Filter files, especially the more complicated ones, should always be tested, as
it is easy to make mistakes. Exim provides a facility for preliminary testing
of a filter file before installing it. This tests the syntax of the file and
its basic operation, and can also be used with ordinary `.forward'
The Exim Mail Transport Agent
Date: 10 July 1997
Exim is a mail transport agent (MTA) developed at the University of Cambridge for use on Unix systems connected to the Internet. It is freely available under the terms of the GNU General Public Licence. In style it is similar to Smail 3, but its facilities are more extensive, and in particular it has some defences against mail bombs and unsolicited junk mail, in the form of options for refusing messages from particular hosts, networks, or senders.
Exim is in production use on a number of sites that move tens of thousands of messages per day. This document contains an overview description of the way Exim works, with a certain amount of omission and simplification to keep it fairly short. Please address any enquiries about Exim to Philip Hazel:
Email: <ph10@cus.cam.ac.uk> Phone: +44 1223 334714 Fax: +44 1223 334679University of Cambridge Computer Laboratory Pembroke Street Cambridge CB2 3QG United Kingdom
This document is copyright (c) University of Cambridge 1997, but copying
permission is granted to all.
-------------------------------------------------------------------------
"If I have seen further it is by standing on the shoulders of giants."
(Isaac Newton)
Exim owes a great deal to Smail 3 and its author, Ron Karr. Without the experience of running and working on the Smail 3 code, I could never have contemplated starting to write a new mailer. Many of the ideas and configuration interfaces are taken from Smail 3, though the actual code of Exim is entirely new.
My intention was to write a mailer that had more functionality than Smail 3, but which retained the simple lightweight approach, as this seemed to me to be all that was needed for systems directly connected to the Internet, where most messages are delivered almost immediately.
The current distribution of Exim is available from
$st{ftp://ftp.cus.cam.ac.uk/pub/software/programs/exim/exim-$si{n.nn}.tar.gz}
where n.nn is the version number. The distribution contains an ASCII copy of the documentation; other formats are available from
$st{ftp://ftp.cus.cam.ac.uk/pub/software/programs/exim/exim-postscript-$si{n.nn}.tar.gz}
$st{ftp://ftp.cus.cam.ac.uk/pub/software/programs/exim/exim-texinfo-$si{n.nn}.tar.gz}
The following operating systems are currently supported: AIX, BSDI, DGUX, FreeBSD, HI-OSF (Hitachi), HP-UX, IRIX, Linux, MIPS RISCOS, NetBSD, OpenBSD, DEC OSF1 (aka Digital UNIX), SCO, SCO SVR4.2 (aka UNIX-SV), SunOS4, SunOS5, Ultrix, and Unixware.
For the benefit of those reading this overview to see whether Exim is of interest to them, its limitations are listed first.
Exim follows the same general approach of decentralized control that Smail 3 does. There is no central process doing overall management of mail delivery. However, unlike Smail, the independent delivery processes share data in the form of `hints', which makes delivery more efficient in some cases. The hints are kept in a number of DBM files. If any of these files are lost, the only effect is to change the pattern of delivery attempts and retries.
Here is a summary of Exim's main features. More details are given in the sections which follow.
Many strings that are given in Exim's run time configuration are expanded before use. Some of them are expanded every time they are used; others are expanded only once.
When a string is being expanded it is copied verbatim from left to right except when a dollar or backslash character is encountered. A dollar specifies the start of a portion of the string which is interpreted and replaced as described below in section 11.4 onwards.
An uninterpreted dollar can be included in an expanded string by putting a backslash in front of it. A backslash can be used to prevent any special character being treated specially in an expansion, including itself. If the string appears in quotes in the configuration file, two backslashes are required because the quotes themselves cause interpretation of backslashes when the string is read in.
An entire portion of the string can specified as non-expandable by placing it between two occurrences of \N. This is particularly useful for protecting regular expressions, which often contain backslashes and dollar signs. For example:
deny senders = \N^\d{8}[a-z]@some\.site\.example$\N
On encountering the first \N, the expander copies subsequent characters without interpretation until it reaches the next \N or the end of the string.
A backslash followed by one of the letters ``n'', ``r'', or ``t'' in an expanded string is recognized as an escape sequence for the character newline, carriage return, or tab, respectively. A backslash followed by up to three octal digits is recognized as an octal encoding for a single character, and a backslash followed by ``x'' and up to two hexadecimal digits is a hexadecimal encoding.
These escape sequences are also recognized in quoted strings when they are read in. Their interpretation in expansions as well is useful for unquoted strings, and for other cases such as looked-up strings that are then expanded.
Many expansions can be tested by calling Exim with the -be option. This takes the command arguments, or lines from the standard input if there are no arguments, runs them through the string expansion code, and writes the results to the standard output. Variables based on configuration values are set up, but since no message is being processed, variables such as $local_part have no value. Nevertheless the -be option can be useful for checking out file and database lookups, and the use of expansion operators such as substr and hash.
Exim gives up its root privilege when it is called with the -be option, and instead runs under the uid and gid it was called with, to prevent users from using -be for reading files to which they normally do not have access.
The following items are recognized in expanded strings. White space may be used between sub-items that are keywords or substrings enclosed in braces inside an outer set of braces, to improve readability. Within braces, however, white space is significant.
$<variable name> or ${
13. Main configuration
The first part of the run time configuration file contains three types of item:
Macro definitions: These lines start with an upper case letter. See section 6.4 for details of macro processing.
Named list definitions: These lines start with one of the words ``domainlist'', ``hostlist'', ``addresslist'', or ``localpartlist''. Their use is described in section 10.5.
Main configuration settings: Each setting occupies one line of the file (including possible continuations). If any setting is preceded by the word ``hide'', the -bP option displays its value to admin users only (see section 6.5).
This chapter lists all the main configuration options, along with their types and default values, in alphabetical order.
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.
This option defines the ACL that is run when an SMTP AUTH command is received. See chapter 37 for further details.
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 37 for further details.
This option defines the ACL that is run when an SMTP ETRN command is received. See chapter 37 for further details.
This option defines the ACL that is run when an SMTP EXPN command is received. See chapter 37 for further details.
This option defines the ACL that is run when an SMTP RCPT command is received. See chapter 37 for further details.
This option defines the ACL that is run when an SMTP VRFY command is received. See chapter 37 for further details.
If the current group or any of the supplementary groups of the 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.
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.
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.
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, though it is always prepared to accept it.
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 this option is set to a time greater than zero, a queue runner will try a new delivery attempt on any frozen 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''. See also timeout_frozen_after and ignore_bounce_errors_after.
This option supplies the name of a command that is run when Exim is called with the -bi option (see chapter 5). 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.
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 40. See also warn_message_file.
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.
If this option is set false, the original message is not included in bounce messages generated by Exim. See also return_size_limit.
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.
See check_spool_space below.
See check_spool_space below.
See check_spool_space below.
The four check_... options allow for checking of disc resources before a message is accepted: 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 which 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.
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.
This option specifies the default SMTP port on which the Exim daemon listens. It can either be given as a number, or as a service name. It can be overridden by giving an explicit port number on an IP address in the local_interfaces option, or by using -oX on the command line. If this option is not set, the service name ``smtp'' is used.
When a message is delayed, Exim sends a warning message to the sender at intervals specified by this option. If it is set to a zero, no warnings are sent. The data is a colon-separated list of times after which to send warning messages. 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 subsequent ones every 16 hours thereafter. To stop warnings after a given time, set a huge subsequent time.
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 = \
${if match{$h_precedence:}{(?i)bulk|list|junk}{no}{yes}}
which suppresses the sending of warnings about messages that have ``bulk'', ``list'' or ``junk'' in a Precedence: header.
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 47.
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.
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.
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.
When this option is set to a non-empty string, it causes Exim to check domain names for illegal characters before handing them to the DNS resolver, because some resolvers give temporary errors for malformed names. If a domain name contains any illegal 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, and hyphens in components, but they may not start or end with a hyphen.
When Exim is compiled with IPv6 support, it looks for IPv6 address records (AAAA and, if configured, A6) as well as IPv4 address 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 new IPv6 record types. If Exim is handed an IPv6 address record as a result of an MX lookup, it always recognizes it, and may as a result make an outgoing IPv6 connection. All this option does is to make Exim look only for IPv4-style A records when it needs to find an IP address for a host name. In due course, when the world's name servers have all been upgraded, there should be no need for this option.
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.
See dns_retrans above.
Setting drop_cr true affects non-SMTP messages that are submitted locally. It causes every carriage return character that immediately precedes a linefeed to be discarded. Other carriage returns are treated as data. This action can be requested for individual messages by means of the -dropcr command line option.
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.
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 10.12). 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, $1, etc. are set in the normal way.
Exim's bounce messages contain the header line
From: Mail Delivery System <Mailer-Daemon@$qualify_domain>
(suitably expanded). Experience shows that a large number of people reply to bounce messages. If the errors_reply_to option is set, a Reply-To: header is added. The option must specify the complete header body.
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 47 for a discussion of security issues.
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 Exim is run from some other place.
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 47 for a discussion of security issues.
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.
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.
On encountering certain errors, or when configured to do so in a system filter, Exim freezes a message. This means that no further delivery attempts take place until an administrator (or the auto_thaw feature) thaws the message. If freeze_tell is set, Exim generates a warning message whenever it freezes something, unless the message it is freezing is a 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. The reason(s) for freezing can be found in the message log.
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
See gecos_name above.
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.
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.
See helo_verify_hosts below.
The RFCs mandate that a server must not reject a message because it doesn't like the HELO or EHLO command. By default, Exim just checks the syntax of these commands (see helo_accept_junk_hosts above). However, some sites like to be stricter. If helo_verify_hosts or helo_try_verify_hosts is set, Exim refuses to accept messages from hosts that match either of them, unless a HELO or EHLO command is received before the MAIL command. Otherwise, MAIL commands are rejected with a 550 error. Furthermore, Exim checks that the host name given in the HELO or EHLO command either:
is an IP literal matching the calling address of the host (the RFCs specifically allow this), or
matches the host name that Exim obtains by doing a reverse lookup of the calling host address, or
when looked up using gethostbyname() yields the calling host address.
The difference between helo_verify_hosts and helo_try_verify_hosts is in what happens if these conditions are not met. For hosts that match the former option, the HELO or EHLO command is rejected with a 550 error, and entries are written to the main and reject logs. For the latter option, processing continues. This state can be detected in an ACL, allowing it to be used to accept or reject addresses in conjunction with other options.
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.
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 helo_verify_hosts is set, or the address 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. See also helo_lookup_domains.
If this option is set, incoming SMTP calls from the hosts listed are rejected as soon as the connection is made. This option is provided for use in unusual cases. Many host will just try again. Normally, it is better to use an ACL to reject incoming messages at a later stage, such as after RCPT commands. See chapter 37.
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. This option also applies when Exim is matching the special items @mx_any, @mx_primary, and @mx_secondary in a domain list (see section 10.6), and when checking the host option in the smtp transport for the local host (see the allow_localhost option in that transport).
This option affects the processing of bounce messages that cannot be delivered. After an initial failure, such 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.
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.
See ignore_fromline_hosts above.
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.
This option provides a list of LDAP servers which are tried in turn when an LDAP query does not contain a server. See section 9.10 for details of LDAP queries. This option is available only when Exim has been built with LDAP support.
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. 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. Section 43.12 has more details about Sender: processing.
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 14). 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.
See local_from_prefix above.
The string must contain a list of IP addresses, in dotted-quad format for IPv4 addresses, or in colon-separated format for IPv6 addresses. It is usually easier to change the list separator character instead of doubling all the colons in IPv6 addresses. For example:
local_interfaces = <; 127.0.0.1 ; \ 192.168.23.65 ; \ ::1 ; \ 3ffe:ffff:836f::fe86:a061
A port number can be specified along with each IP address. Two different formats are recognized:
The port is added onto the address with a dot separator, for example,
local_interfaces = <; 192.168.23.65.1234 ; \ 3ffe:ffff:836f::fe86:a061.1234
The IP address is enclosed in square brackets, and the port is added with a colon separator, for example,
local_interfaces = <; [192.168.23.65]:1234 ; \ [3ffe:ffff:836f::fe86:a061]:1234
This list of IP addresses is used for two different purposes:
When a daemon is started to listen for incoming SMTP calls, it listens only on the interfaces and ports identified here. For interfaces listed without a port, the value of daemon_smtp_port is used, unless overridden by the -oX option. Exim can be made to listen on more than one port by listing the same interface with different port numbers, for example:
local_interfaces = 192.168.34.67.25 : 192.168.34.67.26
When a message is received over TCP/IP, the interface and port that were used are set in $interface_address and $interface_port. When the daemon is started, an error occurs if it is unable to bind a listening socket to any listed interface.
Only the IP addresses listed here are taken as the local host's IP addresses when routing mail and checking for mail loops. In this case, the port values are not used.
If local_interfaces is unset, the daemon issues a generic listen() that accepts incoming calls to any interface. The same port is used in all cases. In addition, Exim gets a complete list of available interfaces from the operating system, and treats them all as local when routing mail. On most systems, the default action is what is wanted. However, some systems set up large numbers of virtual interfaces in order to provide many different virtual web servers. In these cases local_interfaces can be used to restrict SMTP traffic to one or two interfaces only. See also hosts_treat_as_local.
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). Section 43.12 has more details about Sender: processing.
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 0-255. This is available in subsequent string expansions via the variable $localhost_number. The final two characters of the message id, instead of just being a sequence count of the number of messages received by one process in one second, are the base 62 encoding of
<sequence count> * 256 + <local host number>
This reduces the possible range of the sequence count to 0-14. If the count ever reaches 14 in a receiving process, a delay of one second is imposed to allow the clock to tick, thereby allowing the count to be reset to zero.
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, they are written in a sub-directory called log in Exim's spool directory. Chapter 44 contains further details about Exim's logging, and section 44.1 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.
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 44.13.
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.
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.
This option specifies how much of a message's body is to be included in the $message_body and $message_body_end expansion variables.
If this variable is set, the string is expanded and used to augment the text of the Message-id: header that Exim creates if an 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 does not yield an empty string, it 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.
This option limits the maximum size of message that Exim will process. The value is expanded for each incoming message so, for example, it can be made to depend on the IP address of the remote host for messages arriving via TCP/IP. String expansion failure causes a temporary error. A value of zero means no limit, but its use is not recommended. See also 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.
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.
This option provides a list of MySQL servers and associated connection data, to be used in conjunction with mysql lookups (see section 9.14). The option is available only if Exim has been built with MySQL support.
Local mail 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. If a message is to be delivered as one of the users on the never_users list, an error occurs, and delivery is deferred. A common example is
never_users = root:daemon:bin
This option overrides the pipe_as_creator option of the pipe transport driver.
This option provides a list of Oracle servers and associated connection data, to be used in conjunction with oracle lookups (see section 9.14). The option is available only if Exim has been built with Oracle support.
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.
This option is available only when Exim is built with an embedded Perl interpreter. See chapter 12 for details of its use.
This option is available only when Exim is built with an embedded Perl interpreter. See chapter 12 for details of its use.
This option provides a list of PostgreSQL servers and associated connection data, to be used in conjunction with pgsql lookups (see section 9.14). The option is available only if Exim has been built with PostgreSQL support.
This option sets the path which is used to determine 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.
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!
This specifies the name of the current host. This is used in the EHLO command for outgoing SMTP messages, and as the default for qualify_domain. If it is not set, Exim calls uname() to find it. If this fails, Exim panics and dies. If the name returned by uname() contains only one component, Exim passes it to gethostbyname() in order to obtain the fully qualified version.
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.
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.
This option specifies the domain name that is added to any sender addresses that do not have a domain qualification. It also applies to recipient addresses if qualify_recipient is not set. Such addresses are accepted by default only for locally-generated messages. Messages from external sources must always contain fully qualified addresses, unless the sending host matches recipient_unqualified_hosts or sender_unqualified_hosts (as appropriate). If qualify_domain is not set, it defaults to the primary_hostname value.
This specifies the domain name that is added to any recipient addresses that do not have a domain qualification. Such addresses are accepted by default only for locally-generated messages. Messages from external sources must always contain fully qualified recipient addresses, unless the sending host matches recipient_unqualified_hosts. If qualify_recipient is not set, it defaults to the qualify_domain value.
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.
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.
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. The -odq command line has the same effect. Even if queue_only is false, incoming messages may not get delivered immediately when certain conditions occur. See queue_only_file, queue_only_load and smtp_accept_queue.
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.
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.
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 in a single directory (the default), this happens anyway, but if split_spool_directory is set it does not - for delivery in random order, the sub-directories are processed one at a time (in random order), to avoid setting up one huge list. Thus, setting queue_run_in_order with split_spool_directory may degrade performance when the queue is large. In most situations, queue_run_in_order should not be set.
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.
When this
Exim's command line takes the standard Unix form of a sequence of options, each starting with a hyphen character, followed by a number of arguments. The options are compatible with the main options of Sendmail, and there are also some additional options, some of which are compatible with Smail 3. Certain combinations of options do not make sense, and provoke an error if used. The form of the arguments depends on which options are set.
If Exim is called under the name mailq, it behaves as if the option -bp were present before any other options. This is for compatibility with some systems that contain a command of that name in one of the standard libraries, symbolically linked to /usr/sbin/sendmail or /usr/lib/sendmail.
If Exim is called under the name rsmtp it behaves as if the option -bS were present before any other options, for compatibility with Smail. The -bS option is used for reading in a number of messages in batched SMTP format.
If Exim is called under the name rmail it behaves as if the -i and -oee options were present before any other options, for compatibility with Smail. The name rmail is used as an interface by some UUCP systems.
If Exim is called under the name runq it behaves as if the option -q were present before any other options, for compatibility with Smail. The -q option causes a single queue-runner process to be started.
If Exim is called under the name newaliases it behaves as if the option -bi were present before any other options, for compatibility with Sendmail. This option is used for rebuilding Sendmail's alias file. Exim does not have the concept of a single alias file, but can be configured to run a given command if called with the -bi option.
Some Exim options are available only to trusted users and others are available only to admin users. In the description below, the phrases ``Exim user'' and ``Exim group'' mean the user and group defined by EXIM_USER and EXIM_GROUP in Local/Makefile or set by the exim_user and exim_group options. These do not necess