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The first part of the run time configuration file contains three types of item:
-bP
command line option displays its value to admin users
only. See section Common option syntax for a description of the syntax of these option
settings.
This chapter specifies all the main configuration options, along with their types and default values. For ease of finding a particular option, they appear in alphabetical order in section Alphabetical list of main options below. However, because there are now so many options, they are first listed briefly in functional groups, as an aid to finding the name of the option you are looking for. Some options are listed in more than one group.
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| to run for |
| do no IPv6 processing |
| for broken files - should not happen |
| for unique message ids in clusters |
| how much to show in |
| run in "MUA wrapper" mode |
| top-bit characters are printing |
| force time zone |
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| override compiled-in value |
| override compiled-in value |
| override compiled-in value |
| default from |
| use multiple directories |
| override compiled-in value |
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| groups that are Exim admin users |
| drop root for delivery processes |
| insert Sender: if necessary |
| for testing From: for local sender |
| for testing From: for local sender |
| keep Sender: from untrusted user |
| do not run deliveries as these |
| forced delivery requires admin user |
| queue listing requires admin user |
| groups that are trusted |
| users that are trusted |
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| exemption from connect logging |
| override compiled-in value |
| set/unset optional logging |
| add timezone to log lines |
| create per-message logs |
| after message completion |
| for SIGUSR1 and exiwhat |
| controls duplicate log lines on syslog |
| set syslog "facility" field |
| set syslog "ident" field |
| timestamp syslog lines |
| control use of message log |
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| sets time for retrying frozen messages |
| send message when freezing |
| to another directory |
| keep frozen messages only so long |
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| used if no server in query |
| set protocol version |
| lookup files held open |
| as it says |
| as it says |
| as it says |
| as it says |
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| used to build Message-ID: header |
| ditto |
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| always start the interpreter |
| code to obey when starting Perl |
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| default ports |
| number of times to retry |
| time to sleep between tries |
| not necessarily listened on |
| on which to listen, with optional ports |
| override compiled-in value |
| maximum simultaneous queue runners |
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| before accepting a message |
| before accepting a message |
| before accepting a message |
| before accepting a message |
| no queue deliveries if load high |
| queue incoming if load high |
| maximum simultaneous queue runners |
| parallel SMTP delivery per message |
| simultaneous incoming connections |
| non-mail commands |
| hosts to which the limit applies |
| messages per connection |
| connections from one host |
| queue mail if more connections |
| queue if more messages per connection |
| only reserve hosts if more connections |
| from SIZE on MAIL command |
| passed to TCP/IP stack |
| SMTP from reserved hosts if load high |
| these are the reserve hosts |
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| ACL for non-SMTP messages |
| ACL for non-SMTP MIME parts |
| ACL for start of non-SMTP message |
| ACL for AUTH |
| ACL for connection |
| ACL for DATA |
| ACL for ETRN |
| ACL for EXPN |
| ACL for EHLO or HELO |
| ACL for MAIL |
| ACL for AUTH on MAIL command |
| ACL for MIME parts |
| ACL for start of data |
| ACL for QUIT |
| ACL for RCPT |
| ACL for STARTTLS |
| ACL for VRFY |
| specify virus scanner |
| check length of RFC 2047 "encoded words" |
| control CSA parent search depth |
| en/disable CSA IP reverse search |
| total size of message header |
| individual header line limit |
| allow syntactic junk from these hosts |
| allow illegal chars in HELO names |
| lookup hostname for these HELO names |
| HELO soft-checked for these hosts |
| HELO hard-checked for these hosts |
| host name looked up for these hosts |
| order of DNS and local name lookups |
| reject connection from these hosts |
| useful in some cluster configurations |
| timeout for |
| for all messages |
| recognize %-hack for these domains |
| set interface to SpamAssassin |
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| timeout for negative domain cache item |
| timeout for positive domain cache item |
| timeout for negative address cache item |
| timeout for positive address cache item |
| string to use for "random" testing |
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| advertise TLS to these hosts |
| location of server certificate |
| certificate revocation list |
| DH parameters for server |
| specify SSMTP (SMTPS) ports |
| location of server private key |
| don't reset after starting TLS |
| specify acceptable cipers |
| try to verify client certificate |
| expected client certificates |
| insist on client certificate verify |
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| useful in NIS environments |
| used when creating Sender: |
| ditto |
| for systems that truncate |
| used when no login name found |
| ditto |
| for recognizing "From " lines |
| ditto |
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| total size of message header |
| individual header line limit |
| applies to all messages |
| recognize %-hack for these domains |
| expanded to make Received: |
| for mail loop detection |
| limit per message |
| permanently reject excess |
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| for non-SMTP messages |
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See also the Policy controls section above.
| host name looked up for these hosts |
| order of DNS and local name lookups |
| may send unqualified recipients |
| make ident calls to these hosts |
| zero disables ident calls |
| may send unqualified senders |
| some TCP/IP magic |
| simultaneous incoming connections |
| non-mail commands |
| hosts to which the limit applies |
| messages per connection |
| connections from one host |
| queue mail if more connections |
| queue if more messages per connection |
| only reserve hosts if more connections |
| host name to use in messages |
| text for welcome banner |
| from SIZE on MAIL command |
| passed to TCP/IP stack |
| of SMTP command/responses |
| what to run for ETRN |
| only one at once |
| only reserve hosts if this load |
| before dropping connection |
| apply ratelimiting to these hosts |
| ratelimit for MAIL commands |
| ratelimit for RCPT commands |
| per command or data line |
| these are the reserve hosts |
| give detail on rejections |
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| advertise 8BITMIME |
| advertise AUTH to these hosts |
| allow "From " from these hosts |
| allow "From " from local SMTP |
| advertise pipelining to these hosts |
| advertise TLS to these hosts |
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| recognize domain literal syntax |
| allow MX to point to IP address |
| in addresses |
| check length of RFC 2047 "encoded words" |
| from incoming messages |
| from incoming messages |
| affects |
| default for translations |
| default for senders |
| default for recipients |
| from incoming messages |
| in addresses |
| at end of addresses |
| untrusted can set envelope sender |
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| locate system filter |
| transport for delivery to a directory |
| transport for delivery to a file |
| group for filter running |
| transport for delivery to a pipe |
| transport for autoreply delivery |
| user for filter running |
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| do no IPv6 processing |
| for broken domains |
| pre-DNS syntax check |
| only v4 lookup for these domains |
| parameter for resolver |
| parameter for resolver |
| hold delivery for these domains |
| for routing checks |
| no immediate delivery for these |
| no immediate delivery at all |
| no immediate delivery if file exists |
| no immediate delivery if load is high |
| allow command line to override |
| order of arrival |
| of simultaneous queue runners |
| no immediate SMTP delivery for these |
| parallel SMTP delivery per message |
| order of remote deliveries |
| timeout for retry data |
| safety net for retry rules |
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| content of bounce |
| content of bounce |
| include body if returning message |
| include original message in bounce |
| limit on returned message |
| send authenticated sender with bounce |
| copy bounce messages |
| Reply-to: in bounces |
| time schedule |
| condition for warning messages |
| discard undeliverable bounces |
| give detail on rejections |
| content of warning message |
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Those options that undergo string expansion before use are marked with *.
| Use: main | Type: boolean | Default: false |
This option causes Exim to send 8BITMIME in its response to an SMTP EHLO command, and to accept the BODY= parameter on MAIL commands. However, though Exim is 8-bit clean, it is not a protocol converter, and it takes no steps to do anything special with messages received by this route. Consequently, this option is turned off by default.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when a non-SMTP message has been read and is on the point of being accepted. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run for individual MIME parts of non-SMTP
messages. It operates in exactly the same way as acl_smtp_mime
operates for
SMTP messages.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run before Exim starts reading a non-SMTP message. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when an SMTP AUTH command is received. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when an SMTP connection is received. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run after an SMTP DATA command has been processed and the message itself has been received, but before the final acknowledgement is sent. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when an SMTP ETRN command is received. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when an SMTP EXPN command is received. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when an SMTP EHLO or HELO command is received. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when an SMTP MAIL command is received. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when there is an AUTH parameter on a MAIL command. See chapter Access control lists for details of ACLs, and chapter SMTP authentication for details of authentication.
| Use: main | Type: string* | Default: unset |
This option is available when Exim is built with the content-scanning extension. It defines the ACL that is run for each MIME part in a message. See section Scanning MIME parts for details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when an SMTP DATA command is received, before the message itself is received. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when an SMTP QUIT command is received. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when an SMTP RCPT command is received. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when an SMTP STARTTLS command is received. See chapter Access control lists for further details.
| Use: main | Type: string* | Default: unset |
This option defines the ACL that is run when an SMTP VRFY command is received. See chapter Access control lists for further details.
| Use: main | Type: string list* | Default: unset |
This option is expanded just once, at the start of Exim's processing. If the
current group or any of the supplementary groups of an Exim caller is in this
colon-separated list, the caller has admin privileges. If all your system
programmers are in a specific group, for example, you can give them all Exim
admin privileges by putting that group in admin_groups
. However, this does
not permit them to read Exim's spool files (whose group owner is the Exim gid).
To permit this, you have to add individuals to the Exim group.
| Use: main | Type: boolean | Default: false |
If this option is set, the RFC 2822 domain literal format is permitted in email addresses. The option is not set by default, because the domain literal format is not normally required these days, and few people know about it. It has, however, been exploited by mail abusers.
Unfortunately, it seems that some DNS black list maintainers are using this
format to report black listing to postmasters. If you want to accept messages
addressed to your hosts by IP address, you need to set
allow_domain_literals
true, and also to add `@[]' to the list of local
domains (defined in the named domain list local_domains
in the default
configuration). This "magic string" matches the domain literal form of all
the local host's IP addresses.
| Use: main | Type: boolean | Default: false |
It appears that more and more DNS zone administrators are breaking the rules
and putting domain names that look like IP addresses on the right hand side of
MX records. Exim follows the rules and rejects this, giving an error message
that explains the mis-configuration. However, some other MTAs support this
practice, so to avoid "Why can't Exim do this?" complaints,
allow_mx_to_ip
exists, in order to enable this heinous activity. It is not
recommended, except when you have no other choice.
| Use: main | Type: boolean | Default: false |
Lots of discussion is going on about internationalized domain names. One camp is strongly in favour of just using UTF-8 characters, and it seems that at least two other MTAs permit this. This option allows Exim users to experiment if they wish.
If it is set true, Exim's domain parsing function allows valid
UTF-8 multicharacters to appear in domain name components, in addition to
letters, digits, and hyphens. However, just setting this option is not
enough; if you want to look up these domain names in the DNS, you must also
adjust the value of dns_check_names_pattern
to match the extended form. A
suitable setting is:
dns_check_names_pattern = (?i)^(?>(?(1)\.|())[a-z0-9\xc0-\xff]\ (?>[-a-z0-9\x80-\xff]*[a-z0-9\x80-\xbf])?)+$ |
Alternatively, you can just disable this feature by setting
dns_check_names_pattern = |
That is, set the option to an empty string so that no check is done.
| Use: main | Type: host list* | Default: * |
If any server authentication mechanisms are configured, Exim advertises them in
response to an EHLO command only if the calling host matches this list.
Otherwise, Exim does not advertise AUTH.
Exim does not accept AUTH commands from clients to which it has not
advertised the availability of AUTH. The advertising of individual
authentication mechanisms can be controlled by the use of the
server_advertise_condition
generic authenticator option on the individual
authenticators. See chapter SMTP authentication for further details.
Certain mail clients (for example, Netscape) require the user to provide a name
and password for authentication if AUTH is advertised, even though it may
not be needed (the host may accept messages from hosts on its local LAN without
authentication, for example). The auth_advertise_hosts
option can be used
to make these clients more friendly by excluding them from the set of hosts to
which Exim advertises AUTH.
If you want to advertise the availability of AUTH only when the connection is encrypted using TLS, you can make use of the fact that the value of this option is expanded, with a setting like this:
auth_advertise_hosts = ${if eq{$tls_cipher}{}{}{*}} |
If $tls_cipher
is empty, the session is not encrypted, and the result of
the expansion is empty, thus matching no hosts. Otherwise, the result of the
expansion is *, which matches all hosts.
| Use: main | Type: time | Default: 0s |
If this option is set to a time greater than zero, a queue runner will try a new delivery attempt on any frozen message, other than a bounce message, if this much time has passed since it was frozen. This may result in the message being re-frozen if nothing has changed since the last attempt. It is a way of saying "keep on trying, even though there are big problems".
Note: This is an old option, which predates timeout_frozen_after
and
ignore_bounce_errors_after
. It is retained for compatibility, but it is not
thought to be very useful any more, and its use should probably be avoided.
| Use: main | Type: string | Default: see below |
This option is available if Exim is built with the content-scanning extension. It specifies which anti-virus scanner to use. The default value is:
sophie:/var/run/sophie |
If the value of av_scanner
starts with dollar character, it is expanded
before use. See section Scanning for viruses for further details.
| Use: main | Type: string | Default: unset |
This option supplies the name of a command that is run when Exim is called with
the -bi
option (see chapter The Exim command line). The string value is
just the command name, it is not a complete command line. If an argument is
required, it must come from the -oA
command line option.
| Use: main | Type: string | Default: unset |
This option defines a template file containing paragraphs of text to be used
for constructing bounce messages. Details of the file's contents are given in
chapter Customizing bounce and warning messages. See also warn_message_file
.
| Use: main | Type: string | Default: unset |
When this option is set, its contents are included in the default bounce
message immediately after "This message was created automatically by mail
delivery software." It is not used if bounce_message_file
is set.
| Use: main | Type: boolean | Default: true |
This option controls whether the body of an incoming message is included in a
bounce message when bounce_return_message
is true. The default setting
causes the entire message, both header and body, to be returned (subject to the
value of bounce_return_size_limit
). If this option is false, only the
message header is included. In the case of a non-SMTP message containing an
error that is detected during reception, only those header lines preceding the
point at which the error was detected are returned.
| Use: main | Type: boolean | Default: true |
If this option is set false, none of the original message is included in
bounce messages generated by Exim. See also bounce_return_size_limit
and
bounce_return_body
.
| Use: main | Type: integer | Default: 100K |
This option sets a limit in bytes on the size of messages that are returned to
senders as part of bounce messages when bounce_return_message
is true. The
limit should be less than the value of the global message_size_limit
and of
any message_size_limit
settings on transports, to allow for the bounce text
that Exim generates. If this option is set to zero there is no limit.
When the body of any message that is to be included in a bounce message is greater than the limit, it is truncated, and a comment pointing this out is added at the top. The actual cutoff may be greater than the value given, owing to the use of buffering for transferring the message in chunks (typically 8K in size). The idea is to save bandwidth on those undeliverable 15-megabyte messages.
| Use: main | Type: string | Default: unset |
This option provides an authenticated sender address that is sent with any bounce messages generated by Exim that are sent over an authenticated SMTP connection. A typical setting might be:
bounce_sender_authentication = mailer-daemon@my.domain.example |
which would cause bounce messages to be sent using the SMTP command:
MAIL FROM:<> AUTH=mailer-daemon@my.domain.example |
The value of bounce_sender_authentication
must always be a complete email
address.
| Use: main | Type: time | Default: 3h |
This option specifies the expiry time for negative callout cache data for a domain. See section Callout verification for details of callout verification, and section Callout caching for details of the caching.
| Use: main | Type: time | Default: 7d |
This option specifies the expiry time for positive callout cache data for a domain. See section Callout verification for details of callout verification, and section Callout caching for details of the caching.
| Use: main | Type: time | Default: 2h |
This option specifies the expiry time for negative callout cache data for an address. See section Callout verification for details of callout verification, and section Callout caching for details of the caching.
| Use: main | Type: time | Default: 24h |
This option specifies the expiry time for positive callout cache data for an address. See section Callout verification for details of callout verification, and section Callout caching for details of the caching.
| Use: main | Type: string* | Default: see below |
This option defines the "random" local part that can be used as part of callout verification. The default value is
$primary_host_name-$tod_epoch-testing |
See section Additional parameters for callouts for details of how this value is used.
| Use: main | Type: integer | Default: 0 |
See check_spool_space
below.
| Use: main | Type: integer | Default: 0 |
See check_spool_space
below.
| Use: User: main | Type: boolean | Default: true |
RFC 2047 defines a way of encoding non-ASCII characters in headers using a
system of "encoded words". The RFC specifies a maximum length for an encoded
word; strings to be encoded that exceed this length are supposed to use
multiple encoded words. By default, Exim does not recognize encoded words that
exceed the maximum length. However, it seems that some software, in violation
of the RFC, generates overlong encoded words. If check_rfc2047_length
is
set false, Exim recognizes encoded words of any length.
| Use: main | Type: integer | Default: 0 |
See check_spool_space
below.
| Use: main | Type: integer | Default: 0 |
The four check_...
options allow for checking of disk resources before a
message is accepted.
When any of these options are set, they apply to all incoming messages. If you
want to apply different checks to different kinds of message, you can do so by
testing the the variables $log_inodes
, $log_space
, $spool_inodes
, and
$spool_space
in an ACL with appropriate additional conditions.
check_spool_space
and check_spool_inodes
check the spool partition if
either value is greater than zero, for example:
check_spool_space = 10M check_spool_inodes = 100 |
The spool partition is the one that contains the directory defined by SPOOL_DIRECTORY in `Local/Makefile'. It is used for holding messages in transit.
check_log_space
and check_log_inodes
check the partition in which log
files are written if either is greater than zero. These should be set only if
log_file_path
and spool_directory
refer to different partitions.
If there is less space or fewer inodes than requested, Exim refuses to accept
incoming mail. In the case of SMTP input this is done by giving a 452 temporary
error response to the MAIL command. If ESMTP is in use and there was a
SIZE parameter on the MAIL command, its value is added to the
check_spool_space
value, and the check is performed even if
check_spool_space
is zero, unless no_smtp_check_spool_space
is set.
The values for check_spool_space
and check_log_space
are held as a
number of kilobytes. If a non-multiple of 1024 is specified, it is rounded up.
For non-SMTP input and for batched SMTP input, the test is done at start-up; on failure a message is written to stderr and Exim exits with a non-zero code, as it obviously cannot send an error message of any kind.
| Use: main | Type: string | Default: `smtp' |
This option specifies one or more default SMTP ports on which the Exim daemon
listens. See chapter Starting the daemon and the use of network interfaces for details of how it is used. For
backward compatibility, daemon_smtp_port
(singular) is a synonym.
| Use: main | Type: integer | Default: 9 |
This option, along with daemon_startup_sleep
, controls the retrying done by
the daemon at startup when it cannot immediately bind a listening socket
(typically because the socket is already in use): daemon_startup_retries
defines the number of retries after the first failure, and
daemon_startup_sleep
defines the length of time to wait between retries.
| Use: main | Type: time | Default: 30s |
See daemon_startup_retries
.
| Use: main | Type: time list | Default: 24h |
When a message is delayed, Exim sends a warning message to the sender at intervals specified by this option. The data is a colon-separated list of times after which to send warning messages. If the value of the option is an empty string or a zero time, no warnings are sent. Up to 10 times may be given. If a message has been on the queue for longer than the last time, the last interval between the times is used to compute subsequent warning times. For example, with
delay_warning = 4h:8h:24h |
the first message is sent after 4 hours, the second after 8 hours, and the third one after 24 hours. After that, messages are sent every 16 hours, because that is the interval between the last two times on the list. If you set just one time, it specifies the repeat interval. For example, with:
delay_warning = 6h |
messages are repeated every six hours. To stop warnings after a given time, set a very large time at the end of the list. For example:
delay_warning = 2h:12h:99d |
| Use: main | Type: string* | Default: see below |
The string is expanded at the time a warning message might be sent. If all the
deferred addresses have the same domain, it is set in $domain
during the
expansion. Otherwise $domain
is empty. If the result of the expansion is a
forced failure, an empty string, or a string matching any of "0", "no" or
"false" (the comparison being done caselessly) then the warning message is
not sent. The default is:
delay_warning_condition = ${if or {\ { !eq{$h_list-id:$h_list-post:$h_list-subscribe:}{} }\ { match{$h_precedence:}{(?i)bulk|list|junk} }\ { match{$h_auto-submitted:}{(?i)auto-generated|auto-replied} }\ } {no}{yes}} |
This suppresses the sending of warnings for messages that contain List-ID:, List-Post:, or List-Subscribe: headers, or have "bulk", "list" or "junk" in a Precedence: header, or have "auto-generated" or "auto-replied" in an Auto-Submitted: header.
| Use: main | Type: boolean | Default: false |
If this option is set true, Exim drops its root privilege at the start of a delivery process, and runs as the Exim user throughout. This severely restricts the kinds of local delivery that are possible, but is viable in certain types of configuration. There is a discussion about the use of root privilege in chapter Security considerations.
| Use: main | Type: fixed-point | Default: unset |
When this option is set, a queue run is abandoned if the system load average
becomes greater than the value of the option. The option has no effect on
ancient operating systems on which Exim cannot determine the load average.
See also queue_only_load
and smtp_load_reserve
.
| Use: main | Type: boolean | Default: true |
Exim's transports have an option for adding a Delivery-date: header to a message when it is delivered, in exactly the same way as Return-path: is handled. Delivery-date: records the actual time of delivery. Such headers should not be present in incoming messages, and this option causes them to be removed at the time the message is received, to avoid any problems that might occur when a delivered message is subsequently sent on to some other recipient.
| Use: main | Type: boolean | Default: false |
If this option is set true, even if the Exim binary has IPv6 support, no IPv6
activities take place. AAAA records are never looked up, and any IPv6 addresses
that are listed in local_interfaces
, data for the manualroute
router,
etc. are ignored. If IP literals are enabled, the ipliteral
router declines
to handle IPv6 literal addresses.
| Use: main | Type: domain list* | Default: unset |
DNS lookups give a "try again" response for the DNS errors
"non-authoritative host not found" and "SERVERFAIL". This can cause Exim to
keep trying to deliver a message, or to give repeated temporary errors to
incoming mail. Sometimes the effect is caused by a badly set up name server and
may persist for a long time. If a domain which exhibits this problem matches
anything in dns_again_means_nonexist
, it is treated as if it did not exist.
This option should be used with care. You can make it apply to reverse lookups
by a setting such as this:
dns_again_means_nonexist = *.in-addr.arpa |
This option applies to all DNS lookups that Exim does. 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
dnslookup
router has some options of its own for controlling what happens
when lookups for MX or SRV records give temporary errors. These more specific
options are applied after this global option.
| Use: main | Type: string | Default: see below |
When this option is set to a non-empty string, it causes Exim to check domain names for characters that are not allowed in host names before handing them to the DNS resolver, because some resolvers give temporary errors for names that contain unusual characters. If a domain name contains any unwanted characters, a "not found" result is forced, and the resolver is not called. The check is done by matching the domain name against a regular expression, which is the value of this option. The default pattern is
dns_check_names_pattern = \ (?i)^(?>(?(1)\.|())[^\W_](?>[a-z0-9/-]*[^\W_])?)+$ |
which permits only letters, digits, slashes, and hyphens in components, but
they must start and end with a letter or digit. Hyphens are not, in fact,
permitted in host names, but they are found in certain NS records (which can be
accessed in Exim by using a dnsdb
lookup). If you set
allow_utf8_domains
, you must modify this pattern, or set the option to an
empty string.
| Use: main | Type: integer | Default: 5 |
This option controls the depth of parental searching for CSA SRV records in the DNS, as described in more detail in section Client SMTP authorization (CSA).
| Use: main | Type: boolean | Default: true |
This option controls whether or not an IP address, given as a CSA domain, is reversed and looked up in the reverse DNS, as described in more detail in section Client SMTP authorization (CSA).
| Use: main | Type: domain list* | Default: unset |
When Exim is compiled with IPv6 support and disable_ipv6
is not set, it
looks for IPv6 address records (AAAA records) as well as IPv4 address records
(A records) when trying to find IP addresses for hosts, unless the host's
domain matches this list.
This is a fudge to help with name servers that give big delays or otherwise do not work for the AAAA record type. In due course, when the world's name servers have all been upgraded, there should be no need for this option.
| Use: main | Type: time | Default: 0s |
The options dns_retrans
and dns_retry
can be used to set the
retransmission and retry parameters for DNS lookups. Values of zero (the
defaults) leave the system default settings unchanged. The first value is the
time between retries, and the second is the number of retries. It isn't
totally clear exactly how these settings affect the total time a DNS lookup may
take. I haven't found any documentation about timeouts on DNS lookups; these
parameter values are available in the external resolver interface structure,
but nowhere does it seem to describe how they are used or what you might want
to set in them.
| Use: main | Type: integer | Default: 0 |
See dns_retrans
above.
| Use: main | Type: boolean | Default: false |
This is an obsolete option that is now a no-op. It used to affect the way Exim handled CR and LF characters in incoming messages. What happens now is described in section Line endings.
| Use: main | Type: boolean | Default: true |
Exim's transports have an option for adding an Envelope-to: header to a message when it is delivered, in exactly the same way as Return-path: is handled. Envelope-to: records the original recipient address from the messages's envelope that caused the delivery to happen. Such headers should not be present in incoming messages, and this option causes them to be removed at the time the message is received, to avoid any problems that might occur when a delivered message is subsequently sent on to some other recipient.
| Use: main | Type: string list* | Default: unset |
Setting this option causes Exim to send bcc copies of bounce messages that it generates to other addresses. Note: This does not apply to bounce messages coming from elsewhere. The value of the option is a colon-separated list of items. Each item consists of a pattern, terminated by white space, followed by a comma-separated list of email addresses. If a pattern contains spaces, it must be enclosed in double quotes.
Each pattern is processed in the same way as a single item in an address list (see section Address lists). When a pattern matches the recipient of the bounce message, the message is copied to the addresses on the list. The items are scanned in order, and once a matching one is found, no further items are examined. For example:
errors_copy = spqr@mydomain postmaster@mydomain.example :\ rqps@mydomain hostmaster@mydomain.example,\ postmaster@mydomain.example |
The address list is expanded before use. The expansion variables $local_part
and $domain
are set from the original recipient of the error message, and if
there was any wildcard matching in the pattern, the expansion
variables $0
, $1
, etc. are set in the normal way.
| Use: main | Type: string | Default: unset |
By default, Exim's bounce and delivery warning messages contain the header line
From: Mail Delivery System <Mailer-Daemon@qualify-domain> |
where qualify-domain is the value of the qualify_domain
option.
A warning message that is generated by the quota_warn_message
option in an
appendfile
transport may contain its own From: header line that
overrides the default.
Experience shows that people reply to bounce messages. If the
errors_reply_to
option is set, a Reply-To: header is added to bounce
and warning messages. For example:
errors_reply_to = postmaster@my.domain.example |
The value of the option is not expanded. It must specify a valid RFC 2822
address. However, if a warning message that is generated by the
quota_warn_message
option in an appendfile
transport contain its
own Reply-To: header line, the value of the errors_reply_to
option is
not used.
| Use: main | Type: string | Default: compile-time configured |
This option changes the gid under which Exim runs when it gives up root
privilege. The default value is compiled into the binary. The value of this
option is used only when exim_user
is also set. Unless it consists entirely
of digits, the string is looked up using getgrnam()
, and failure causes a
configuration error. See chapter Security considerations for a discussion of
security issues.
| Use: main | Type: string | Default: see below |
This option specifies the path name of the Exim binary, which is used when Exim
needs to re-exec itself. The default is set up to point to the file exim in
the directory configured at compile time by the BIN_DIRECTORY setting. It
is necessary to change exim_path
if, exceptionally, Exim is run from some
other place.
Warning: Do not use a macro to define the value of this option, because
you will break those Exim utilities that scan the configuration file to find
where the binary is. (They then use the -bP
option to extract option
settings such as the value of spool_directory
.)
| Use: main | Type: string | Default: compile-time configured |
This option changes the uid under which Exim runs when it gives up root
privilege. The default value is compiled into the binary. Ownership of the run
time configuration file and the use of the -C
and -D
command line
options is checked against the values in the binary, not what is set here.
Unless it consists entirely of digits, the string is looked up using
getpwnam()
, and failure causes a configuration error. If exim_group
is
not also supplied, the gid is taken from the result of getpwnam()
if it is
used. See chapter Security considerations for a discussion of security issues.
| Use: main | Type: string list | Default: unset |
This option defines network interfaces that are to be considered local when routing, but which are not used for listening by the daemon. See section Recognising the local host for details.
| Use: main | Type: boolean | Default: true |
According to some Sendmail documentation (Sun, IRIX, HP-UX), if any addresses
are present on the command line when the -t
option is used to build an
envelope from a message's To:, Cc: and Bcc: headers, the command
line addresses are removed from the recipients list. This is also how Smail
behaves. However, other Sendmail documentation (the O'Reilly book) states that
command line addresses are added to those obtained from the header lines. When
extract_addresses_remove_arguments
is true (the default), Exim subtracts
argument headers. If it is set false, Exim adds rather than removes argument
addresses.
| Use: main | Type: integer | Default: 0 |
On systems running NIS or other schemes in which user and group information is
distributed from a remote system, there can be times when getpwnam()
and
related functions fail, even when given valid data, because things time out.
Unfortunately these failures cannot be distinguished from genuine "not found"
errors. If finduser_retries
is set greater than zero, Exim will try that
many extra times to find a user or a group, waiting for one second between
retries.
You should not set this option greater than zero if your user information is in a traditional `/etc/passwd' file, because it will cause Exim needlessly to search the file multiple times for non-existent users, and also cause delay.
| Use: main | Type: string list, comma separated | Default: unset |
On encountering certain errors, or when configured to do so in a system filter,
ACL, or special router, Exim freezes a message. This means that no further
delivery attempts take place until an administrator thaws the message, or the
auto_thaw
, ignore_bounce_errors_after
, or timeout_frozen_after
feature cause it to be processed. If freeze_tell
is set, Exim generates a
warning message whenever it freezes something, unless the message it is
freezing is a locally-generated bounce message. (Without this exception there
is the possibility of looping.) The warning message is sent to the addresses
supplied as the comma-separated value of this option. If several of the
message's addresses cause freezing, only a single message is sent. If the
freezing was automatic, the reason(s) for freezing can be found in the message
log. If you configure freezing in a filter or ACL, you must arrange for any
logging that you require.
| Use: main | Type: string* | Default: unset |
Some operating systems, notably HP-UX, use the "gecos" field in the system
password file to hold other information in addition to users' real names. Exim
looks up this field for use when it is creating Sender: or From:
headers. If either gecos_pattern
or gecos_name
are unset, the contents
of the field are used unchanged, except that, if an ampersand is encountered,
it is replaced by the user's login name with the first character forced to
upper case, since this is a convention that is observed on many systems.
When these options are set, gecos_pattern
is treated as a regular
expression that is to be applied to the field (again with & replaced by the
login name), and if it matches, gecos_name
is expanded and used as the
user's name.
Numeric variables such as $1
, $2
, etc. can be used in the expansion to
pick up sub-fields that were matched by the pattern. In HP-UX, where the user's
name terminates at the first comma, the following can be used:
gecos_pattern = ([^,]*) gecos_name = $1 |
| Use: main | Type: string | Default: unset |
See gecos_name
above.
| Use: main | Type: string | Default: see below |
This option sets a default character set for translating from encoded MIME
"words" in header lines, when referenced by an $h_xxx
expansion item. The
default is the value of HEADERS_CHARSET in `Local/Makefile'. The
ultimate default is ISO-8859-1. For more details see the description of header
insertions in section Expansion items.
| Use: main | Type: integer | Default: see below |
This option controls the overall maximum size of a message's header section. The default is the value of HEADER_MAXSIZE in `Local/Makefile'; the default for that is 1M. Messages with larger header sections are rejected.
| Use: main | Type: integer | Default: 0 |
This option limits the length of any individual header line in a message, after all the continuations have been joined together. Messages with individual header lines that are longer than the limit are rejected. The default value of zero means "no limit".
| Use: main | Type: host list* | Default: unset |
Exim checks the syntax of HELO and EHLO commands for incoming SMTP
mail, and gives an error response for invalid data. Unfortunately, there are
some SMTP clients that send syntactic junk. They can be accommodated by setting
this option. Note that this is a syntax check only. See helo_verify_hosts
if you want to do semantic checking.
See also helo_allow_chars
for a way of extending the permitted character
set.
| Use: main | Type: string | Default: unset |
This option can be set to a string of rogue characters that are permitted in all EHLO and HELO names in addition to the standard letters, digits, hyphens, and dots. If you really must allow underscores, you can set
helo_allow_chars = _ |
Note that the value is one string, not a list.
| Use: main | Type: domain list* | Default: `@:@[]' |
If the domain given by a client in a HELO or EHLO command matches this list, a reverse lookup is done in order to establish the host's true name. The default forces a lookup if the client host gives the server's name or any of its IP addresses (in brackets), something that broken clients have been seen to do.
| Use: main | Type: host list* | Default: unset |
By default, Exim just checks the syntax of HELO and EHLO commands (see
helo_accept_junk_hosts
and helo_allow_chars
). However, some sites like
to do more extensive checking of the data supplied by these commands. The ACL
condition `verify' `=' `helo' is provided to make this possible.
Formerly, it was necessary also to set this option (helo_try_verify_hosts
)
to force the check to occur. From release 4.53 onwards, this is no longer
necessary. If the check has not been done before `verify' `=' `helo' is
encountered, it is done at that time. Consequently, this option is obsolete.
Its specification is retained here for backwards compatibility.
When an EHLO or HELO command is received, if the calling host matches
helo_try_verify_hosts
, Exim checks that the host name given in the HELO or
EHLO command either:
gethostbyname()
(or getipnodebyname()
when
available) yields the calling host address.
However, the EHLO or HELO command is not rejected if any of the checks fail. Processing continues, but the result of the check is remembered, and can be detected later in an ACL by the `verify' `=' `helo' condition.
| Use: main | Type: host list* | Default: unset |
Like helo_try_verify_hosts
, this option is obsolete, and retained only for
backwards compatibility. For hosts that match this option, Exim checks the host
name given in the HELO or EHLO in the same way as for
helo_try_verify_hosts
. If the check fails, the HELO or EHLO command is
rejected with a 550 error, and entries are written to the main and reject logs.
If a MAIL command is received before EHLO or HELO, it is rejected with a 503
error.
| Use: main | Type: domain list* | Default: unset |
This option allows mail for particular domains to be held on the queue
manually. The option is overridden if a message delivery is forced with the
-M
, -qf
, -Rf
or -Sf
options, and also while testing or
verifying addresses using -bt
or -bv
. Otherwise, if a domain matches an
item in hold_domains
, no routing or delivery for that address is done, and
it is deferred every time the message is looked at.
This option is intended as a temporary operational measure for delaying the
delivery of mail while some problem is being sorted out, or some new
configuration tested. If you just want to delay the processing of some
domains until a queue run occurs, you should use queue_domains
or
queue_smtp_domains
, not hold_domains
.
A setting of hold_domains
does not override Exim's code for removing
messages from the queue if they have been there longer than the longest retry
time in any retry rule. If you want to hold messages for longer than the normal
retry times, insert a dummy retry rule with a long retry time.
| Use: main | Type: host list* | Default: unset |
Exim does not look up the name of a calling host from its IP address unless it
is required to compare against some host list, or the host matches
helo_try_verify_hosts
or helo_verify_hosts
, or the host matches this
option (which normally contains IP addresses rather than host names). The
default configuration file contains
host_lookup = * |
which causes a lookup to happen for all hosts. If the expense of these lookups is felt to be too great, the setting can be changed or removed.
After a successful reverse lookup, Exim does a forward lookup on the name it has obtained, to verify that it yields the IP address that it started with. If this check fails, Exim behaves as if the name lookup failed.
After any kind of failure, the host name (in $sender_host_name
) remains
unset, and $host_lookup_failed
is set to the string "1". See also
dns_again_means_nonexist
, helo_lookup_domains
, and `verify' `='
`reverse_host_lookup' in ACLs.
| Use: main | Type: string list | Default: `bydns:byaddr' |
This option specifies the order of different lookup methods when Exim is trying
to find a host name from an IP address. The default is to do a DNS lookup
first, and then to try a local lookup (using gethostbyaddr()
or equivalent)
if that fails. You can change the order of these lookups, or omit one entirely,
if you want.
Warning: The "byaddr" method does not always yield aliases when there are multiple PTR records in the DNS and the IP address is not listed in `/etc/hosts'. Different operating systems give different results in this case. That is why the default tries a DNS lookup first.
| Use: main | Type: host list* | Default: unset |
If this option is set, incoming SMTP calls from the hosts listed are rejected
as soon as the connection is made.
This option is obsolete, and retained only for backward compatibility, because
nowadays the ACL specified by acl_smtp_connect
can also reject incoming
connections immediately.
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, sometimes without much delay. Normally, it is better to use an ACL to reject incoming messages at a later stage, such as after RCPT commands. See chapter Access control lists.
| Use: main | Type: host list* | Default: unset |
This option defines a list of hosts for which connection logging does not
happen, even though the smtp_connection
log selector is set. For example,
you might want not to log SMTP connections from local processes, or from
127.0.0.1, or from your local LAN. This option is consulted in the main loop of
the daemon; you should therefore strive to restrict its value to a short inline
list of IP addresses and networks. To disable logging SMTP connections from
local processes, you must create a host list with an empty item. For example:
hosts_connection_nolog = : |
If the smtp_connection
log selector is not set, this option has no effect.
| Use: main | Type: domain list* | Default: unset |
If this option is set, any host names that match the domain list are treated as if they were the local host when Exim is scanning host lists obtained from MX records or other sources. Note that the value of this option is a domain list, not a host list, because it is always used to check host names, not IP addresses.
This option also applies when Exim is matching the special items
`@mx_any', `@mx_primary', and `@mx_secondary' in a domain list (see
section Domain lists), and when checking the hosts
option in the
smtp
transport for the local host (see the allow_localhost
option in
that transport). See also local_interfaces
, extra_local_interfaces
, and
chapter Starting the daemon and the use of network interfaces, which contains a discussion about local network
interfaces and recognising the local host.
| Use: main | Type: time | Default: 10w |
This option affects the processing of bounce messages that cannot be delivered, that is, those that suffer a permanent delivery failure. (Bounce messages that suffer temporary delivery failures are of course retried in the usual way.)
After a permanent delivery failure, bounce messages are frozen, because there is no sender to whom they can be returned. When a frozen bounce message has been on the queue for more than the given time, it is unfrozen at the next queue run, and a further delivery is attempted. If delivery fails again, the bounce message is discarded. This makes it possible to keep failed bounce messages around for a shorter time than the normal maximum retry time for frozen messages. For example,
ignore_bounce_errors_after = 12h |
retries failed bounce message deliveries after 12 hours, discarding any further
failures. If the value of this option is set to a zero time period, bounce
failures are discarded immediately. Setting a very long time (as in the default
value) has the effect of disabling this option. For ways of automatically
dealing with other kinds of frozen message, see auto_thaw
and
timeout_frozen_after
.
| Use: main | Type: host list* | Default: unset |
Some broken SMTP clients insist on sending a UUCP-like "From " line before
the headers of a message. By default this is treated as the start of the
message's body, which means that any following headers are not recognized as
such. Exim can be made to ignore it by setting ignore_fromline_hosts
to
match those hosts that insist on sending it. If the sender is actually a local
process rather than a remote host, and is using -bs
to inject the messages,
ignore_fromline_local
must be set to achieve this effect.
| Use: main | Type: boolean | Default: false |
See ignore_fromline_hosts
above.
| Use: main | Type: time | Default: 4d |
This option specifies the length of time to keep messages whose spool files have been corrupted in some way. This should, of course, never happen. At the next attempt to deliver such a message, it gets removed. The incident is logged.
| Use: main | Type: string list | Default: unset |
This option provides a list of LDAP servers which are tried in turn when an LDAP query does not contain a server. See section Format of LDAP queries for details of LDAP queries. This option is available only when Exim has been built with LDAP support.
| Use: main | Type: integer | Default: unset |
This option can be used to force Exim to set a specific protocol version for
LDAP. If it option is unset, it is shown by the -bP
command line option as
-1. When this is the case, the default is 3 if LDAP_VERSION3 is defined in
the LDAP headers; otherwise it is 2. This option is available only when Exim
has been built with LDAP support.
| Use: main | Type: boolean | Default: true |
When a message is submitted locally (that is, not over a TCP/IP connection) by
an untrusted user, Exim removes any existing Sender: header line, and
checks that the From: header line matches the login of the calling user and
the domain specified by qualify_domain
.
Note: An unqualified address (no domain) in the From: header in a
locally submitted message is automatically qualified by Exim, unless the
-bnq
command line option is used.
You can use local_from_prefix
and local_from_suffix
to permit affixes
on the local part. If the From: header line does not match, Exim adds a
Sender: header with an address constructed from the calling user's login
and the default qualify domain.
If local_from_check
is set false, the From: header check is disabled,
and no Sender: header is ever added. If, in addition, you want to retain
Sender: header lines supplied by untrusted users, you must also set
local_sender_retain
to be true.
These options affect only the header lines in the message. The envelope sender
is still forced to be the login id at the qualify domain unless
untrusted_set_sender
permits the user to supply an envelope sender.
For messages received over TCP/IP, an ACL can specify "submission mode" to request similar header line checking. See section The Sender: header line, which has more details about Sender: processing.
| Use: main | Type: string | Default: unset |
When Exim checks the From: header line of locally submitted messages for
matching the login id (see local_from_check
above), it can be configured to
ignore certain prefixes and suffixes in the local part of the address. This is
done by setting local_from_prefix
and/or local_from_suffix
to
appropriate lists, in the same form as the local_part_prefix
and
local_part_suffix
router options (see chapter Generic options for routers). For
example, if
local_from_prefix = *- |
is set, a From: line containing
From: anything-user@your.domain.example |
will not cause a Sender: header to be added if user@your.domain.example matches the actual sender address that is constructed from the login name and qualify domain.
| Use: main | Type: string | Default: unset |
See local_from_prefix
above.
| Use: main | Type: string list | Default: see below |
This option controls which network interfaces are used by the daemon for
listening; they are also used to identify the local host when routing. Chapter
Starting the daemon and the use of network interfaces contains a full description of this option and the related
options daemon_smtp_ports
, extra_local_interfaces
,
hosts_treat_as_local
, and tls_on_connect_ports
. The default value for
local_interfaces
is
local_interfaces = 0.0.0.0 |
when Exim is built without IPv6 support; otherwise it is
local_interfaces = <; ::0 ; 0.0.0.0 |
| Use: main | Type: time | Default: 5m |
This timeout applies to the local_scan()
function (see chapter
Adding a local scan function to Exim). Zero means "no timeout". If the timeout is exceeded,
the incoming message is rejected with a temporary error if it is an SMTP
message. For a non-SMTP message, the message is dropped and Exim ends with a
non-zero code. The incident is logged on the main and reject logs.
| Use: main | Type: boolean | Default: false |
When a message is submitted locally (that is, not over a TCP/IP connection) by
an untrusted user, Exim removes any existing Sender: header line. If you
do not want this to happen, you must set local_sender_retain
, and you must
also set local_from_check
to be false (Exim will complain if you do not).
See also the ACL modifier `control = suppress_local_fixups'. Section
The Sender: header line has more details about Sender: processing.
| Use: main | Type: string* | Default: unset |
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
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
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 Message identification.
| Use: main | Type: string list* | Default: set at compile time |
This option sets the path which is used to determine the names of Exim's log
files, or indicates that logging is to be to syslog, or both. It is expanded
when Exim is entered, so it can, for example, contain a reference to the host
name. If no specific path is set for the log files at compile or run time, they
are written in a sub-directory called `log' in Exim's spool directory.
Chapter Log files contains further details about Exim's logging, and
section Where the logs are written describes how the contents of log_file_path
are
used. If this string is fixed at your installation (contains no expansion
variables) it is recommended that you do not set this option in the
configuration file, but instead supply the path using LOG_FILE_PATH in
`Local/Makefile' so that it is available to Exim for logging errors detected
early on - in particular, failure to read the configuration file.
| Use: main | Type: string | Default: unset |
This option can be used to reduce or increase the number of things that Exim writes to its log files. Its argument is made up of names preceded by plus or minus characters. For example:
log_selector = +arguments -retry_defer |
A list of possible names and what they control is given in the chapter on logging, in section Reducing or increasing what is logged.
| Use: main | Type: boolean | Default: false |
By default, the timestamps on log lines are in local time without the
timezone. This means that if your timezone changes twice a year, the timestamps
in log lines are ambiguous for an hour when the clocks go back. One way of
avoiding this problem is to set the timezone to UTC. An alternative is to set
log_timezone
true. This turns on the addition of the timezone offset to
timestamps in log lines. Turning on this option can add quite a lot to the size
of log files because each line is extended by 6 characters. Note that the
$tod_log
variable contains the log timestamp without the zone, but there is
another variable called $tod_zone
that contains just the timezone offset.
| Use: main | Type: integer | Default: 25 |
This option limits the number of simultaneously open files for single-key
lookups that use regular files (that is, lsearch
, dbm
, and cdb
).
Exim normally keeps these files open during routing, because often the same
file is required several times. If the limit is reached, Exim closes the least
recently used file. Note that if you are using the ndbm library, it
actually opens two files for each logical DBM database, though it still counts
as one for the purposes of lookup_open_max
. If you are getting "too many
open files" errors with NDBM, you need to reduce the value of
lookup_open_max
.
| Use: main | Type: integer | Default: 0 |
Some operating systems are broken in that they truncate long arguments to
getpwnam()
to eight characters, instead of returning "no such user". If
this option is set greater than zero, any attempt to call getpwnam()
with
an argument that is longer behaves as if getpwnam()
failed.
| Use: main | Type: integer | Default: 500 |
This option specifies how much of a message's body is to be included in the
$message_body
and $message_body_end
expansion variables.
| Use: main | Type: string* | Default: unset |
If this option is set, the string is expanded and used as the right hand side (domain) of the Message-ID: header that Exim creates if a locally-originated incoming message does not have one. "Locally-originated" means "not received over TCP/IP." Otherwise, the primary host name is used. Only letters, digits, dot and hyphen are accepted; any other characters are replaced by hyphens. If the expansion is forced to fail, or if the result is an empty string, the option is ignored.
| Use: main | Type: string* | Default: unset |
If this variable is set, the string is expanded and used to augment the text of
the Message-id: header that Exim creates if a locally-originated incoming
message does not have one. The text of this header is required by RFC 2822 to
take the form of an address. By default, Exim uses its internal message id as
the local part, and the primary host name as the domain. If this option is set,
it is expanded, and provided the expansion is not forced to fail, and does not
yield an empty string, the result is inserted into the header immediately
before the @, separated from the internal message id by a dot. Any characters
that are illegal in an address are automatically converted into hyphens. This
means that variables such as $tod_log
can be used, because the spaces and
colons will become hyphens.
| Use: main | Type: boolean | Default: true |
If this option is turned off, per-message log files are not created in the `msglog' spool sub-directory. This reduces the amount of disk I/O required by Exim, by reducing the number of files involved in handling a message from a minimum of four (header spool file, body spool file, delivery journal, and per-message log) to three. The other major I/O activity is Exim's main log, which is not affected by this option.
| Use: main | Type: string* | Default: 50M |
This option limits the maximum size of message that Exim will process. The
value is expanded for each incoming
connection so, for example, it can be made to depend on the IP address of the
remote host for messages arriving via TCP/IP. Note: This limit cannot be
made to depend on a message's sender or any other properties of an individual
message, because it has to be advertised in the server's response to EHLO.
String expansion failure causes a temporary error. A value of zero means no
limit, but its use is not recommended. See also bounce_return_size_limit
.
Incoming SMTP messages are failed with a 552 error if the limit is
exceeded; locally-generated messages either get a stderr message or a delivery
failure message to the sender, depending on the -oe
setting. Rejection of
an oversized message is logged in both the main and the reject logs. See also
the generic transport option message_size_limit
, which limits the size of
message that an individual transport can process.
| Use: main | Type: boolean | Default: false |
This option, which is available only if Exim has been built with the setting
SUPPORT_MOVE_FROZEN_MESSAGES=yes |
in `Local/Makefile', causes frozen messages and their message logs to be
moved from the `input' and `msglog' directories on the spool to `Finput'
and `Fmsglog', respectively. There is currently no support in Exim or the
standard utilities for handling such moved messages, and they do not show up in
lists generated by -bp
or by the Exim monitor.
| Use: main | Type: boolean | Default: false |
Setting this option true causes Exim to run in a very restrictive mode in which it passes messages synchronously to a smart host. Chapter Using Exim as a non-queueing client contains a full description of this facility.
| Use: main | Type: string list | Default: unset |
This option provides a list of MySQL servers and associated connection data, to
be used in conjunction with mysql
lookups (see section SQL lookups). The
option is available only if Exim has been built with MySQL support.
| Use: main | Type: string list* | Default: unset |
This option is expanded just once, at the start of Exim's processing. Local message deliveries are normally run in processes that are setuid to the recipient, and remote deliveries are normally run under Exim's own uid and gid. It is usually desirable to prevent any deliveries from running as root, as a safety precaution.
When Exim is built, an option called FIXED_NEVER_USERS can be set to a
list of users that must not be used for local deliveries. This list is fixed in
the binary and cannot be overridden by the configuration file. By default, it
contains just the single user name "root". The never_users
runtime option
can be used to add more users to the fixed list.
If a message is to be delivered as one of the users on the fixed list or the
never_users
list, an error occurs, and delivery is deferred. A common
example is
never_users = root:daemon:bin |
Including root is redundant if it is also on the fixed list, but it does no
harm. This option overrides the pipe_as_creator
option of the pipe
transport driver.
| Use: main | Type: string list | Default: unset |
This option provides a list of Oracle servers and associated connection data,
to be used in conjunction with oracle
lookups (see section SQL lookups).
The option is available only if Exim has been built with Oracle support.
| Use: main | Type: domain list* | Default: unset |
The "percent hack" is the convention whereby a local part containing a percent sign is re-interpreted as a new email address, with the percent replaced by @. This is sometimes called "source routing", though that term is also applied to RFC 2822 addresses that begin with an @ character. If this option is set, Exim implements the percent facility for those domains listed, but no others. This happens before an incoming SMTP address is tested against an ACL.
Warning: The "percent hack" has often been abused by people who are trying to get round relaying restrictions. For this reason, it is best avoided if at all possible. Unfortunately, a number of less security-conscious MTAs implement it unconditionally. If you are running Exim on a gateway host, and routing mail through to internal MTAs without processing the local parts, it is a good idea to reject recipient addresses with percent characters in their local parts. Exim's default configuration does this.
| Use: main | Type: boolean | Default: false |
This option is available only when Exim is built with an embedded Perl interpreter. See chapter Embedded Perl for details of its use.
| Use: main | Type: string | Default: unset |
This option is available only when Exim is built with an embedded Perl interpreter. See chapter Embedded Perl for details of its use.
| Use: main | Type: string list | Default: unset |
This option provides a list of PostgreSQL servers and associated connection
data, to be used in conjunction with pgsql
lookups (see section
SQL lookups). The option is available only if Exim has been built with
PostgreSQL support.
| Use: main | Type: string* | Default: set at compile time |
This option sets the name of the file to which the Exim daemon writes its process id. The string is expanded, so it can contain, for example, references to the host name:
pid_file_path = /var/log/$primary_hostname/exim.pid |
If no path is set, the pid is written to the file `exim-daemon.pid' in Exim's
spool directory.
The value set by the option can be overridden by the -oP
command line
option. A pid file is not written if a "non-standard" daemon is run by means
of the -oX
option, unless a path is explicitly supplied by -oP
.
| Use: main | Type: host list* | Default: * |
This option can be used to suppress the advertisement of the SMTP
PIPELINING extension to specific hosts. When PIPELINING is not
advertised and smtp_enforce_sync
is true, an Exim server enforces strict
synchronization for each SMTP command and response.
When PIPELINING is advertised, Exim assumes that clients will use it; "out
of order" commands that are "expected" do not count as protocol errors (see
smtp_max_synprot_errors
).
| Use: main | Type: boolean | Default: false |
If this option is set, message log files are not deleted when messages are completed. Instead, they are moved to a sub-directory of the spool directory called `msglog.OLD', where they remain available for statistical or debugging purposes. This is a dangerous option to set on systems with any appreciable volume of mail. Use with care!
| Use: main | Type: string | Default: see below |
This specifies the name of the current host. It is used in the default EHLO or
HELO command for outgoing SMTP messages (changeable via the helo_data
option in the smtp
transport), and as the default for qualify_domain
.
The value is also used by default in some SMTP response messages from an Exim
server. This can be changed dynamically by setting smtp_active_hostname
.
If primary_hostname
is not set, Exim calls uname()
to find the host
name. If this fails, Exim panics and dies. If the name returned by uname()
contains only one component, Exim passes it to gethostbyname()
(or
getipnodebyname()
when available) in order to obtain the fully qualified
version. The variable $primary_hostname
contains the host name, whether set
explicitly by this option, or defaulted.
| Use: main | Type: boolean | Default: false |
By default, Exim considers only those characters whose codes lie in the range
32-126 to be printing characters. In a number of circumstances (for example,
when writing log entries) non-printing characters are converted into escape
sequences, primarily to avoid messing up the layout. If print_topbitchars
is set, code values of 128 and above are also considered to be printing
characters.
This option also affects the header syntax checks performed by the
autoreply
transport, and whether Exim uses RFC 2047 encoding of
the user's full name when constructing From: and Sender: addresses (as
described in section Constructed addresses). Setting this option can cause
Exim to generate eight bit message headers that do not conform to the
standards.
| Use: main | Type: string | Default: unset |
This option sets the name of the file to which an Exim process writes its "process log" when sent a USR1 signal. This is used by the exiwhat utility script. If this option is unset, the file called `exim-process.info' in Exim's spool directory is used. The ability to specify the name explicitly can be useful in environments where two different Exims are running, using different spool directories.
| Use: main | Type: boolean | Default: true |
The -M
, -R
, and -q
command-line options require the caller to be an
admin user unless prod_requires_admin
is set false. See also
queue_list_requires_admin
.
| Use: main | Type: string | Default: see below |
This option specifies the domain name that is added to any envelope sender
addresses that do not have a domain qualification. It also applies to
recipient addresses if qualify_recipient
is not set. Unqualified addresses
are accepted by default only for locally-generated messages. Qualification is
also applied to addresses in header lines such as From: and To: for
locally-generated messages, unless the -bnq
command line option is used.
Messages from external sources must always contain fully qualified addresses,
unless the sending host matches sender_unqualified_hosts
or
recipient_unqualified_hosts
(as appropriate), in which case incoming
addresses are qualified with qualify_domain
or qualify_recipient
as
necessary. Internally, Exim always works with fully qualified envelope
addresses. If qualify_domain
is not set, it defaults to the
primary_hostname
value.
| Use: main | Type: string | Default: see below |
This option allows you to specify a different domain for qualifying recipient
addresses to the one that is used for senders. See qualify_domain
above.
| Use: main | Type: domain list* | Default: unset |
This option lists domains for which immediate delivery is not required.
A delivery process is started whenever a message is received, but only those
domains that do not match are processed. All other deliveries wait until the
next queue run. See also hold_domains
and queue_smtp_domains
.
| Use: main | Type: boolean | Default: true |
The -bp
command-line option, which lists the messages that are on the
queue, requires the caller to be an admin user unless
queue_list_requires_admin
is set false. See also prod_requires_admin
.
| Use: main | Type: boolean | Default: false |
If queue_only
is set, a delivery process is not automatically started
whenever a message is received. Instead, the message waits on the queue for the
next queue run. Even if queue_only
is false, incoming messages may not get
delivered immediately when certain conditions (such as heavy load) occur.
The -odq
command line has the same effect as queue_only
. The -odb
and -odi
command line options override queue_only
unless
queue_only_override
is set false. See also queue_only_file
,
queue_only_load
, and smtp_accept_queue
.
| Use: main | Type: string | Default: unset |
This option can be set to a colon-separated list of absolute path names, each
one optionally preceded by "smtp". When Exim is receiving a message,
it tests for the existence of each listed path using a call to stat()
. For
each path that exists, the corresponding queuing option is set.
For paths with no prefix, queue_only
is set; for paths prefixed by
"smtp", queue_smtp_domains
is set to match all domains. So, for example,
queue_only_file = smtp/some/file |
causes Exim to behave as if queue_smtp_domains
were set to "*" whenever
`/some/file' exists.
| Use: main | Type: fixed-point | Default: unset |
If the system load average is higher than this value, incoming messages from
all sources are queued, and no automatic deliveries are started. If this
happens during local or remote SMTP input, all subsequent messages on the same
connection are queued. Deliveries will subsequently be performed by queue
runner processes. This option has no effect on ancient operating systems on
which Exim cannot determine the load average. See also
deliver_queue_load_max
and smtp_load_reserve
.
| Use: main | Type: boolean | Default: true |
When this option is true, the -od
x command line options override the
setting of queue_only
or queue_only_file
in the configuration file. If
queue_only_override
is set false, the -od
x options cannot be used
to override; they are accepted, but ignored.
| Use: main | Type: boolean | Default: false |
If this option is set, queue runs happen in order of message arrival instead of
in an arbitrary order. For this to happen, a complete list of the entire queue
must be set up before the deliveries start. When the queue is all held in a
single directory (the default), a single list is created for both the ordered
and the non-ordered cases. However, if split_spool_directory
is set, a
single list is not created when queue_run_in_order
is false. In this case,
the sub-directories are processed one at a time (in a random order), and this
avoids setting up one huge list for the whole queue. Thus, setting
queue_run_in_order
with split_spool_directory
may degrade performance
when the queue is large, because of the extra work in setting up the single,
large list. In most situations, queue_run_in_order
should not be set.
| Use: main | Type: integer | Default: 5 |
This controls the maximum number of queue runner processes that an Exim daemon can run simultaneously. This does not mean that it starts them all at once, but rather that if the maximum number are still running when the time comes to start another one, it refrains from starting another one. This can happen with very large queues and/or very sluggish deliveries. This option does not, however, interlock with other processes, so additional queue runners can be started by other means, or by killing and restarting the daemon.
Setting this option to zero does not suppress queue runs; rather, it disables
the limit, allowing any number of simultaneous queue runner processes to be
run. If you do not want queue runs to occur, omit the -q
xx setting on
the daemon's command line.
| Use: main | Type: domain list* | Default: unset |
When this option is set, a delivery process is started whenever a message is
received, routing is performed, and local deliveries take place.
However, if any SMTP deliveries are required for domains that match
queue_smtp_domains
, they are not immediately delivered, but instead the
message waits on the queue for the next queue run. Since routing of the message
has taken place, Exim knows to which remote hosts it must be delivered, and so
when the queue run happens, multiple messages for the same host are delivered
over a single SMTP connection. The -odqs
command line option causes all
SMTP deliveries to be queued in this way, and is equivalent to setting
queue_smtp_domains
to "*". See also hold_domains
and
queue_domains
.
| Use: main | Type: time | Default: 0s |
This option sets the timeout for accepting a non-SMTP message, that is, the
maximum time that Exim waits when reading a message on the standard input. If
the value is zero, it will wait for ever. This setting is overridden by the
-or
command line option. The timeout for incoming SMTP messages is
controlled by smtp_receive_timeout
.
| Use: main | Type: string* | Default: see below |
This string defines the contents of the Received: message header that is added to each message, except for the timestamp, which is automatically added on at the end (preceded by a semicolon). The string is expanded each time it is used. If the expansion yields an empty string, no Received: header line is added to the message. Otherwise, the string should start with the text "Received:" and conform to the RFC 2822 specification for Received: header lines. The default setting is:
received_header_text = Received: \ ${if def:sender_rcvhost {from $sender_rcvhost\n\t}\ {${if def:sender_ident \ {from ${quote_local_part:$sender_ident} }}\ ${if def:sender_helo_name {(helo=$sender_helo_name)\n\t}}}}\ by $primary_hostname \ ${if def:received_protocol {with $received_protocol}} \ ${if def:tls_cipher {($tls_cipher)\n\t}}\ (Exim $version_number)\n\t\ ${if def:sender_address \ {(envelope-from <$sender_address>)\n\t}}\ id $message_exim_id\ ${if def:received_for {\n\tfor $received_for}} |
The reference to the TLS cipher is omitted when Exim is built without TLS support. The use of conditional expansions ensures that this works for both locally generated messages and messages received from remote hosts, giving header lines such as the following:
Received: from scrooge.carol.example ([192.168.12.25] ident=root) by marley.carol.example with esmtp (Exim 4.00) (envelope-from <bob@carol.example>) id 16IOWa-00019l-00 for chas@dickens.example; Tue, 25 Dec 2001 14:43:44 +0000 Received: by scrooge.carol.example with local (Exim 4.00) id 16IOWW-000083-00; Tue, 25 Dec 2001 14:43:41 +0000 |
Until the body of the message has been received, the timestamp is the time when the message started to be received. Once the body has arrived, and all policy checks have taken place, the timestamp is updated to the time at which the message was accepted.
| Use: main | Type: integer | Default: 30 |
When a message is to be delivered, the number of Received: headers is counted, and if it is greater than this parameter, a mail loop is assumed to have occurred, the delivery is abandoned, and an error message is generated. This applies to both local and remote deliveries.
| Use: main | Type: host list* | Default: unset |
This option lists those hosts from which Exim is prepared to accept unqualified
recipient addresses in message envelopes. The addresses are made fully
qualified by the addition of the qualify_recipient
value. This option also
affects message header lines. Exim does not reject unqualified recipient
addresses in headers, but it qualifies them only if the message came from a
host that matches recipient_unqualified_hosts
,
or if the message was submitted locally (not using TCP/IP), and the -bnq
option was not set.
| Use: main | Type: integer | Default: 0 |
If 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.
Note: The RFCs specify that an SMTP server should accept at least 100 RCPT commands in a single message.
| Use: main | Type: boolean | Default: false |
If this option is set true, Exim rejects SMTP messages containing too many recipients by giving 552 errors to the surplus RCPT commands, and a 554 error to the eventual DATA command. Otherwise (the default) it gives a 452 error to the surplus RCPT commands and accepts the message on behalf of the initial set of recipients. The remote server should then re-send the message for the remaining recipients at a later time.
| Use: main | Type: integer | Default: 2 |
This option controls parallel delivery of one message to a number of remote
hosts. If the value is less than 2, parallel delivery is disabled, and Exim
does all the remote deliveries for a message one by one. Otherwise, if a single
message has to be delivered to more than one remote host, or if several copies
have to be sent to the same remote host, up to remote_max_parallel
deliveries are done simultaneously. If more than remote_max_parallel
deliveries are required, the maximum number of processes are started, and as
each one finishes, another is begun. The order of starting processes is the
same as if sequential delivery were being done, and can be controlled by the
remote_sort_domains
option. If parallel delivery takes place while running
with debugging turned on, the debugging output from each delivery process is
tagged with its process id.
This option controls only the maximum number of parallel deliveries for one message in one Exim delivery process. Because Exim has no central queue manager, there is no way of controlling the total number of simultaneous deliveries if the configuration allows a delivery attempt as soon as a message is received.
If you want to control the total number of deliveries on the system, you
need to set the queue_only
option. This ensures that all incoming messages
are added to the queue without starting a delivery process. Then set up an Exim
daemon to start queue runner processes at appropriate intervals (probably
fairly often, for example, every minute), and limit the total number of queue
runners by setting the queue_run_max
parameter. Because each queue runner
delivers only one message at a time, the maximum number of deliveries that can
then take place at once is queue_run_max
multiplied by
remote_max_parallel
.
If it is purely remote deliveries you want to control, use
queue_smtp_domains
instead of queue_only
. This has the added benefit of
doing the SMTP routing before queuing, so that several messages for the same
host will eventually get delivered down the same connection.
| Use: main | Type: domain list* | Default: unset |
When there are a number of remote deliveries for a message, they are sorted by domain into the order given by this list. For example,
remote_sort_domains = *.cam.ac.uk:*.uk |
would attempt to deliver to all addresses in the cam.ac.uk domain first,
then to those in the uk
domain, then to any others.
| Use: main | Type: time | Default: 7d |
This option sets a "use before" time on retry information in Exim's hints database. Any older retry data is ignored. This means that, for example, once a host has not been tried for 7 days, Exim behaves as if it has no knowledge of past failures.
| Use: main | Type: time | Default: 24h |
Chapter Retry configuration describes Exim's mechanisms for controlling the intervals between delivery attempts for messages that cannot be delivered straight away. This option sets an overall limit to the length of time between retries. It cannot be set greater than 24 hours; any attempt to do so forces the default value.
| Use: main | Type: boolean | Default: true |
RFC 2821, section 4.4, states that an SMTP server must insert a
Return-path: header line into a message when it makes a "final delivery".
The Return-path: header preserves the sender address as received in the
MAIL command. This description implies that this header should not be present
in an incoming message. If return_path_remove
is true, any existing
Return-path: headers are removed from messages at the time they are
received. Exim's transports have options for adding Return-path: headers at
the time of delivery. They are normally used only for final local deliveries.
| Use: main | Type: integer | Default: 100K |
This option is an obsolete synonym for bounce_return_size_limit
.
| Use: main | Type: host list* | Default: * |
RFC 1413 identification calls are made to any client host which matches an item in the list.
| Use: main | Type: time | Default: 5s |
This sets the timeout on RFC 1413 identification calls. If it is set to zero, no RFC 1413 calls are ever made.
| Use: main | Type: host list* | Default: unset |
This option lists those hosts from which Exim is prepared to accept unqualified
sender addresses. The addresses are made fully qualified by the addition of
qualify_domain
. This option also affects message header lines. Exim does
not reject unqualified addresses in headers that contain sender addresses, but
it qualifies them only if the message came from a host that matches
sender_unqualified_hosts
, or if the message was submitted locally (not
using TCP/IP), and the -bnq
option was not set.
| Use: main | Type: boolean | Default: true |
This option controls the setting of the SO_KEEPALIVE option on incoming TCP/IP socket connections. When set, it causes the kernel to probe idle connections periodically, by sending packets with "old" sequence numbers. The other end of the connection should send an acknowledgement if the connection is still okay or a reset if the connection has been aborted. The reason for doing this is that it has the beneficial effect of freeing up certain types of connection that can get stuck when the remote host is disconnected without tidying up the TCP/IP call properly. The keepalive mechanism takes several hours to detect unreachable hosts.
| Use: main | Type: integer | Default: 20 |
This option specifies the maximum number of simultaneous incoming SMTP calls
that Exim will accept. It applies only to the listening daemon; there is no
control (in Exim) when incoming SMTP is being handled by inetd. If the
value is set to zero, no limit is applied. However, it is required to be
non-zero if either smtp_accept_max_per_host
or smtp_accept_queue
is
set. See also smtp_accept_reserve
.
| Use: main | Type: integer | Default: 10 |
Exim counts the number of "non-mail" commands in an SMTP session, and drops
the connection if there are too many. This option defines "too many". The
check catches some denial-of-service attacks, repeated failing AUTHs, or a mad
client looping sending EHLO, for example. The check is applied only if the
client host matches smtp_accept_max_nonmail_hosts
.
When a new message is expected, one occurrence of RSET is not counted. This allows a client to send one RSET between messages (this is not necessary, but some clients do it). Exim also allows one uncounted occurence of HELO or EHLO, and one occurrence of STARTTLS between messages. After starting up a TLS session, another EHLO is expected, and so it too is not counted. The first occurrence of AUTH in a connection, or immediately following STARTTLS is not counted. Otherwise, all commands other than MAIL, RCPT, DATA, and QUIT are counted.
| Use: main | Type: host list* | Default: * |
You can control which hosts are subject to the smtp_accept_max_nonmail
check by setting this option. The default value makes it apply to all hosts. By
changing the value, you can exclude any badly-behaved hosts that you have to
live with.
| Use: main | Type: integer | Default: 1000 |
The value of this option limits the number of MAIL commands that Exim is prepared to accept over a single SMTP connection, whether or not each command results in the transfer of a message. After the limit is reached, a 421 response is given to subsequent MAIL commands. This limit is a safety precaution against a client that goes mad (incidents of this type have been seen).
| Use: main | Type: string* | Default: unset |
This option restricts the number of simultaneous IP connections from a single
host (strictly, from a single IP address) to the Exim daemon. The option is
expanded, to enable different limits to be applied to different hosts by
reference to $sender_host_address
. Once the limit is reached, additional
connection attempts from the same host are rejected with error code 421. The
default value of zero imposes no limit. If this option is set, it is required
that smtp_accept_max
be non-zero.
Warning: When setting this option you should not use any expansion constructions that take an appreciable amount of time. The expansion and test happen in the main daemon loop, in order to reject additional connections without forking additional processes (otherwise a denial-of-service attack could cause a vast number or processes to be created). While the daemon is doing this processing, it cannot accept any other incoming connections.
| Use: main | Type: integer | Default: 0 |
If the number of simultaneous incoming SMTP calls handled via the listening
daemon exceeds this value, messages received by SMTP are just placed on the
queue; no delivery processes are started automatically. 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 also queue_only
,
queue_only_load
, queue_smtp_domains
, and the various -od
x
command line options.
| Use: main | Type: integer | Default: 10 |
This option limits the number of delivery processes that Exim starts
automatically when receiving messages via SMTP, whether via the daemon or by
the use of -bs
or -bS
. If the value of the option is greater than zero,
and the number of messages received in a single SMTP session exceeds this
number, subsequent messages are placed on the queue, but no delivery processes
are started. This helps to limit the number of Exim processes when a server
restarts after downtime and there is a lot of mail waiting for it on other
systems. On large systems, the default should probably be increased, and on
dial-in client systems it should probably be set to zero (that is, disabled).
| Use: main | Type: integer | Default: 0 |
When smtp_accept_max
is set greater than zero, this option specifies a
number of SMTP connections that are reserved for connections from the hosts
that are specified in smtp_reserve_hosts
. The value set in
smtp_accept_max
includes this reserve pool. The specified hosts are not
restricted to this number of connections; the option specifies a minimum number
of connection slots for them, not a maximum. It is a guarantee that that group
of hosts can always get at least smtp_accept_reserve
connections.
For example, if smtp_accept_max
is set to 50 and smtp_accept_reserve
is
set to 5, once there are 45 active connections (from any hosts), new
connections are accepted only from hosts listed in smtp_reserve_hosts
.
See also smtp_accept_max_per_host
.
| Use: main | Type: string* | Default: unset |
This option is provided for multi-homed servers that want to masquerade as
several different hosts. At the start of an SMTP connection, its value is
expanded and used instead of the value of $primary_hostname
in SMTP
responses. For example, it is used as domain name in the response to an
incoming HELO or EHLO command.
It is also used in HELO commands for callout verification. The active hostname
is placed in the $smtp_active_hostname
variable, which is saved with any
messages that are received. It is therefore available for use in routers and
transports when the message is later delivered.
If this option is unset, or if its expansion is forced to fail, or if the
expansion results in an empty string, the value of $primary_hostname
is
used. Other expansion failures cause a message to be written to the main and
panic logs, and the SMTP command receives a temporary error. Typically, the
value of smtp_active_hostname
depends on the incoming interface address.
For example:
smtp_active_hostname = ${if eq{$interface_address}{10.0.0.1}\ {cox.mydomain}{box.mydomain}} |
| Use: main | Type: string* | Default: see below |
This string, which is expanded every time it is used, is output as the initial positive response to an SMTP connection. The default setting is:
smtp_banner = $smtp_active_hostname ESMTP Exim \ $version_number $tod_full |
Failure to expand the string causes a panic error. 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 in this string. Exim adds it automatically (several times in the case of a multiline response).
| Use: main | Type: boolean | Default: true |
When this option is set, if an incoming SMTP session encounters the SIZE
option on a MAIL command, it checks that there is enough space in the
spool directory's partition to accept a message of that size, while still
leaving free the amount specified by check_spool_space
(even if that value
is zero). If there isn't enough space, a temporary error code is returned.
| Use: main | Type: integer | Default: 20 |
This option specifies a maximum number of waiting SMTP connections. Exim passes this value to the TCP/IP system when it sets up its listener. Once this number of connections are waiting for the daemon's attention, subsequent connection attempts are refused at the TCP/IP level. At least, that is what the manuals say; in some circumstances such connection attempts have been observed to time out instead. For large systems it is probably a good idea to increase the value (to 50, say). It also gives some protection against denial-of-service attacks by SYN flooding.
| Use: main | Type: boolean | Default: true |
The SMTP protocol specification requires the client to wait for a response from the server at certain points in the dialogue. Without PIPELINING these synchronization points are after every command; with PIPELINING they are fewer, but they still exist.
Some spamming sites send out a complete set of SMTP commands without waiting for any response. Exim protects against this by rejecting a message if the client has sent further input when it should not have. The error response "554 SMTP synchronization error" is sent, and the connection is dropped. Testing for this error cannot be perfect because of transmission delays (unexpected input may be on its way but not yet received when Exim checks). However, it does detect many instances.
The check can be globally disabled by setting smtp_enforce_sync
false.
If you want to disable the check selectively (for example, only for certain
hosts), you can do so by an appropriate use of a control
modifier in an ACL
(see section Use of the control modifier). See also pipelining_advertise_hosts
.
| Use: main | Type: string* | Default: unset |
If this option is set, the given command is run whenever an SMTP ETRN
command is received from a host that is permitted to issue such commands (see
chapter Access control lists). The string is split up into separate arguments which
are independently expanded. The expansion variable $domain
is set to the
argument of the ETRN command, and no syntax checking is done on it. For
example:
smtp_etrn_command = /etc/etrn_command $domain \ $sender_host_address |
A new process is created to run the command, but Exim does not wait for it to complete. Consequently, its status cannot be checked. If the command cannot be run, a line is written to the panic log, but the ETRN caller still receives a 250 success response. Exim is normally running under its own uid when receiving SMTP, so it is not possible for it to change the uid before running the command.
| Use: main | Type: boolean | Default: true |
When this option is set, it prevents the simultaneous execution of more than one identical command as a result of ETRN in an SMTP connection. See section The ETRN command for details.
| Use: main | Type: fixed-point | Default: unset |
If the system load average ever gets higher than this, incoming SMTP calls are
accepted only from those hosts that match an entry in smtp_reserve_hosts
.
If smtp_reserve_hosts
is not set, no incoming SMTP calls are accepted when
the load is over the limit. The option has no effect on ancient operating
systems on which Exim cannot determine the load average. See also
deliver_queue_load_max
and queue_only_load
.
| Use: main | Type: integer | Default: 3 |
Exim rejects SMTP commands that contain syntax or protocol errors. In particular, a syntactically invalid email address, as in this command:
RCPT TO:<abc xyz@a.b.c> |
causes immediate rejection of the command, before any other tests are done. (The ACL cannot be run if there is no valid address to set up for it.) An example of a protocol error is receiving RCPT before MAIL. If there are too many syntax or protocol errors in one SMTP session, the connection is dropped. The limit is set by this option.
When the PIPELINING extension to SMTP is in use, some protocol errors are
"expected", for instance, a RCPT command after a rejected MAIL command.
Exim assumes that PIPELINING will be used if it advertises it (see
pipelining_advertise_hosts
), and in this situation, "expected" errors do
not count towards the limit.
| Use: main | Type: integer | Default: 3 |
If there are too many unrecognized commands in an incoming SMTP session, an Exim server drops the connection. This is a defence against some kinds of abuse that subvert web clients into making connections to SMTP ports; in these circumstances, a number of non-SMTP command lines are sent first.
| Use: main | Type: host list* | Default: unset |
Some sites find it helpful to be able to limit the rate at which certain hosts can send them messages, and the rate at which an individual message can specify recipients.
Exim has two rate-limiting facilities. This section describes the older
facility, which can limit rates within a single connection. The newer
ratelimit
ACL condition can limit rates across all connections. See section
Rate limiting senders for details of the newer facility.
When a host matches smtp_ratelimit_hosts
, the values of
smtp_ratelimit_mail
and smtp_ratelimit_rcpt
are used to control the
rate of acceptance of MAIL and RCPT commands in a single SMTP session,
respectively. Each option, if set, must contain a set of four comma-separated
values:
For example, these settings have been used successfully at the site which first suggested this feature, for controlling mail from their customers:
smtp_ratelimit_mail = 2,0.5s,1.05,4m smtp_ratelimit_rcpt = 4,0.25s,1.015,4m |
The first setting specifies delays that are applied to MAIL commands after two have been received over a single connection. The initial delay is 0.5 seconds, increasing by a factor of 1.05 each time. The second setting applies delays to RCPT commands when more than four occur in a single message.
| Use: main | Type: string | Default: unset |
See smtp_ratelimit_hosts
above.
| Use: main | Type: string | Default: unset |
See smtp_ratelimit_hosts
above.
| Use: main | Type: time | Default: 5m |
This sets a timeout value for SMTP reception. It applies to all forms of SMTP input, including batch SMTP. If a line of input (either an SMTP command or a data line) is not received within this time, the SMTP connection is dropped and the message is abandoned. A line is written to the log containing one of the following messages:
SMTP command timeout on connection from... SMTP data timeout on connection from... |
The former means that Exim was expecting to read an SMTP command; the latter means that it was in the DATA phase, reading the contents of a message.
The value set by this option can be overridden by the
-os
command-line option. A setting of zero time disables the timeout, but
this should never be used for SMTP over TCP/IP. (It can be useful in some cases
of local input using -bs
or -bS
.) For non-SMTP input, the reception
timeout is controlled by receive_timeout
and -or
.
| Use: main | Type: host list* | Default: unset |
This option defines hosts for which SMTP connections are reserved; see
smtp_accept_reserve
and smtp_load_reserve
above.
| Use: main | Type: boolean | Default: false |
In the default state, Exim uses bland messages such as
"Administrative prohibition" when it rejects SMTP commands for policy
reasons. Many sysadmins like this because it gives away little information
to spammers. However, some other syadmins who are applying strict checking
policies want to give out much fuller information about failures. Setting
smtp_return_error_details
true causes Exim to be more forthcoming. For
example, instead of "Administrative prohibition", it might give:
550-Rejected after DATA: '>' missing at end of address: 550 failing address in "From" header is: <user@dom.ain |
| Use: main | Type: string | Default: see below |
This option is available when Exim is compiled with the content-scanning
extension. It specifies how Exim connects to SpamAssassin's spamd
daemon.
The default value is
127.0.0.1 783 |
See section Scanning with SpamAssassin for more details.
| Use: main | Type: boolean | Default: false |
If this option is set, it causes Exim to split its input directory into 62 subdirectories, each with a single alphanumeric character as its name. The sixth character of the message id is used to allocate messages to subdirectories; this is the least significant base-62 digit of the time of arrival of the message.
Splitting up the spool in this way may provide better performance on systems
where there are long mail queues, by reducing the number of files in any one
directory. The msglog directory is also split up in a similar way to the input
directory; however, if preserve_message_logs
is set, all old msglog files
are still placed in the single directory `msglog.OLD'.
It is not necessary to take any special action for existing messages when
changing split_spool_directory
. Exim notices messages that are in the
"wrong" place, and continues to process them. If the option is turned off
after a period of being on, the subdirectories will eventually empty and be
automatically deleted.
When split_spool_directory
is set, the behaviour of queue runner processes
changes. Instead of creating a list of all messages in the queue, and then
trying to deliver each one in turn, it constructs a list of those in one
sub-directory and tries to deliver them, before moving on to the next
sub-directory. The sub-directories are processed in a random order. This
spreads out the scanning of the input directories, and uses less memory. It is
particularly beneficial when there are lots of messages on the queue. However,
if queue_run_in_order
is set, none of this new processing happens. The
entire queue has to be scanned and sorted before any deliveries can start.
| Use: main | Type: string* | Default: set at compile time |
This defines the directory in which Exim keeps its spool, that is, the messages
it is waiting to deliver. The default value is taken from the compile-time
configuration setting, if there is one. If not, this option must be set. The
string is expanded, so it can contain, for example, a reference to
$primary_hostname
.
If the spool directory name is fixed on your installation, it is recommended
that you set it at build time rather than from this option, particularly if the
log files are being written to the spool directory (see log_file_path
).
Otherwise log files cannot be used for errors that are detected early on, such
as failures in the configuration file.
By using this option to override the compiled-in path, it is possible to run tests of Exim without using the standard spool.
| Use: main | Type: time | Default: 5s |
This option controls the timeout that the sqlite
lookup uses when trying to
access an SQLite database. See section More about SQLite for more details.
| Use: main | Type: boolean | Default: false |
If this option is set, redundant pairs of angle brackets round "route-addr" items in addresses are stripped. For example, <<xxx@a.b.c.d>> is treated as <xxx@a.b.c.d>. If this is in the envelope and the message is passed on to another MTA, the excess angle brackets are not passed on. If this option is not set, multiple pairs of angle brackets cause a syntax error.
| Use: main | Type: boolean | Default: false |
If this option is set, a trailing dot at the end of a domain in an address is ignored. If this is in the envelope and the message is passed on to another MTA, the dot is not passed on. If this option is not set, a dot at the end of a domain causes a syntax error. However, addresses in header lines are checked only when an ACL requests header syntax checking.
| Use: main | Type: boolean | Default: true |
When Exim is logging to syslog, it writes the log lines for its three
separate logs at different syslog priorities so that they can in principle
be separated on the logging hosts. Some installations do not require this
separation, and in those cases, the duplication of certain log lines is a
nuisance. If syslog_duplication
is set false, only one copy of any
particular log line is written to syslog. For lines that normally go to
both the main log and the reject log, the reject log version (possibly
containing message header lines) is written, at LOG_NOTICE priority.
Lines that normally go to both the main and the panic log are written at
the LOG_ALERT priority.
| Use: main | Type: string | Default: unset |
This option sets the syslog "facility" name, used when Exim is logging to syslog. The value must be one of the strings "mail", "user", "news", "uucp", "daemon", or "localx" where x is a digit between 0 and 7. If this option is unset, "mail" is used. See chapter Log files for details of Exim's logging.
| Use: main | Type: string | Default: `exim' |
This option sets the syslog "ident" name, used when Exim is logging to syslog. The value must be no longer than 32 characters. See chapter Log files for details of Exim's logging.
| Use: main | Type: boolean | Default: true |
If syslog_timestamp
is set false, the timestamps on Exim's log lines are
omitted when these lines are sent to syslog. See chapter Log files for
details of Exim's logging.
| Use: main | Type: string* | Default: unset |
This option specifies an Exim filter file that is applied to all messages at
the start of each delivery attempt, before any routing is done. System filters
must be Exim filters; they cannot be Sieve filters. If the system filter
generates any deliveries to files or pipes, or any new mail messages, the
appropriate system_filter_..._transport
option(s) must be set, to define
which transports are to be used. Details of this facility are given in chapter
System-wide message filtering.
| Use: main | Type: string* | Default: unset |
This sets the name of the transport driver that is to be used when the
save
command in a system message filter specifies a path ending in "/",
implying delivery of each message into a separate file in some directory.
During the delivery, the variable $address_file
contains the path name.
| Use: main | Type: string* | Default: unset |
This sets the name of the transport driver that is to be used when the save
command in a system message filter specifies a path not ending in "/". During
the delivery, the variable $address_file
contains the path name.
| Use: main | Type: string | Default: unset |
This option is used only when system_filter_user
is also set. It sets the
gid under which the system filter is run, overriding any gid that is associated
with the user. The value may be numerical or symbolic.
| Use: main | Type: string* | Default: unset |
This specifies the transport driver that is to be used when a pipe
command
is used in a system filter. During the delivery, the variable $address_pipe
contains the pipe command.
| Use: main | Type: string* | Default: unset |
This specifies the transport driver that is to be used when a mail
command
is used in a system filter.
| Use: main | Type: string | Default: unset |
If this option is not set, the system filter is run in the main Exim delivery
process, as root. When the option is set, the system filter runs in a separate
process, as the given user. Unless the string consists entirely of digits, it
is looked up in the password data. Failure to find the named user causes a
configuration error. The gid is either taken from the password data, or
specified by system_filter_group
. When the uid is specified numerically,
system_filter_group
is required to be set.
If the system filter generates any pipe, file, or reply deliveries, the uid
under which the filter is run is used when transporting them, unless a
transport option overrides. Normally you should set system_filter_user
if
your system filter generates these kinds of delivery.
| Use: main | Type: boolean | Default: true |
If this option is set false, it stops the Exim daemon setting the TCP_NODELAY option on its listening sockets. Setting TCP_NODELAY turns off the "Nagle algorithm", which is a way of improving network performance in interactive (character-by-character) situations. Turning it off should improve Exim's performance a bit, so that is what happens by default. However, it appears that some broken clients cannot cope, and time out. Hence this option. It affects only those sockets that are set up for listening by the daemon. Sockets created by the smtp transport for delivering mail always set TCP_NODELAY.
| Use: main | Type: time | Default: 0s |
If timeout_frozen_after
is set to a time greater than zero, a frozen
message of any kind that has been on the queue for longer than the given
time is automatically cancelled at the next queue run. If it is a bounce
message, it is just discarded; otherwise, a bounce is sent to the sender, in a
similar manner to cancellation by the -Mg
command line option. If you want
to timeout frozen bounce messages earlier than other kinds of frozen message,
see ignore_bounce_errors_after
.
| Use: main | Type: string | Default: unset |
The value of timezone
is used to set the environment variable TZ while
running Exim (if it is different on entry). This ensures that all timestamps
created by Exim are in the required timezone. If you want all your timestamps
to be in UTC (aka GMT) you should set
timezone = UTC |
The default value is taken from TIMEZONE_DEFAULT in `Local/Makefile',
or, if that is not set, from the value of the TZ environment variable when Exim
is built. If timezone
is set to the empty string, either at build or run
time, any existing TZ variable is removed from the environment when Exim
runs. This is appropriate behaviour for obtaining wall-clock time on some, but
unfortunately not all, operating systems.
| Use: main | Type: host list* | Default: unset |
When Exim is built with support for TLS encrypted connections, the availability of the STARTTLS command to set up an encrypted session is advertised in response to EHLO only to those client hosts that match this option. See chapter Encrypted SMTP connections using TLS/SSL for details of Exim's support for TLS.
| Use: main | Type: string* | Default: unset |
The value of this option is expanded, and must then be the absolute path to a
file which contains the server's certificates. The server's private key is also
assumed to be in this file if tls_privatekey
is unset. See chapter
Encrypted SMTP connections using TLS/SSL for further details.
Note: The certificates defined by this option are used only when Exim is
receiving incoming messages as a server. If you want to supply certificates for
use when sending messages as a client, you must set the tls_certificate
option in the relevant smtp
transport.
| Use: main | Type: string* | Default: unset |
This option specifies a certificate revocation list. The expanded value must be the name of a file that contains a CRL in PEM format.
| Use: main | Type: string* | Default: unset |
The value of this option is expanded, and must then be the absolute path to a file which contains the server's DH parameter values. This is used only for OpenSSL. When Exim is linked with GnuTLS, this option is ignored. See section OpenSSL vs GnuTLS for further details.
| Use: main | Type: string list | Default: unset |
This option specifies a list of incoming SSMTP (aka SMTPS) ports that should operate the obsolete SSMTP (SMTPS) protocol, where a TLS session is immediately set up without waiting for the client to issue a STARTTLS command. For further details, see section Support for the obsolete SSMTP (or SMTPS) protocol.
| Use: main | Type: string* | Default: unset |
The value of this option is expanded, and must then be the absolute path to a file which contains the server's private key. If this option is unset, or if the expansion is forced to fail, or the result is an empty string, the private key is assumed to be in the same file as the server's certificates. See chapter Encrypted SMTP connections using TLS/SSL for further details.
| Use: main | Type: boolean | Default: false |
If this option is set true, Exim violates the RFCs by remembering that it is in "esmtp" state after successfully negotiating a TLS session. This provides support for broken clients that fail to send a new EHLO after starting a TLS session.
| Use: main | Type: string* | Default: unset |
This option controls which ciphers can be used for incoming TLS connections.
The smtp
transport has an option of the same name for controlling outgoing
connections. This option is expanded for each connection, so can be varied for
different clients if required. The value of this option must be a list of
permitted cipher suites. The OpenSSL and GnuTLS libraries handle cipher control
in somewhat different ways. If GnuTLS is being used, the client controls the
preference order of the available ciphers. Details are given in sections
Requiring specific ciphers in OpenSSL and Requiring specific ciphers in GnuTLS.
| Use: main | Type: host list* | Default: unset |
See tls_verify_hosts
below.
| Use: main | Type: string* | Default: unset |
The value of this option is expanded, and must then be the absolute path to
a file containing permitted certificates for clients that
match tls_verify_hosts
or tls_try_verify_hosts
. Alternatively, if you
are using OpenSSL, you can set tls_verify_certificates
to the name of a
directory containing certificate files. This does not work with GnuTLS; the
option must be set to the name of a single file if you are using GnuTLS.
| Use: main | Type: host list* | Default: unset |
This option, along with tls_try_verify_hosts
, controls the checking of
certificates from clients.
The expected certificates are defined by tls_verify_certificates
, which
must be set. A configuration error occurs if either tls_verify_hosts
or
tls_try_verify_hosts
is set and tls_verify_certificates
is not set.
Any client that matches tls_verify_hosts
is constrained by
tls_verify_certificates
. The client must present one of the listed
certificates. If it does not, the connection is aborted.
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
certificate and checks it against tls_verify_certificates
, but does not
abort the connection if there is no certificate or if it does not match. This
state can be detected in an ACL, which makes it possible to implement policies
such as "accept for relay only if a verified certificate has been received,
but accept for local delivery if encrypted, even without a verified
certificate".
Client hosts that match neither of these lists are not asked to present certificates.
| Use: main | Type: string list* | Default: unset |
This option is expanded just once, at the start of Exim's processing. If this
option is set, any process that is running in one of the listed groups, or
which has one of them as a supplementary group, is trusted. The groups can be
specified numerically or by name. See section Trusted and admin users for
details of what trusted callers are permitted to do. If neither
trusted_groups
nor trusted_users
is set, only root and the Exim user
are trusted.
| Use: main | Type: string list* | Default: unset |
This option is expanded just once, at the start of Exim's processing. If this
option is set, any process that is running as one of the listed users is
trusted. The users can be specified numerically or by name. See section
Trusted and admin users for details of what trusted callers are permitted to do.
If neither trusted_groups
nor trusted_users
is set, only root and the
Exim user are trusted.
| Use: main | Type: string* | Default: unset |
This is a specialized feature for use in unusual configurations. By default, if
the uid of the caller of Exim cannot be looked up using getpwuid()
, Exim
gives up. The unknown_login
option can be used to set a login name to be
used in this circumstance. It is expanded, so values like user$caller_uid
can be set. When unknown_login
is used, the value of unknown_username
is used for the user's real name (gecos field), unless this has been set by the
-F
option.
| Use: main | Type: string | Default: unset |
See unknown_login
.
| Use: main | Type: address list* | Default: unset |
When an untrusted user submits a message to Exim using the standard input, Exim
normally creates an envelope sender address from the user's login and the
default qualification domain. Data from the -f
option (for setting envelope
senders on non-SMTP messages) or the SMTP MAIL command (if -bs
or -bS
is used) is ignored.
However, untrusted users are permitted to set an empty envelope sender address, to declare that a message should never generate any bounces. For example:
exim -f '<>' user@domain.example |
The untrusted_set_sender
option allows you to permit untrusted users to set
other envelope sender addresses in a controlled way. When it is set, untrusted
users are allowed to set envelope sender addresses that match any of the
patterns in the list. Like all address lists, the string is expanded. The
identity of the user is in $sender_ident
, so you can, for example, restrict
users to setting senders that start with their login ids
followed by a hyphen
by a setting like this:
untrusted_set_sender = ^$sender_ident- |
If you want to allow untrusted users to set envelope sender addresses without restriction, you can use
untrusted_set_sender = * |
The untrusted_set_sender
option applies to all forms of local input, but
only to the setting of the envelope sender. It does not permit untrusted users
to use the other options which trusted user can use to override message
parameters. Furthermore, it does not stop Exim from removing an existing
Sender: header in the message, or from adding a Sender: header if
necessary. See local_sender_retain
and local_from_check
for ways of
overriding these actions. The handling of the Sender: header is also
described in section The Sender: header line.
The log line for a message's arrival shows the envelope sender following
"<=". For local messages, the user's login always follows, after "U=". In
-bp
displays, and in the Exim monitor, if an untrusted user sets an
envelope sender address, the user's login is shown in parentheses after the
sender address.
| Use: main | Type: string | Default: see below |
Some applications that pass messages to an MTA via a command line interface use
an initial line starting with "From " to pass the envelope sender. In
particular, this is used by UUCP software. Exim recognizes such a line by means
of a regular expression that is set in uucp_from_pattern
. When the pattern
matches, the sender address is constructed by expanding the contents of
uucp_from_sender
, provided that the caller of Exim is a trusted user. The
default pattern recognizes lines in the following two forms:
From ph10 Fri Jan 5 12:35 GMT 1996 From ph10 Fri, 7 Jan 97 14:00:00 GMT |
The pattern can be seen by running
exim -bP uucp_from_pattern |
It checks only up to the hours and minutes, and allows for a 2-digit or 4-digit
year in the second case. The first word after "From " is matched in the
regular expression by a parenthesized subpattern. The default value for
uucp_from_sender
is "$1", which therefore just uses this first word
("ph10" in the example above) as the message's sender. See also
ignore_fromline_hosts
.
| Use: main | Type: string* | Default: `$1' |
See uucp_from_pattern
above.
| Use: main | Type: string | Default: unset |
This option defines a template file containing paragraphs of text to be used
for constructing the warning message which is sent by Exim when a message has
been on the queue for a specified amount of time, as specified by
delay_warning
. Details of the file's contents are given in chapter
Customizing bounce and warning messages. See also bounce_message_file
.
| Use: main | Type: boolean | Default: true |
If this option is set false, Exim no longer writes anything to the reject log. See chapter Log files for details of what Exim writes to its logs.
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