1 From time to time, experimental features may be added to Exim.
2 While a feature is experimental, there will be a build-time
3 option whose name starts "EXPERIMENTAL_" that must be set in
4 order to include the feature. This file contains information
5 about experimental features, all of which are unstable and
6 liable to incompatible change.
9 Brightmail AntiSpam (BMI) support
10 --------------------------------------------------------------
12 Brightmail AntiSpam is a commercial package. Please see
13 http://www.brightmail.com for more information on
14 the product. For the sake of clarity, we'll refer to it as
18 0) BMI concept and implementation overview
20 In contrast to how spam-scanning with SpamAssassin is
21 implemented in exiscan-acl, BMI is more suited for per
22 -recipient scanning of messages. However, each messages is
23 scanned only once, but multiple "verdicts" for multiple
24 recipients can be returned from the BMI server. The exiscan
25 implementation passes the message to the BMI server just
26 before accepting it. It then adds the retrieved verdicts to
27 the messages header file in the spool. These verdicts can then
28 be queried in routers, where operation is per-recipient
29 instead of per-message. To use BMI, you need to take the
32 1) Compile Exim with BMI support
33 2) Set up main BMI options (top section of Exim config file)
34 3) Set up ACL control statement (ACL section of the config
36 4) Set up your routers to use BMI verdicts (routers section
38 5) (Optional) Set up per-recipient opt-in information.
40 These four steps are explained in more details below.
42 1) Adding support for BMI at compile time
44 To compile with BMI support, you need to link Exim against
45 the Brightmail client SDK, consisting of a library
46 (libbmiclient_single.so) and a header file (bmi_api.h).
47 You'll also need to explicitly set a flag in the Makefile to
48 include BMI support in the Exim binary. Both can be achieved
49 with these lines in Local/Makefile:
51 EXPERIMENTAL_BRIGHTMAIL=yes
52 CFLAGS=-I/path/to/the/dir/with/the/includefile
53 EXTRALIBS_EXIM=-L/path/to/the/dir/with/the/library -lbmiclient_single
55 If you use other CFLAGS or EXTRALIBS_EXIM settings then
56 merge the content of these lines with them.
58 Note for BMI6.x users: You'll also have to add -lxml2_single
59 to the EXTRALIBS_EXIM line. Users of 5.5x do not need to do
62 You should also include the location of
63 libbmiclient_single.so in your dynamic linker configuration
64 file (usually /etc/ld.so.conf) and run "ldconfig"
65 afterwards, or else the produced Exim binary will not be
66 able to find the library file.
69 2) Setting up BMI support in the Exim main configuration
71 To enable BMI support in the main Exim configuration, you
72 should set the path to the main BMI configuration file with
73 the "bmi_config_file" option, like this:
75 bmi_config_file = /opt/brightmail/etc/brightmail.cfg
77 This must go into section 1 of Exim's configuration file (You
78 can put it right on top). If you omit this option, it
79 defaults to /opt/brightmail/etc/brightmail.cfg.
81 Note for BMI6.x users: This file is in XML format in V6.xx
82 and its name is /opt/brightmail/etc/bmiconfig.xml. So BMI
83 6.x users MUST set the bmi_config_file option.
86 3) Set up ACL control statement
88 To optimize performance, it makes sense only to process
89 messages coming from remote, untrusted sources with the BMI
90 server. To set up a messages for processing by the BMI
91 server, you MUST set the "bmi_run" control statement in any
92 ACL for an incoming message. You will typically do this in
93 an "accept" block in the "acl_check_rcpt" ACL. You should
94 use the "accept" block(s) that accept messages from remote
95 servers for your own domain(s). Here is an example that uses
96 the "accept" blocks from Exim's default configuration file:
99 accept domains = +local_domains
104 accept domains = +relay_to_domains
109 If bmi_run is not set in any ACL during reception of the
110 message, it will NOT be passed to the BMI server.
113 4) Setting up routers to use BMI verdicts
115 When a message has been run through the BMI server, one or
116 more "verdicts" are present. Different recipients can have
117 different verdicts. Each recipient is treated individually
118 during routing, so you can query the verdicts by recipient
119 at that stage. From Exim's view, a verdict can have the
122 o deliver the message normally
123 o deliver the message to an alternate location
124 o do not deliver the message
126 To query the verdict for a recipient, the implementation
127 offers the following tools:
130 - Boolean router preconditions. These can be used in any
131 router. For a simple implementation of BMI, these may be
132 all that you need. The following preconditions are
135 o bmi_deliver_default
137 This precondition is TRUE if the verdict for the
138 recipient is to deliver the message normally. If the
139 message has not been processed by the BMI server, this
140 variable defaults to TRUE.
142 o bmi_deliver_alternate
144 This precondition is TRUE if the verdict for the
145 recipient is to deliver the message to an alternate
146 location. You can get the location string from the
147 $bmi_alt_location expansion variable if you need it. See
148 further below. If the message has not been processed by
149 the BMI server, this variable defaults to FALSE.
153 This precondition is TRUE if the verdict for the
154 recipient is NOT to deliver the message to the
155 recipient. You will typically use this precondition in a
156 top-level blackhole router, like this:
158 # don't deliver messages handled by the BMI server
164 This router should be on top of all others, so messages
165 that should not be delivered do not reach other routers
166 at all. If the message has not been processed by
167 the BMI server, this variable defaults to FALSE.
170 - A list router precondition to query if rules "fired" on
171 the message for the recipient. Its name is "bmi_rule". You
172 use it by passing it a colon-separated list of rule
173 numbers. You can use this condition to route messages that
174 matched specific rules. Here is an example:
176 # special router for BMI rule #5, #8 and #11
180 data = postmaster@mydomain.com
183 - Expansion variables. Several expansion variables are set
184 during routing. You can use them in custom router
185 conditions, for example. The following variables are
188 o $bmi_base64_verdict
190 This variable will contain the BASE64 encoded verdict
191 for the recipient being routed. You can use it to add a
192 header to messages for tracking purposes, for example:
197 headers_add = X-Brightmail-Verdict: $bmi_base64_verdict
198 transport = local_delivery
200 If there is no verdict available for the recipient being
201 routed, this variable contains the empty string.
203 o $bmi_base64_tracker_verdict
205 This variable will contain a BASE64 encoded subset of
206 the verdict information concerning the "rules" that
207 fired on the message. You can add this string to a
208 header, commonly named "X-Brightmail-Tracker". Example:
213 headers_add = X-Brightmail-Tracker: $bmi_base64_tracker_verdict
214 transport = local_delivery
216 If there is no verdict available for the recipient being
217 routed, this variable contains the empty string.
221 If the verdict is to redirect the message to an
222 alternate location, this variable will contain the
223 alternate location string returned by the BMI server. In
224 its default configuration, this is a header-like string
225 that can be added to the message with "headers_add". If
226 there is no verdict available for the recipient being
227 routed, or if the message is to be delivered normally,
228 this variable contains the empty string.
232 This is an additional integer variable that can be used
233 to query if the message should be delivered at all. You
234 should use router preconditions instead if possible.
236 $bmi_deliver is '0': the message should NOT be delivered.
237 $bmi_deliver is '1': the message should be delivered.
240 IMPORTANT NOTE: Verdict inheritance.
241 The message is passed to the BMI server during message
242 reception, using the target addresses from the RCPT TO:
243 commands in the SMTP transaction. If recipients get expanded
244 or re-written (for example by aliasing), the new address(es)
245 inherit the verdict from the original address. This means
246 that verdicts also apply to all "child" addresses generated
247 from top-level addresses that were sent to the BMI server.
250 5) Using per-recipient opt-in information (Optional)
252 The BMI server features multiple scanning "profiles" for
253 individual recipients. These are usually stored in a LDAP
254 server and are queried by the BMI server itself. However,
255 you can also pass opt-in data for each recipient from the
256 MTA to the BMI server. This is particularly useful if you
257 already look up recipient data in Exim anyway (which can
258 also be stored in a SQL database or other source). This
259 implementation enables you to pass opt-in data to the BMI
260 server in the RCPT ACL. This works by setting the
261 'bmi_optin' modifier in a block of that ACL. If should be
262 set to a list of comma-separated strings that identify the
263 features which the BMI server should use for that particular
264 recipient. Ideally, you would use the 'bmi_optin' modifier
265 in the same ACL block where you set the 'bmi_run' control
266 flag. Here is an example that will pull opt-in data for each
267 recipient from a flat file called
268 '/etc/exim/bmi_optin_data'.
272 user1@mydomain.com: <OPTIN STRING1>:<OPTIN STRING2>
273 user2@thatdomain.com: <OPTIN STRING3>
278 accept domains = +relay_to_domains
281 bmi_optin = ${lookup{$local_part@$domain}lsearch{/etc/exim/bmi_optin_data}}
284 Of course, you can also use any other lookup method that
285 Exim supports, including LDAP, Postgres, MySQL, Oracle etc.,
286 as long as the result is a list of colon-separated opt-in
289 For a list of available opt-in strings, please contact your
290 Brightmail representative.
296 --------------------------------------------------------------
297 Distributed Checksum Clearinghouse; http://www.rhyolite.com/dcc/
301 In order to build exim with DCC support add
305 to your Makefile. (Re-)build/install exim. exim -d should show
306 EXPERIMENTAL_DCC under "Support for".
311 In the main section of exim.cf add at least
312 dccifd_address = /usr/local/dcc/var/dccifd
314 dccifd_address = <ip> <port>
316 In the DATA ACL you can use the new condition
319 After that "$dcc_header" contains the X-DCC-Header.
322 fail for overall "R", "G" from dccifd
323 defer for overall "T" from dccifd
324 accept for overall "A", "S" from dccifd
326 dcc = */defer_ok works as for spamd.
328 The "$dcc_result" variable contains the overall result from DCC
329 answer. There will an X-DCC: header added to the mail.
333 to greylist with DCC.
335 If you set, in the main section,
336 dcc_direct_add_header = true
337 then the dcc header will be added "in deep" and if the spool
338 file was already written it gets removed. This forces Exim to
339 write it again if needed. This helps to get the DCC Header
340 through to eg. SpamAssassin.
342 If you want to pass even more headers in the middle of the
343 DATA stage you can set
344 $acl_m_dcc_add_header
345 to tell the DCC routines to add more information; eg, you might set
346 this to some results from ClamAV. Be careful. Header syntax is
347 not checked and is added "as is".
349 In case you've troubles with sites sending the same queue items from several
350 hosts and fail to get through greylisting you can use
351 $acl_m_dcc_override_client_ip
353 Setting $acl_m_dcc_override_client_ip to an IP address overrides the default
354 of $sender_host_address. eg. use the following ACL in DATA stage:
356 warn set acl_m_dcc_override_client_ip = \
357 ${lookup{$sender_helo_name}nwildlsearch{/etc/mail/multipleip_sites}{$value}{}}
358 condition = ${if def:acl_m_dcc_override_client_ip}
359 log_message = dbg: acl_m_dcc_override_client_ip set to \
360 $acl_m_dcc_override_client_ip
362 Then set something like
363 # cat /etc/mail/multipleip_sites
364 mout-xforward.gmx.net 82.165.159.12
365 mout.gmx.net 212.227.15.16
367 Use a reasonable IP. eg. one the sending cluster actually uses.
371 DSN extra information
372 ---------------------
373 If compiled with EXPERIMENTAL_DSN_INFO extra information will be added
374 to DSN fail messages ("bounces"), when available. The intent is to aid
375 tracing of specific failing messages, when presented with a "bounce"
376 complaint and needing to search logs.
379 The remote MTA IP address, with port number if nonstandard.
381 Remote-MTA: X-ip; [127.0.0.1]:587
383 Several addresses may correspond to the (already available)
384 dns name for the remote MTA.
386 The remote MTA connect-time greeting.
388 X-Remote-MTA-smtp-greeting: X-str; 220 the.local.host.name ESMTP Exim x.yz Tue, 2 Mar 1999 09:44:33 +0000
390 This string sometimes presents the remote MTA's idea of its
391 own name, and sometimes identifies the MTA software.
393 The remote MTA response to HELO or EHLO.
395 X-Remote-MTA-helo-response: X-str; 250-the.local.host.name Hello localhost [127.0.0.1]
397 Only the first line of a multiline response is recorded.
399 This string sometimes presents the remote MTA's view of
400 the peer IP connecting to it.
402 The reporting MTA detailed diagnostic.
404 X-Exim-Diagnostic: X-str; SMTP error from remote mail server after RCPT TO:<d3@myhost.test.ex>: 550 hard error
406 This string sometimes give extra information over the
407 existing (already available) Diagnostic-Code field.
410 Note that non-RFC-documented field names and data types are used.
415 Queuefile is a pseudo transport which does not perform final delivery.
416 It simply copies the exim spool files out of the spool directory into
417 an external directory retaining the exim spool format.
419 The spool files can then be processed by external processes and then
420 requeued into exim spool directories for final delivery.
421 However, note carefully the warnings in the main documentation on
424 The motivation/inspiration for the transport is to allow external
425 processes to access email queued by exim and have access to all the
426 information which would not be available if the messages were delivered
427 to the process in the standard email formats.
429 The mailscanner package is one of the processes that can take advantage
430 of this transport to filter email.
432 The transport can be used in the same way as the other existing transports,
433 i.e by configuring a router to route mail to a transport configured with
434 the queuefile driver.
436 The transport only takes one option:
438 * directory - This is used to specify the directory messages should be
441 The generic transport options (body_only, current_directory, disable_logging,
442 debug_print, delivery_date_add, envelope_to_add, event_action, group,
443 headers_add, headers_only, headers_remove, headers_rewrite, home_directory,
444 initgroups, max_parallel, message_size_limit, rcpt_include_affixes,
445 retry_use_local_part, return_path, return_path_add, shadow_condition,
446 shadow_transport, transport_filter, transport_filter_timeout, user) are
449 Sample configuration:
461 directory = /var/spool/baruwa-scanner/input
464 In order to build exim with Queuefile transport support add or uncomment
466 EXPERIMENTAL_QUEUEFILE=yes
468 to your Local/Makefile. (Re-)build/install exim. exim -d should show
469 Experimental_QUEUEFILE in the line "Support for:".
474 Specification: https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-11
475 Note that this is not an RFC yet, so may change.
477 [RFC 8617 was published 2019/06. Draft 11 was 2018/01. A review of the
478 changes has not yet been done]
480 ARC is intended to support the utility of SPF and DKIM in the presence of
481 intermediaries in the transmission path - forwarders and mailinglists -
482 by establishing a cryptographically-signed chain in headers.
484 Normally one would only bother doing ARC-signing when functioning as
485 an intermediary. One might do verify for local destinations.
487 ARC uses the notion of a "ADministrative Management Domain" (ADMD).
488 Described in RFC 5598 (section 2.3), this is essentially a set of
489 mail-handling systems that mail transits that are all under the control
490 of one organisation. A label should be chosen to identify the ADMD.
491 Messages should be ARC-verified on entry to the ADMD, and ARC-signed on exit
495 Building with ARC Support
497 Enable using EXPERIMENTAL_ARC=yes in your Local/Makefile.
498 You must also have DKIM present (not disabled), and you very likely
499 want to have SPF enabled.
504 An ACL condition is provided to perform the "verifier actions" detailed
505 in section 6 of the above specification. It may be called from the DATA ACL
506 and succeeds if the result matches any of a given list.
507 It also records the highest ARC instance number (the chain size)
508 and verification result for later use in creating an Authentication-Results:
511 verify = arc/<acceptable_list> none:fail:pass
513 add_header = :at_start:${authresults {<admd-identifier>}}
515 Note that it would be wise to strip incoming messages of A-R headers
516 that claim to be from our own <admd-identifier>. Eg:
518 remove_header = \N^(?i)Authentication-Results\s*::\s*example.org;\N
520 There are four new variables:
522 $arc_state One of pass, fail, none
523 $arc_state_reason (if fail, why)
524 $arc_domains colon-sep list of ARC chain domains, in chain order.
525 problematic elements may have empty list elements
526 $arc_oldest_pass lowest passing instance number of chain
529 logwrite = oldest-p-ams: <${reduce {$lh_ARC-Authentication-Results:} \
531 {${if = {$arc_oldest_pass} \
532 {${extract {i}{${extract {1}{;}{$item}}}}} \
536 Receive log lines for an ARC pass will be tagged "ARC".
541 arc_sign = <admd-identifier> : <selector> : <privkey> [ : <options> ]
542 An option on the smtp transport, which constructs and prepends to the message
543 an ARC set of headers. The textually-first Authentication-Results: header
544 is used as a basis (you must have added one on entry to the ADMD).
545 Expanded as a whole; if unset, empty or forced-failure then no signing is done.
546 If it is set, all of the first three elements must be non-empty.
548 The fourth element is optional, and if present consists of a comma-separated list
549 of options. The options implemented are
551 timestamps Add a t= tag to the generated AMS and AS headers, with the
553 expire[=<val>] Add an x= tag to the generated AMS header, with an expiry time.
554 If the value <val> is an plain number it is used unchanged.
555 If it starts with a '+' then the following number is added
556 to the current time, as an offset in seconds.
557 If a value is not given it defaults to a one month offset.
559 [As of writing, gmail insist that a t= tag on the AS is mandatory]
562 * There must be an Authentication-Results header, presumably added by an ACL
563 while receiving the message, for the same ADMD, for arc_sign to succeed.
564 This requires careful coordination between inbound and outbound logic.
566 Only one A-R header is taken account of. This is a limitation versus
567 the ARC spec (which says that all A-R headers from within the ADMD must
570 * If passing a message to another system, such as a mailing-list manager
571 (MLM), between receipt and sending, be wary of manipulations to headers made
573 + For instance, Mailman with REMOVE_DKIM_HEADERS==3 might improve
574 deliverability in a pre-ARC world, but that option also renames the
575 Authentication-Results header, which breaks signing.
577 * Even if you use multiple DKIM keys for different domains, the ARC concept
578 should try to stick to one ADMD, so pick a primary domain and use that for
579 AR headers and outbound signing.
581 Signing is not compatible with cutthrough delivery; any (before expansion)
582 value set for the option will result in cutthrough delivery not being
583 used via the transport in question.
587 Dovecot authenticator via inet socket
588 --------------------------------------------------------------
589 If Dovecot is configured similar to :-
601 then an Exim authenticator can be configured :-
606 server_socket = dovecot_server_name 12345
608 server_set_id = $auth1
610 If the server_socket does not start with a / it is taken as a hostname (or IP);
611 and a whitespace-separated port number must be given.
616 Logging protocol unusual states
617 ---------------------------------------------------------------
618 An extra log_selector, "protocol_detail" has been added in the default build.
619 The name may change in future, hence the Experimenal status.
621 Currrently the only effect is to enable logging, under TLS,
622 of a TCP RST received directly after a QUIT (in server mode).
624 Outlook is consistently doing this; not waiting for the SMTP response
625 to its QUIT, not properly closing the TLS session and not properly closing
626 the TCP connection. Previously this resulted is an error from SSL_write
631 Limits ESMTP extension
632 ---------------------------------------------------------------
633 Per https://datatracker.ietf.org/doc/html/draft-freed-smtp-limits-01
634 (as of 2023/08/04, version -05 has been published. It does not seems
635 to be substantively different.)
637 If compiled with EXPERIMENTAL_ESMTP_LIMITS=yes :-
639 As a server, Exim will advertise, in the EHLO response, the limit for RCPT
640 commands set by the recipients_max main-section config option (if it is set),
641 and the limit for MAIL commands set by the smtp_accept_max_per_connection
644 Note that as of writing, smtp_accept_max_per_connection is expanded but
645 recipients_max is not.
647 A new main-section option "limits_advertise_hosts" controls whether
648 the limits are advertised; the default for the option is "*".
650 As a client, Exim will:
652 - note an advertised MAILMAX; the lower of the value given and the
653 value from the transport connection_max_messages option is used.
655 - note an advertised RCPTMAX; the lower of the
656 value given and the value from the transport max_rcpt option is used.
657 Parallisation of transactions is not done if due to a RCPTMAX, unlike
660 - note an advertised RCPTDOMAINMAX, and behave as if the transport
661 multi_domains option was set to false. The value advertised is ignored.
663 Values advertised are only noted for TLS connections and ones for which
664 the server does not advertise TLS support.
668 XCLIENT proxy support
669 ---------------------------------------------------------------
670 Per https://www.postfix.org/XCLIENT_README.html
672 XCLIENT is an ESMTP extension supporting an inbound proxy.
673 The only client immplementation known is in Nginx
674 (https://nginx.org/en/docs/mail/ngx_mail_proxy_module.html)
676 If compiled with EXPERIMENTAL_XCLIENT=yes :-
678 As a server, Exim will advertise XCLIENT support (conditional on a new option
679 "hosts_xclient") and service XCLIENT commands with parameters
686 A fresh HELO/EHLO is required after a succesful XCLIENT, and the usual
687 values are derived from that (making the HELO and PROTO paramemters redundant).
689 An XCLIENT command must give both ADDR and PORT parameters if no previous
690 XCLIENT has succeeded in the SMTP session.
693 $proxy_session variable becomes "yes"
694 $proxy_local_address, $proxy_local_port have the proxy "inside" values
695 $proxy_external_address, $proxy_external_port have the proxy "outside" values
696 $sender_host_address, $sender_host_port have the remot client values
698 --------------------------------------------------------------
700 --------------------------------------------------------------