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Exim Filter Specification - Testing a new filter file Go to the first, previous, next, last section, table of contents.

1.2 Testing a new filter file

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' Exim Overview
The Exim Mail Transport Agent
Table of Contents Exim Overview Background Availability Limitations Main features Performance Interface Method of operation Mail filtering Directors Routers Transports Exim logs Exim databases SMTP batching Retries Header rewriting Host verification SMTP port reservation Control of relaying Sender verification Sender lock out Receiver verification The `percent hack' Security The Exim Monitor Exim Overview 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 334679 University 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) Background 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. Availability 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. Limitations For the benefit of those reading this overview to see whether Exim is of interest to them, its limitations are listed first. Exim is written in ANSI C. This should not be much of a limitation these days. However, to help with systems that lack a true ANSI C library, Exim avoids making any use of the value returned by the `sprintf()' function, which is one of the main incompatibilities. It has its own version of `strerror()' for use with SunOS4 and any other system that lacks this function, and a macro can be defined to turn `memmove()' into `bcopy()' if necessary. Exim uses file names that are longer than 14 characters. Exim is intended for use as an Internet mailer, and therefore handles addresses in RFC 822 domain format only. It cannot handle `bang paths', though simple two-component bang paths can be converted by a straightforward rewriting configuration. Exim insists that every address it handles has a domain attached. For incoming local messages, domainless addresses are automatically qualified with a configured domain value. Configuration options specify from which remote systems unqualified addresses are acceptable. The only external transport currently implemented is an SMTP transport over a TCP/IP network (using sockets), suitable for machines on the Internet. However, a pipe transport is available, and there are facilities for writing messages to files in `batched SMTP' format; both of these can be used to send messages to some other transport mechanism such as UUCP. Batched SMTP input is also catered for. Main features 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 configuration options can be given as expansion strings, and as these can include file lookups, much of Exim's operation can be made table-driven if desired. For example, it is possible to do local delivery on a machine on which the users do not have accounts. Regular expressions are available i Exim 4.00 Specification chapter 11 Previous Next Contents (Exim 4.00 Specification) 11. String expansions 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. 11.1. Literal text in expanded strings 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. 11.2. Character escape sequences in expanded strings 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. 11.3. Testing string expansions 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. 11.4. Expansion items 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 ${ Exim 4.00 Specification chapter 13 Previous Next Contents (Exim 4.00 Specification) 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. accept_8bitmime 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. acl_smtp_auth Type: string, expanded Default: unset This option defines the ACL that is run when an SMTP AUTH command is received. See chapter 37 for further details. acl_smtp_data Type: string, expanded 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 37 for further details. acl_smtp_etrn Type: string, expanded Default: unset This option defines the ACL that is run when an SMTP ETRN command is received. See chapter 37 for further details. acl_smtp_expn Type: string, expanded Default: unset This option defines the ACL that is run when an SMTP EXPN command is received. See chapter 37 for further details. acl_smtp_rcpt Type: string, expanded Default: unset This option defines the ACL that is run when an SMTP RCPT command is received. See chapter 37 for further details. acl_smtp_vrfy Type: string, expanded Default: unset This option defines the ACL that is run when an SMTP VRFY command is received. See chapter 37 for further details. admin_groups Type: string Default: unset 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. allow_domain_literals 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. allow_mx_to_ip 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. auth_advertise_hosts Type: host list, expanded 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, 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. auto_thaw 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 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. bi_command 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 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. bounce_message_file 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 40. See also warn_message_file. bounce_message_text 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. bounce_return_message Type: boolean Default: true If this option is set false, the original message is not included in bounce messages generated by Exim. See also return_size_limit. bounce_sender_authentication 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. check_log_inodes Type: integer Default: 0 See check_spool_space below. check_log_space Type: integer Default: 0 See check_spool_space below. check_spool_inodes Type: integer Default: 0 See check_spool_space below. check_spool_space Type: integer Default: 0 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. daemon_smtp_port Type: string Default: unset 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. delay_warning Type: time list Default: 24h 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. delay_warning_condition Type: string, expanded 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 = \ ${if match{$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. deliver_drop_privilege 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 47. deliver_queue_load_max 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. delivery_date_remove 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. dns_again_means_nonexist Type: domain list, expanded 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. dns_check_names_pattern Type: string Default: see below 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. dns_ipv4_lookup Type: domain list, expanded Default: unset 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. dns_retrans 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. dns_retry Type: integer Default: 0 See dns_retrans above. drop_cr Type: boolean Default: false 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. envelope_to_remove 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. errors_copy Type: string list, expanded 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 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, $1, etc. are set in the normal way. errors_reply_to Type: string Default: unset Exim's bounce messages contain the header line From: Mail Delivery System <Mailer-Daemon@$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. exim_group 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 47 for a discussion of security issues. exim_path 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 Exim is run from some other place. exim_user 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 47 for a discussion of security issues. extract_addresses_remove_arguments 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. finduser_retries 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. freeze_tell Type: string Default: unset 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. gecos_name Type: string, expanded 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 gecos_pattern Type: string Default: unset See gecos_name above. helo_accept_junk_hosts Type: host list, expanded 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. helo_lookup_domains Type: domain list, expanded 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. helo_try_verify_hosts Type: host list, expanded Default: unset See helo_verify_hosts below. helo_verify_hosts Type: host list, expanded Default: unset 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. hold_domains Type: domain list, expanded 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. host_lookup Type: host list, expanded 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 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. host_reject_connection Type: host list, expanded 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 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. hosts_treat_as_local Type: domain list, expanded 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. 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). ignore_bounce_errors_after Type: time Default: 10w 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. ignore_fromline_hosts Type: host list, expanded 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. ignore_fromline_local Type: boolean Default: false See ignore_fromline_hosts above. keep_malformed 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. ldap_default_servers 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 9.10 for details of LDAP queries. This option is available only when Exim has been built with LDAP support. local_from_check 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. 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. local_from_prefix 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 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. local_from_suffix Type: string Default: unset See local_from_prefix above. local_interfaces Type: string list Default: unset 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 liste

The Exim Mail Transport Agent

Table of Contents

accept_8bitmime

acl_smtp_auth

acl_smtp_data

acl_smtp_etrn

acl_smtp_expn

acl_smtp_rcpt

acl_smtp_vrfy

admin_groups

allow_domain_literals

allow_mx_to_ip

auth_advertise_hosts

auto_thaw

bi_command

bounce_message_file

bounce_message_text

bounce_return_message

bounce_sender_authentication

check_log_inodes

check_log_space

check_spool_inodes

check_spool_space

daemon_smtp_port

delay_warning

delay_warning_condition

deliver_drop_privilege

deliver_queue_load_max

delivery_date_remove

dns_again_means_nonexist

dns_check_names_pattern

dns_ipv4_lookup

dns_retrans

dns_retry

drop_cr

envelope_to_remove

errors_copy

errors_reply_to

exim_group

exim_path

exim_user

extract_addresses_remove_arguments

finduser_retries

freeze_tell

gecos_name

gecos_pattern

helo_accept_junk_hosts

helo_lookup_domains

helo_try_verify_hosts

helo_verify_hosts

hold_domains

host_lookup

host_reject_connection

hosts_treat_as_local

ignore_bounce_errors_after

ignore_fromline_hosts

ignore_fromline_local

keep_malformed

ldap_default_servers

local_from_check

local_from_prefix

local_from_suffix

local_interfaces

`The Exim Mail Transport Agent`