPTMAX value,
+and either TLSS is in use or was not advertised,
+that value also constrains the result of this option
+and no parallel connections will be caused on meeting the RCPTMAX limit.
+.wen
+
.option message_linelength_limit smtp integer 998
.cindex "line length" limit
This option sets the maximum line length, in bytes, that the transport
will send. Any messages with lines exceeding the given value
+(before a transport filter, if any)
will fail and a failure-DSN ("bounce") message will if possible be returned
to the sender.
The default value is that defined by the SMTP standards.
only messages having the domain used for the DANE TLSA lookup are
sent on the connection.
+.new
+.cindex "ESMTP extensions" LIMITS
+If the peer advertises a LIMITS extension with a RCPTDOMAINMAX value,
+and either TLSS is in use or was not advertised,
+this option is regarded as being false.
+.wen
+
+
.option port smtp string&!! "see below"
.cindex "port" "sending TCP/IP"
.cindex "TCP/IP" "setting outgoing port"
Successful authentication sets up information used by the
&%authresults%& expansion item.
-.new
.cindex authentication "failure event, server"
If an authenticator is run and does not succeed,
an event (see &<<CHAPevents>>&) of type "auth:fail" is raised.
If the event is serviced and a string is returned then the string will be logged
instead of the default log line.
See <<CHAPevents>> for details on events.
-.wen
.section "Testing server authentication" "SECID169"
try again later. If there are any backup hosts available, they are tried in the
usual way.
-.new
.next
.cindex authentication "failure event, client"
If the response to authentication is a permanent error (5&'xx'& code),
will be valid.
If the event is serviced and a string is returned then the string will be logged.
See <<CHAPevents>> for details on events.
-.wen
.next
If the response to authentication is a permanent error (5&'xx'& code), Exim
server_set_id = $auth1
.endd
-.new
&*Note*&: plaintext authentication methods such as PLAIN and LOGIN
should not be advertised on cleartext SMTP connections.
See the discussion in section &<<SECTplain_TLS>>&.
-.wen
If the SMTP connection is encrypted, or if &$sender_host_address$& is equal to
&$received_ip_address$& (that is, the connection is local), the &"secured"&
(If an API is found to let OpenSSL be configured in this way,
let the Exim Maintainers know and we'll likely use it).
.next
-With GnuTLS, if an explicit list is used for the &%tls_privatekey%& main option
-main option, it must be ordered to match the &%tls_certificate%& list.
+With GnuTLS, if an explicit list is used for the &%tls_privatekey%& main option,
+it must be ordered to match the &%tls_certificate%& list.
.next
Some other recently added features may only be available in one or the other.
This should be documented with the feature. If the documentation does not
.next
Add TLSA DNS records. These say what the server certificate for a TLS connection should be.
.next
-Offer a server certificate, or certificate chain, in TLS connections which is is anchored by one of the TLSA records.
+Offer a server certificate, or certificate chain, in TLS connections which is anchored by one of the TLSA records.
.endlist
There are no changes to Exim specific to server-side operation of DANE.
the message override the banner message that is otherwise specified by the
&%smtp_banner%& option.
-.new
For tls-on-connect connections, the ACL is run before the TLS connection
is accepted; if the ACL does not accept then the TCP connection is dropped without
any TLS startup attempt and without any SMTP response being transmitted.
-.wen
.subsection "The EHLO/HELO ACL" SECID192
More than one header can be removed at the same time by using a colon separated
list of header specifiers.
-.new
If a specifier does not start with a circumflex (^)
then it is treated as a header name.
The header name matching is case insensitive.
.code
remove_header = \N^(?i)Authentication-Results\s*::\s*example.org;\N
.endd
-.wen
List expansion is not performed, so you cannot use hostlists to
create a list of headers, however both connection and message variable expansion
(the -D file). The file is open for reading and writing, but updating it is not
recommended. &*Warning*&: You must &'not'& close this file descriptor.
-The descriptor is positioned at character 19 of the file, which is the first
-character of the body itself, because the first 19 characters are the message
-id followed by &`-D`& and a newline. If you rewind the file, you should use the
+The descriptor is positioned at character 26 of the file, which is the first
+character of the body itself, because the first 26 characters (19 characters
+before Exim 4.97) are the message id followed by &`-D`& and a newline.
+If you rewind the file, you should use the
macro SPOOL_DATA_START_OFFSET to reset to the start of the data, just in
case this changes in some future version.
.next
follows:
.ilist
-LF not preceded by CR is treated as a line ending.
-.next
CR is treated as a line ending; if it is immediately followed by LF, the LF
is ignored.
.next
.next
If the first header line received in a message ends with CRLF, a subsequent
bare LF in a header line is treated in the same way as a bare CR in a header
-line.
+line and a bare LF in a body line is replaced with a space.
+.next
+If the first header line received in a message does not end with CRLF, a subsequent
+LF not preceded by CR is treated as a line ending.
.endlist
.irow &`deliver_time`& "time taken to attempt delivery"
.irow &`delivery_size`& "add &`S=`&&'nnn'& to => lines"
.irow &`dkim`& * "DKIM verified domain on <= lines"
-.irow &`dkim_verbose`& "separate full DKIM verification result line, per signature"
+.irow &`dkim_verbose`& "separate full DKIM verification result line, per signature; DKIM signing"
.irow &`dnslist_defer`& * "defers of DNS list (aka RBL) lookups"
.irow &`dnssec`& "DNSSEC secured lookups"
.irow &`etrn`& * "ETRN commands"
.irow &`tls_peerdn`& "TLS peer DN on <= and => lines"
.irow &`tls_resumption`& "append * to cipher field"
.irow &`tls_sni`& "TLS SNI on <= lines"
-.irow &`unknown_in_list`& "DNS lookup failed in list match"
+.irow &`unknown_in_list`& "lookup failed in list match"
.irow &`all`& "&*all of the above*&"
.endtable
See also the &%slow_lookup_log%& main configuration option,
between the caller and Exim.
.next
.cindex "log" "connection identifier"
-.new
&%connection_identifier%&: An identifier for the accepted connection is added to
connection start and end lines and to message accept lines.
The identifier is tagged by Ci=.
The value is PID-based, so will reset on reboot and will wrap.
-.wen
.next
.cindex "log" "connection rejections"
&%connection_reject%&: A log entry is written whenever an incoming SMTP
.cindex log "DKIM verification"
.cindex DKIM "verification logging"
&%dkim_verbose%&: A log entry is written for each attempted DKIM verification.
+.new
+Also, on message delivery lines signing information (domain and selector)
+is added, tagged with DKIM=.
+.wen
.next
.cindex "log" "dnslist defer"
.cindex "DNS list" "logging defer"
.next
.cindex "log" "DNS failure in list"
&%unknown_in_list%&: This setting causes a log entry to be written when the
-result of a list match is failure because a DNS lookup failed.
+result of a list match is failure because a DNS lookup failed, or because
+a bad IP address was in the list.
.endlist
.option dkim_sign_headers smtp string&!! "see below"
If set, this option must expand to a colon-separated
list of header names.
-Headers with these names, or the absence or such a header, will be included
+Headers with these names, or the absence of such a header, will be included
in the message signature.
When unspecified, the header names listed in RFC4871 will be used,
whether or not each header is present in the message.
.option dkim_timestamps smtp integer&!! unset
This option controls the inclusion of timestamp information in the signature.
If not set, no such information will be included.
-Otherwise, must be an unsigned number giving an offset in seconds from the current time
-for the expiry tag
-(eg. 1209600 for two weeks);
-both creation (t=) and expiry (x=) tags will be included.
+.new
+Otherwise, must be an unsigned number giving an offset in seconds from the
+current time for the expiry tag (e.g. 1209600 for two weeks); both creation
+(t=) and expiry (x=) tags will be included unless the offset is 0 (no expiry).
+.wen
RFC 6376 lists these tags as RECOMMENDED.
.subsection "SRS (Sender Rewriting Scheme)" SECTSRS
.cindex SRS "sender rewriting scheme"
+.cindex VERP "variable envelope return path"
SRS can be used to modify sender addresses when forwarding so that
SPF verification does not object to them.
-It operates by encoding the original envelope sender in a new
+It can also be used to identify a received bounce message as
+likely (or not) having been trigged by a message from the
+local system, and for identifying dead addresses in mailing lists.
+It is one implementation of a VERP (Variable Envelope Return Path) method.
+
+SRS operates by encoding the original envelope sender in a new
sender local part and using a domain run by the forwarding site
as the new domain for the sender. Any DSN message should be returned
to this new sender at the forwarding site, which can extract the
If it is, the condition will return true and the variable
&$srs_recipient$& will be set to the decoded (original) value.
-.new
If the second argument is empty then the condition returns true if
the first argument is in valid SRS formet, else false.
The variable &$srs_recipient$& is not set for this case.
-.wen
.endlist
Example usage:
no other use is made of it.
For a tcp:connect event, if the connection is being made to a proxy
-then the address and port variables will be that of the proxy and not
-the target system.
+then the &$host_address$& and &$host_port$& variables
+will be that of the proxy and not the target system.
For tls:cert events, if GnuTLS is in use this will trigger only per
chain element received on the connection.
git://git.exim.org / exim.git / blobdiff