[exim.git] / doc / doc-txt / experimental-spec.txt
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
15 "BMI" from now on.
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
30 following steps:
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
35 file)
36 4) Set up your routers to use BMI verdicts (routers section
37 of the config file).
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:
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
60 this.
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
100 endpass
101 verify = recipient
102 control = bmi_run
104 accept domains = +relay_to_domains
105 endpass
106 verify = recipient
107 control = bmi_run
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
120 following outcomes:
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
133 available:
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.
151 o bmi_dont_deliver
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
159 bmi_blackhole:
160 driver = redirect
161 bmi_dont_deliver
162 data = :blackhole:
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
177 bmi_rule_redirect:
178 driver = redirect
179 bmi_rule = 5:8:11
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
186 available:
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:
194 localuser:
195 driver = accept
196 check_local_user
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:
210 localuser:
211 driver = accept
212 check_local_user
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.
219 o $bmi_alt_location
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.
230 o $bmi_deliver
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'.
270 The file format:
272 user1@mydomain.com: <OPTIN STRING1>:<OPTIN STRING2>
273 user2@thatdomain.com: <OPTIN STRING3>
276 The example:
278 accept domains = +relay_to_domains
279 endpass
280 verify = recipient
281 bmi_optin = ${lookup{$local_part@$domain}lsearch{/etc/exim/bmi_optin_data}}
282 control = bmi_run
284 Of course, you can also use any other lookup method that
285 Exim supports, including LDAP, Postgres, MySQL, Oracle etc.,
286 as long as the result is a list of colon-separated opt-in
287 strings.
289 For a list of available opt-in strings, please contact your
290 Brightmail representative.
295 SRS (Sender Rewriting Scheme) Support
296 --------------------------------------------------------------
298 Exiscan currently includes SRS support via Miles Wilton's
299 libsrs_alt library. The current version of the supported
300 library is 0.5, there are reports of 1.0 working.
302 In order to use SRS, you must get a copy of libsrs_alt from
304 https://opsec.eu/src/srs/
306 (not the original source, which has disappeared.)
308 Unpack the tarball, then refer to MTAs/README.EXIM
309 to proceed. You need to set
313 in your Local/Makefile.
317 DCC Support
318 --------------------------------------------------------------
319 Distributed Checksum Clearinghouse; http://www.rhyolite.com/dcc/
321 *) Building exim
323 In order to build exim with DCC support add
327 to your Makefile. (Re-)build/install exim. exim -d should show
328 EXPERIMENTAL_DCC under "Support for".
331 *) Configuration
333 In the main section of exim.cf add at least
334 dccifd_address = /usr/local/dcc/var/dccifd
335 or
336 dccifd_address = <ip> <port>
338 In the DATA ACL you can use the new condition
339 dcc = *
341 After that "$dcc_header" contains the X-DCC-Header.
343 Return values are:
344 fail for overall "R", "G" from dccifd
345 defer for overall "T" from dccifd
346 accept for overall "A", "S" from dccifd
348 dcc = */defer_ok works as for spamd.
350 The "$dcc_result" variable contains the overall result from DCC
351 answer. There will an X-DCC: header added to the mail.
353 Usually you'll use
354 defer !dcc = *
355 to greylist with DCC.
357 If you set, in the main section,
358 dcc_direct_add_header = true
359 then the dcc header will be added "in deep" and if the spool
360 file was already written it gets removed. This forces Exim to
361 write it again if needed. This helps to get the DCC Header
362 through to eg. SpamAssassin.
364 If you want to pass even more headers in the middle of the
365 DATA stage you can set
366 $acl_m_dcc_add_header
367 to tell the DCC routines to add more information; eg, you might set
368 this to some results from ClamAV. Be careful. Header syntax is
369 not checked and is added "as is".
371 In case you've troubles with sites sending the same queue items from several
372 hosts and fail to get through greylisting you can use
373 $acl_m_dcc_override_client_ip
375 Setting $acl_m_dcc_override_client_ip to an IP address overrides the default
376 of $sender_host_address. eg. use the following ACL in DATA stage:
378 warn set acl_m_dcc_override_client_ip = \
379 ${lookup{$sender_helo_name}nwildlsearch{/etc/mail/multipleip_sites}{$value}{}}
380 condition = ${if def:acl_m_dcc_override_client_ip}
381 log_message = dbg: acl_m_dcc_override_client_ip set to \
382 $acl_m_dcc_override_client_ip
384 Then set something like
385 # cat /etc/mail/multipleip_sites
386 mout-xforward.gmx.net
387 mout.gmx.net
389 Use a reasonable IP. eg. one the sending cluster actually uses.
393 DMARC Support
394 --------------------------------------------------------------
396 DMARC combines feedback from SPF, DKIM, and header From: in order
397 to attempt to provide better indicators of the authenticity of an
398 email. This document does not explain the fundamentals, you
399 should read and understand how it works by visiting the website at
400 http://www.dmarc.org/.
402 DMARC support is added via the libopendmarc library. Visit:
404 http://sourceforge.net/projects/opendmarc/
406 to obtain a copy, or find it in your favorite rpm package
407 repository. If building from source, this description assumes
408 that headers will be in /usr/local/include, and that the libraries
409 are in /usr/local/lib.
411 1. To compile Exim with DMARC support, you must first enable SPF.
412 Please read the Local/Makefile comments on enabling the SUPPORT_SPF
413 feature. You must also have DKIM support, so you cannot set the
414 DISABLE_DKIM feature. Once both of those conditions have been met
415 you can enable DMARC in Local/Makefile:
418 LDFLAGS += -lopendmarc
419 # CFLAGS += -I/usr/local/include
420 # LDFLAGS += -L/usr/local/lib
422 The first line sets the feature to include the correct code, and
423 the second line says to link the libopendmarc libraries into the
424 exim binary. The commented out lines should be uncommented if you
425 built opendmarc from source and installed in the default location.
426 Adjust the paths if you installed them elsewhere, but you do not
427 need to uncomment them if an rpm (or you) installed them in the
428 package controlled locations (/usr/include and /usr/lib).
431 2. Use the following global settings to configure DMARC:
433 Required:
434 dmarc_tld_file Defines the location of a text file of valid
435 top level domains the opendmarc library uses
436 during domain parsing. Maintained by Mozilla,
437 the most current version can be downloaded
438 from a link at http://publicsuffix.org/list/.
439 See also util/renew-opendmarc-tlds.sh script.
441 Optional:
442 dmarc_history_file Defines the location of a file to log results
443 of dmarc verification on inbound emails. The
444 contents are importable by the opendmarc tools
445 which will manage the data, send out DMARC
446 reports, and expire the data. Make sure the
447 directory of this file is writable by the user
448 exim runs as.
450 dmarc_forensic_sender Alternate email address to use when sending a
451 forensic report detailing alignment failures
452 if a sender domain's dmarc record specifies it
453 and you have configured Exim to send them.
455 If set, this is expanded and used for the
456 From: header line; the address is extracted
457 from it and used for the envelope from.
458 If not set, the From: header is expanded from
459 the dsn_from option, and <> is used for the
460 envelope from.
462 Default: unset.
465 3. By default, the DMARC processing will run for any remote,
466 non-authenticated user. It makes sense to only verify DMARC
467 status of messages coming from remote, untrusted sources. You can
468 use standard conditions such as hosts, senders, etc, to decide that
469 DMARC verification should *not* be performed for them and disable
470 DMARC with a control setting:
472 control = dmarc_disable_verify
474 A DMARC record can also specify a "forensic address", which gives
475 exim an email address to submit reports about failed alignment.
476 Exim does not do this by default because in certain conditions it
477 results in unintended information leakage (what lists a user might
478 be subscribed to, etc). You must configure exim to submit forensic
479 reports to the owner of the domain. If the DMARC record contains a
480 forensic address and you specify the control statement below, then
481 exim will send these forensic emails. It's also advised that you
482 configure a dmarc_forensic_sender because the default sender address
483 construction might be inadequate.
485 control = dmarc_enable_forensic
487 (AGAIN: You can choose not to send these forensic reports by simply
488 not putting the dmarc_enable_forensic control line at any point in
489 your exim config. If you don't tell it to send them, it will not
490 send them.)
492 There are no options to either control. Both must appear before
493 the DATA acl.
496 4. You can now run DMARC checks in incoming SMTP by using the
497 "dmarc_status" ACL condition in the DATA ACL. You are required to
498 call the spf condition first in the ACLs, then the "dmarc_status"
499 condition. Putting this condition in the ACLs is required in order
500 for a DMARC check to actually occur. All of the variables are set
501 up before the DATA ACL, but there is no actual DMARC check that
502 occurs until a "dmarc_status" condition is encountered in the ACLs.
504 The dmarc_status condition takes a list of strings on its
505 right-hand side. These strings describe recommended action based
506 on the DMARC check. To understand what the policy recommendations
507 mean, refer to the DMARC website above. Valid strings are:
509 o accept The DMARC check passed and the library recommends
510 accepting the email.
511 o reject The DMARC check failed and the library recommends
512 rejecting the email.
513 o quarantine The DMARC check failed and the library recommends
514 keeping it for further inspection.
515 o none The DMARC check passed and the library recommends
516 no specific action, neutral.
517 o norecord No policy section in the DMARC record for this
518 sender domain.
519 o nofrom Unable to determine the domain of the sender.
520 o temperror Library error or dns error.
521 o off The DMARC check was disabled for this email.
523 You can prefix each string with an exclamation mark to invert its
524 meaning, for example "!accept" will match all results but
525 "accept". The string list is evaluated left-to-right in a
526 short-circuit fashion. When a string matches the outcome of the
527 DMARC check, the condition succeeds. If none of the listed
528 strings matches the outcome of the DMARC check, the condition
529 fails.
531 Of course, you can also use any other lookup method that Exim
532 supports, including LDAP, Postgres, MySQL, etc, as long as the
533 result is a list of colon-separated strings.
535 Performing the check sets up information used by the
536 ${authresults } expansion item.
538 Several expansion variables are set before the DATA ACL is
539 processed, and you can use them in this ACL. The following
540 expansion variables are available:
542 o $dmarc_status
543 This is a one word status indicating what the DMARC library
544 thinks of the email. It is a combination of the results of
545 DMARC record lookup and the SPF/DKIM/DMARC processing results
546 (if a DMARC record was found). The actual policy declared
547 in the DMARC record is in a separate expansion variable.
549 o $dmarc_status_text
550 This is a slightly longer, human readable status.
552 o $dmarc_used_domain
553 This is the domain which DMARC used to look up the DMARC
554 policy record.
556 o $dmarc_domain_policy
557 This is the policy declared in the DMARC record. Valid values
558 are "none", "reject" and "quarantine". It is blank when there
559 is any error, including no DMARC record.
561 A now-redundant variable $dmarc_ar_header has now been withdrawn.
562 Use the ${authresults } expansion instead.
565 5. How to enable DMARC advanced operation:
566 By default, Exim's DMARC configuration is intended to be
567 non-intrusive and conservative. To facilitate this, Exim will not
568 create any type of logging files without explicit configuration by
569 you, the admin. Nor will Exim send out any emails/reports about
570 DMARC issues without explicit configuration by you, the admin (other
571 than typical bounce messages that may come about due to ACL
572 processing or failure delivery issues).
574 In order to log statistics suitable to be imported by the opendmarc
575 tools, you need to:
576 a. Configure the global setting dmarc_history_file.
577 b. Configure cron jobs to call the appropriate opendmarc history
578 import scripts and truncating the dmarc_history_file.
580 In order to send forensic reports, you need to:
581 a. Configure the global setting dmarc_forensic_sender.
582 b. Configure, somewhere before the DATA ACL, the control option to
583 enable sending DMARC forensic reports.
586 6. Example usage:
587 (RCPT ACL)
588 warn domains = +local_domains
589 hosts = +local_hosts
590 control = dmarc_disable_verify
592 warn !domains = +screwed_up_dmarc_records
593 control = dmarc_enable_forensic
595 warn condition = (lookup if destined to mailing list)
596 set acl_m_mailing_list = 1
598 (DATA ACL)
599 warn dmarc_status = accept : none : off
600 !authenticated = *
601 log_message = DMARC DEBUG: $dmarc_status $dmarc_used_domain
603 warn dmarc_status = !accept
604 !authenticated = *
605 log_message = DMARC DEBUG: '$dmarc_status' for $dmarc_used_domain
607 warn dmarc_status = quarantine
608 !authenticated = *
609 set $acl_m_quarantine = 1
610 # Do something in a transport with this flag variable
612 deny condition = ${if eq{$dmarc_domain_policy}{reject}}
613 condition = ${if eq{$acl_m_mailing_list}{1}}
614 message = Messages from $dmarc_used_domain break mailing lists
616 deny dmarc_status = reject
617 !authenticated = *
618 message = Message from $dmarc_used_domain failed sender's DMARC policy, REJECT
620 warn add_header = :at_start:${authresults {$primary_hostname}}
624 DSN extra information
625 ---------------------
626 If compiled with EXPERIMENTAL_DSN_INFO extra information will be added
627 to DSN fail messages ("bounces"), when available. The intent is to aid
628 tracing of specific failing messages, when presented with a "bounce"
629 complaint and needing to search logs.
632 The remote MTA IP address, with port number if nonstandard.
633 Example:
634 Remote-MTA: X-ip; []:587
635 Rationale:
636 Several addresses may correspond to the (already available)
637 dns name for the remote MTA.
639 The remote MTA connect-time greeting.
640 Example:
641 X-Remote-MTA-smtp-greeting: X-str; 220 the.local.host.name ESMTP Exim x.yz Tue, 2 Mar 1999 09:44:33 +0000
642 Rationale:
643 This string sometimes presents the remote MTA's idea of its
644 own name, and sometimes identifies the MTA software.
646 The remote MTA response to HELO or EHLO.
647 Example:
648 X-Remote-MTA-helo-response: X-str; 250-the.local.host.name Hello localhost []
649 Limitations:
650 Only the first line of a multiline response is recorded.
651 Rationale:
652 This string sometimes presents the remote MTA's view of
653 the peer IP connecting to it.
655 The reporting MTA detailed diagnostic.
656 Example:
657 X-Exim-Diagnostic: X-str; SMTP error from remote mail server after RCPT TO:<d3@myhost.test.ex>: 550 hard error
658 Rationale:
659 This string sometimes give extra information over the
660 existing (already available) Diagnostic-Code field.
663 Note that non-RFC-documented field names and data types are used.
666 LMDB Lookup support
667 -------------------
668 LMDB is an ultra-fast, ultra-compact, crash-proof key-value embedded data store.
669 It is modeled loosely on the BerkeleyDB API. You should read about the feature
670 set as well as operation modes at https://symas.com/products/lightning-memory-mapped-database/
672 LMDB single key lookup support is provided by linking to the LMDB C library.
673 The current implementation does not support writing to the LMDB database.
675 Visit https://github.com/LMDB/lmdb to download the library or find it in your
676 operating systems package repository.
678 If building from source, this description assumes that headers will be in
679 /usr/local/include, and that the libraries are in /usr/local/lib.
681 1. In order to build exim with LMDB lookup support add or uncomment
685 to your Local/Makefile. (Re-)build/install exim. exim -d should show
686 Experimental_LMDB in the line "Support for:".
689 LDFLAGS += -llmdb
690 # CFLAGS += -I/usr/local/include
691 # LDFLAGS += -L/usr/local/lib
693 The first line sets the feature to include the correct code, and
694 the second line says to link the LMDB libraries into the
695 exim binary. The commented out lines should be uncommented if you
696 built LMDB from source and installed in the default location.
697 Adjust the paths if you installed them elsewhere, but you do not
698 need to uncomment them if an rpm (or you) installed them in the
699 package controlled locations (/usr/include and /usr/lib).
701 2. Create your LMDB files, you can use the mdb_load utility which is
702 part of the LMDB distribution our your favourite language bindings.
704 3. Add the single key lookups to your exim.conf file, example lookups
705 are below.
707 ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}}
708 ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}fail}
709 ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}}
712 Queuefile transport
713 -------------------
714 Queuefile is a pseudo transport which does not perform final delivery.
715 It simply copies the exim spool files out of the spool directory into
716 an external directory retaining the exim spool format.
718 The spool files can then be processed by external processes and then
719 requeued into exim spool directories for final delivery.
720 However, note carefully the warnings in the main documentation on
721 qpool file formats.
723 The motivation/inspiration for the transport is to allow external
724 processes to access email queued by exim and have access to all the
725 information which would not be available if the messages were delivered
726 to the process in the standard email formats.
728 The mailscanner package is one of the processes that can take advantage
729 of this transport to filter email.
731 The transport can be used in the same way as the other existing transports,
732 i.e by configuring a router to route mail to a transport configured with
733 the queuefile driver.
735 The transport only takes one option:
737 * directory - This is used to specify the directory messages should be
738 copied to. Expanded.
740 The generic transport options (body_only, current_directory, disable_logging,
741 debug_print, delivery_date_add, envelope_to_add, event_action, group,
742 headers_add, headers_only, headers_remove, headers_rewrite, home_directory,
743 initgroups, max_parallel, message_size_limit, rcpt_include_affixes,
744 retry_use_local_part, return_path, return_path_add, shadow_condition,
745 shadow_transport, transport_filter, transport_filter_timeout, user) are
746 ignored.
748 Sample configuration:
750 (Router)
752 scan:
753 driver = accept
754 transport = scan
756 (Transport)
758 scan:
759 driver = queuefile
760 directory = /var/spool/baruwa-scanner/input
763 In order to build exim with Queuefile transport support add or uncomment
767 to your Local/Makefile. (Re-)build/install exim. exim -d should show
768 Experimental_QUEUEFILE in the line "Support for:".
771 ARC support
772 -----------
773 Specification: https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-11
774 Note that this is not an RFC yet, so may change.
776 ARC is intended to support the utility of SPF and DKIM in the presence of
777 intermediaries in the transmission path - forwarders and mailinglists -
778 by establishing a cryptographically-signed chain in headers.
780 Normally one would only bother doing ARC-signing when functioning as
781 an intermediary. One might do verify for local destinations.
783 ARC uses the notion of a "ADministrative Management Domain" (ADMD).
784 Described in RFC 5598 (section 2.3), this is essentially the set of
785 mail-handling systems that the mail transits. A label should be chosen to
786 identify the ADMD. Messages should be ARC-verified on entry to the ADMD,
787 and ARC-signed on exit from it.
790 Verification
791 --
792 An ACL condition is provided to perform the "verifier actions" detailed
793 in section 6 of the above specification. It may be called from the DATA ACL
794 and succeeds if the result matches any of a given list.
795 It also records the highest ARC instance number (the chain size)
796 and verification result for later use in creating an Authentication-Results:
797 standard header.
799 verify = arc/<acceptable_list> none:fail:pass
801 add_header = :at_start:${authresults {<admd-identifier>}}
803 Note that it would be wise to strip incoming messages of A-R headers
804 that claim to be from our own <admd-identifier>.
806 There are three new variables: $arc_state, $arc_state_reason, $arc_domains:
808 $arc_state One of pass, fail, none
809 $arc_state_reason (if fail, why)
810 $arc_domains colon-sep list of ARC chain domains, in chain order.
811 problematic elements may have empty list elements
812 $arc_oldest_pass lowest passing instance number of chain
814 Example:
815 logwrite = oldest-p-ams: <${reduce {$lh_ARC-Authentication-Results:} \
816 {} \
817 {${if = {$arc_oldest_pass} \
818 {${extract {i}{${extract {1}{;}{$item}}}}} \
819 {$item} {$value}}} \
820 }>
822 Receive log lines for an ARC pass will be tagged "ARC".
825 Signing
826 --
827 arc_sign = <admd-identifier> : <selector> : <privkey> [ : <options> ]
828 An option on the smtp transport, which constructs and prepends to the message
829 an ARC set of headers. The textually-first Authentication-Results: header
830 is used as a basis (you must have added one on entry to the ADMD).
831 Expanded as a whole; if unset, empty or forced-failure then no signing is done.
832 If it is set, all of the first three elements must be non-empty.
834 The fourth element is optional, and if present consists of a comma-separated list
835 of options. The options implemented are
837 timestamps Add a t= tag to the generated AMS and AS headers, with the
838 current time.
839 expire[=<val>] Add an x= tag to the generated AMS header, with an expiry time.
840 If the value <val> is an plain number it is used unchanged.
841 If it starts with a '+' then the following number is added
842 to the current time, as an offset in seconds.
843 If a value is not given it defaults to a one month offset.
845 [As of writing, gmail insist that a t= tag on the AS is mandatory]
847 Caveats:
848 * There must be an Authentication-Results header, presumably added by an ACL
849 while receiving the message, for the same ADMD, for arc_sign to succeed.
850 This requires careful coordination between inbound and outbound logic.
852 Only one A-R header is taken account of. This is a limitation versus
853 the ARC spec (which says that all A-R headers from within the ADMD must
854 be used).
856 * If passing a message to another system, such as a mailing-list manager
857 (MLM), between receipt and sending, be wary of manipulations to headers made
858 by the MLM.
859 + For instance, Mailman with REMOVE_DKIM_HEADERS==3 might improve
860 deliverability in a pre-ARC world, but that option also renames the
861 Authentication-Results header, which breaks signing.
863 * Even if you use multiple DKIM keys for different domains, the ARC concept
864 should try to stick to one ADMD, so pick a primary domain and use that for
865 AR headers and outbound signing.
867 Signing is not compatible with cutthrough delivery; any (before expansion)
868 value set for the option will result in cutthrough delivery not being
869 used via the transport in question.
874 REQUIRETLS support
875 ------------------
876 Ref: https://tools.ietf.org/html/draft-ietf-uta-smtp-require-tls-03
878 If compiled with EXPERIMENTAL_REQUIRETLS support is included for this
879 feature, where a REQUIRETLS option is added to the MAIL command.
880 The client may not retry in clear if the MAIL+REQUIRETLS fails (or was never
881 offered), and the server accepts an obligation that any onward transmission
882 by SMTP of the messages accepted will also use REQUIRETLS - or generate a
883 fail DSN.
885 The Exim implementation includes
886 - a main-part option tls_advertise_requiretls; host list, default "*"
887 - an observability variable $requiretls returning yes/no
888 - an ACL "control = requiretls" modifier for setting the requirement
889 - Log lines and Received: headers capitalise the S in the protocol
890 element: "P=esmtpS"
892 Differences from spec:
893 - we support upgrading the requirement for REQUIRETLS, including adding
894 it from cold, within an MTA. The spec only define the sourcing MUA
895 as being able to source the requirement, and makes no mention of upgrade.
896 - No support is coded for the RequireTLS header (which can be used
897 to annul DANE and/or STS policiy). [this can _almost_ be done in
898 transport option expansions, but not quite: it requires tha DANE-present
899 but STARTTLS-failing targets fallback to cleartext, which current DANE
900 coding specifically blocks]
902 Note that REQUIRETLS is only advertised once a TLS connection is achieved
903 (in contrast to STARTTLS). If you want to check the advertising, do something
904 like "swaks -s -tls -q HELO".
907 --------------------------------------------------------------
908 End of file
909 --------------------------------------------------------------