DocĂ– Fix typo about spf lookup (experimental)
[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 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 ( 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 in your dynamic linker configuration
64 file (usually /etc/ 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 =
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:
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 Sender Policy Framework (SPF) support
296 --------------------------------------------------------------
298 To learn more about SPF, visit This
299 document does not explain the SPF fundamentals, you should
300 read and understand the implications of deploying SPF on your
301 system before doing so.
303 SPF support is added via the libspf2 library. Visit
307 to obtain a copy, then compile and install it. By default,
308 this will put headers in /usr/local/include and the static
309 library in /usr/local/lib.
311 To compile Exim with SPF support, set these additional flags in
312 Local/Makefile:
315 CFLAGS=-DSPF -I/usr/local/include
316 EXTRALIBS_EXIM=-L/usr/local/lib -lspf2
318 This assumes that the libspf2 files are installed in
319 their default locations.
321 You can now run SPF checks in incoming SMTP by using the "spf"
322 ACL condition in either the MAIL, RCPT or DATA ACLs. When
323 using it in the RCPT ACL, you can make the checks dependent on
324 the RCPT address (or domain), so you can check SPF records
325 only for certain target domains. This gives you the
326 possibility to opt-out certain customers that do not want
327 their mail to be subject to SPF checking.
329 The spf condition takes a list of strings on its right-hand
330 side. These strings describe the outcome of the SPF check for
331 which the spf condition should succeed. Valid strings are:
333 o pass The SPF check passed, the sending host
334 is positively verified by SPF.
335 o fail The SPF check failed, the sending host
336 is NOT allowed to send mail for the domain
337 in the envelope-from address.
338 o softfail The SPF check failed, but the queried
339 domain can't absolutely confirm that this
340 is a forgery.
341 o none The queried domain does not publish SPF
342 records.
343 o neutral The SPF check returned a "neutral" state.
344 This means the queried domain has published
345 a SPF record, but wants to allow outside
346 servers to send mail under its domain as well.
347 This should be treated like "none".
348 o permerror This indicates a syntax error in the SPF
349 record of the queried domain. You may deny
350 messages when this occurs. (Changed in 4.83)
351 o temperror This indicates a temporary error during all
352 processing, including Exim's SPF processing.
353 You may defer messages when this occurs.
354 (Changed in 4.83)
355 o err_temp Same as permerror, deprecated in 4.83, will be
356 removed in a future release.
357 o err_perm Same as temperror, deprecated in 4.83, will be
358 removed in a future release.
360 You can prefix each string with an exclamation mark to invert
361 its meaning, for example "!fail" will match all results but
362 "fail". The string list is evaluated left-to-right, in a
363 short-circuit fashion. When a string matches the outcome of
364 the SPF check, the condition succeeds. If none of the listed
365 strings matches the outcome of the SPF check, the condition
366 fails.
368 Here is an example to fail forgery attempts from domains that
369 publish SPF records:
371 /* -----------------
372 deny message = $sender_host_address is not allowed to send mail from ${if def:sender_address_domain {$sender_address_domain}{$sender_helo_name}}. \
373 Please see${if def:sender_address_domain {mfrom}{helo}};identity=${if def:sender_address_domain {$sender_address}{$sender_helo_name}};ip=$sender_host_address
374 spf = fail
375 --------------------- */
377 You can also give special treatment to specific domains:
379 /* -----------------
380 deny message = AOL sender, but not from AOL-approved relay.
381 sender_domains =
382 spf = fail:neutral
383 --------------------- */
385 Explanation: AOL publishes SPF records, but is liberal and
386 still allows non-approved relays to send mail from
387 This will result in a "neutral" state, while mail from genuine
388 AOL servers will result in "pass". The example above takes
389 this into account and treats "neutral" like "fail", but only
390 for Please note that this violates the SPF draft.
392 When the spf condition has run, it sets up several expansion
393 variables.
395 $spf_header_comment
396 This contains a human-readable string describing the outcome
397 of the SPF check. You can add it to a custom header or use
398 it for logging purposes.
400 $spf_received
401 This contains a complete Received-SPF: header that can be
402 added to the message. Please note that according to the SPF
403 draft, this header must be added at the top of the header
404 list. Please see section 10 on how you can do this.
406 Note: in case of "Best-guess" (see below), the convention is
407 to put this string in a header called X-SPF-Guess: instead.
409 $spf_result
410 This contains the outcome of the SPF check in string form,
411 one of pass, fail, softfail, none, neutral, permerror or
412 temperror.
414 $spf_smtp_comment
415 This contains a string that can be used in a SMTP response
416 to the calling party. Useful for "fail".
418 In addition to SPF, you can also perform checks for so-called
419 "Best-guess". Strictly speaking, "Best-guess" is not standard
420 SPF, but it is supported by the same framework that enables SPF
421 capability. Refer to
422 for a description of what it means.
424 To access this feature, simply use the spf_guess condition in place
425 of the spf one. For example:
427 /* -----------------
428 deny message = $sender_host_address doesn't look trustworthy to me
429 spf_guess = fail
430 --------------------- */
432 In case you decide to reject messages based on this check, you
433 should note that although it uses the same framework, "Best-guess"
434 is NOT SPF, and therefore you should not mention SPF at all in your
435 reject message.
437 When the spf_guess condition has run, it sets up the same expansion
438 variables as when spf condition is run, described above.
440 Additionally, since Best-guess is not standardized, you may redefine
441 what "Best-guess" means to you by redefining spf_guess variable in
442 global config. For example, the following:
444 /* -----------------
445 spf_guess = v=spf1 a/16 mx/16 ptr ?all
446 --------------------- */
448 would relax host matching rules to a broader network range.
451 A lookup expansion is also available. It takes an email
452 address as the key and an IP address as the database:
454 ${lookup {username@domain} spf {ip.ip.ip.ip}}
456 The lookup will return the same result strings as they can appear in
457 $spf_result (pass,fail,softfail,neutral,none,err_perm,err_temp).
458 Currently, only IPv4 addresses are supported.
462 SRS (Sender Rewriting Scheme) Support
463 --------------------------------------------------------------
465 Exiscan currently includes SRS support via Miles Wilton's
466 libsrs_alt library. The current version of the supported
467 library is 0.5, there are reports of 1.0 working.
469 In order to use SRS, you must get a copy of libsrs_alt from
473 (not the original source, which has disappeared.)
475 Unpack the tarball, then refer to MTAs/README.EXIM
476 to proceed. You need to set
480 in your Local/Makefile.
484 DCC Support
485 --------------------------------------------------------------
486 Distributed Checksum Clearinghouse;
488 *) Building exim
490 In order to build exim with DCC support add
494 to your Makefile. (Re-)build/install exim. exim -d should show
495 EXPERIMENTAL_DCC under "Support for".
498 *) Configuration
500 In the main section of add at least
501 dccifd_address = /usr/local/dcc/var/dccifd
502 or
503 dccifd_address = <ip> <port>
505 In the DATA ACL you can use the new condition
506 dcc = *
508 After that "$dcc_header" contains the X-DCC-Header.
510 Return values are:
511 fail for overall "R", "G" from dccifd
512 defer for overall "T" from dccifd
513 accept for overall "A", "S" from dccifd
515 dcc = */defer_ok works as for spamd.
517 The "$dcc_result" variable contains the overall result from DCC
518 answer. There will an X-DCC: header added to the mail.
520 Usually you'll use
521 defer !dcc = *
522 to greylist with DCC.
524 If you set, in the main section,
525 dcc_direct_add_header = true
526 then the dcc header will be added "in deep" and if the spool
527 file was already written it gets removed. This forces Exim to
528 write it again if needed. This helps to get the DCC Header
529 through to eg. SpamAssassin.
531 If you want to pass even more headers in the middle of the
532 DATA stage you can set
533 $acl_m_dcc_add_header
534 to tell the DCC routines to add more information; eg, you might set
535 this to some results from ClamAV. Be careful. Header syntax is
536 not checked and is added "as is".
538 In case you've troubles with sites sending the same queue items from several
539 hosts and fail to get through greylisting you can use
540 $acl_m_dcc_override_client_ip
542 Setting $acl_m_dcc_override_client_ip to an IP address overrides the default
543 of $sender_host_address. eg. use the following ACL in DATA stage:
545 warn set acl_m_dcc_override_client_ip = \
546 ${lookup{$sender_helo_name}nwildlsearch{/etc/mail/multipleip_sites}{$value}{}}
547 condition = ${if def:acl_m_dcc_override_client_ip}
548 log_message = dbg: acl_m_dcc_override_client_ip set to \
549 $acl_m_dcc_override_client_ip
551 Then set something like
552 # cat /etc/mail/multipleip_sites
556 Use a reasonable IP. eg. one the sending cluster actually uses.
558 DMARC Support
559 --------------------------------------------------------------
561 DMARC combines feedback from SPF, DKIM, and header From: in order
562 to attempt to provide better indicators of the authenticity of an
563 email. This document does not explain the fundamentals, you
564 should read and understand how it works by visiting the website at
567 DMARC support is added via the libopendmarc library. Visit:
571 to obtain a copy, or find it in your favorite rpm package
572 repository. If building from source, this description assumes
573 that headers will be in /usr/local/include, and that the libraries
574 are in /usr/local/lib.
576 1. To compile Exim with DMARC support, you must first enable SPF.
577 Please read the above section on enabling the EXPERIMENTAL_SPF
578 feature. You must also have DKIM support, so you cannot set the
579 DISABLE_DKIM feature. Once both of those conditions have been met
580 you can enable DMARC in Local/Makefile:
583 LDFLAGS += -lopendmarc
584 # CFLAGS += -I/usr/local/include
585 # LDFLAGS += -L/usr/local/lib
587 The first line sets the feature to include the correct code, and
588 the second line says to link the libopendmarc libraries into the
589 exim binary. The commented out lines should be uncommented if you
590 built opendmarc from source and installed in the default location.
591 Adjust the paths if you installed them elsewhere, but you do not
592 need to uncomment them if an rpm (or you) installed them in the
593 package controlled locations (/usr/include and /usr/lib).
596 2. Use the following global settings to configure DMARC:
598 Required:
599 dmarc_tld_file Defines the location of a text file of valid
600 top level domains the opendmarc library uses
601 during domain parsing. Maintained by Mozilla,
602 the most current version can be downloaded
603 from a link at
605 Optional:
606 dmarc_history_file Defines the location of a file to log results
607 of dmarc verification on inbound emails. The
608 contents are importable by the opendmarc tools
609 which will manage the data, send out DMARC
610 reports, and expire the data. Make sure the
611 directory of this file is writable by the user
612 exim runs as.
614 dmarc_forensic_sender The email address to use when sending a
615 forensic report detailing alignment failures
616 if a sender domain's dmarc record specifies it
617 and you have configured Exim to send them.
618 Default: do-not-reply@$default_hostname
621 3. By default, the DMARC processing will run for any remote,
622 non-authenticated user. It makes sense to only verify DMARC
623 status of messages coming from remote, untrusted sources. You can
624 use standard conditions such as hosts, senders, etc, to decide that
625 DMARC verification should *not* be performed for them and disable
626 DMARC with a control setting:
628 control = dmarc_disable_verify
630 A DMARC record can also specify a "forensic address", which gives
631 exim an email address to submit reports about failed alignment.
632 Exim does not do this by default because in certain conditions it
633 results in unintended information leakage (what lists a user might
634 be subscribed to, etc). You must configure exim to submit forensic
635 reports to the owner of the domain. If the DMARC record contains a
636 forensic address and you specify the control statement below, then
637 exim will send these forensic emails. It's also advised that you
638 configure a dmarc_forensic_sender because the default sender address
639 construction might be inadequate.
641 control = dmarc_enable_forensic
643 (AGAIN: You can choose not to send these forensic reports by simply
644 not putting the dmarc_enable_forensic control line at any point in
645 your exim config. If you don't tell it to send them, it will not
646 send them.)
648 There are no options to either control. Both must appear before
649 the DATA acl.
652 4. You can now run DMARC checks in incoming SMTP by using the
653 "dmarc_status" ACL condition in the DATA ACL. You are required to
654 call the spf condition first in the ACLs, then the "dmarc_status"
655 condition. Putting this condition in the ACLs is required in order
656 for a DMARC check to actually occur. All of the variables are set
657 up before the DATA ACL, but there is no actual DMARC check that
658 occurs until a "dmarc_status" condition is encountered in the ACLs.
660 The dmarc_status condition takes a list of strings on its
661 right-hand side. These strings describe recommended action based
662 on the DMARC check. To understand what the policy recommendations
663 mean, refer to the DMARC website above. Valid strings are:
665 o accept The DMARC check passed and the library recommends
666 accepting the email.
667 o reject The DMARC check failed and the library recommends
668 rejecting the email.
669 o quarantine The DMARC check failed and the library recommends
670 keeping it for further inspection.
671 o none The DMARC check passed and the library recommends
672 no specific action, neutral.
673 o norecord No policy section in the DMARC record for this
674 sender domain.
675 o nofrom Unable to determine the domain of the sender.
676 o temperror Library error or dns error.
677 o off The DMARC check was disabled for this email.
679 You can prefix each string with an exclamation mark to invert its
680 meaning, for example "!accept" will match all results but
681 "accept". The string list is evaluated left-to-right in a
682 short-circuit fashion. When a string matches the outcome of the
683 DMARC check, the condition succeeds. If none of the listed
684 strings matches the outcome of the DMARC check, the condition
685 fails.
687 Of course, you can also use any other lookup method that Exim
688 supports, including LDAP, Postgres, MySQL, etc, as long as the
689 result is a list of colon-separated strings.
691 Several expansion variables are set before the DATA ACL is
692 processed, and you can use them in this ACL. The following
693 expansion variables are available:
695 o $dmarc_status
696 This is a one word status indicating what the DMARC library
697 thinks of the email. It is a combination of the results of
698 DMARC record lookup and the SPF/DKIM/DMARC processing results
699 (if a DMARC record was found). The actual policy declared
700 in the DMARC record is in a separate expansion variable.
702 o $dmarc_status_text
703 This is a slightly longer, human readable status.
705 o $dmarc_used_domain
706 This is the domain which DMARC used to look up the DMARC
707 policy record.
709 o $dmarc_domain_policy
710 This is the policy declared in the DMARC record. Valid values
711 are "none", "reject" and "quarantine". It is blank when there
712 is any error, including no DMARC record.
714 o $dmarc_ar_header
715 This is the entire Authentication-Results header which you can
716 add using an add_header modifier.
719 5. How to enable DMARC advanced operation:
720 By default, Exim's DMARC configuration is intended to be
721 non-intrusive and conservative. To facilitate this, Exim will not
722 create any type of logging files without explicit configuration by
723 you, the admin. Nor will Exim send out any emails/reports about
724 DMARC issues without explicit configuration by you, the admin (other
725 than typical bounce messages that may come about due to ACL
726 processing or failure delivery issues).
728 In order to log statistics suitable to be imported by the opendmarc
729 tools, you need to:
730 a. Configure the global setting dmarc_history_file.
731 b. Configure cron jobs to call the appropriate opendmarc history
732 import scripts and truncating the dmarc_history_file.
734 In order to send forensic reports, you need to:
735 a. Configure the global setting dmarc_forensic_sender.
736 b. Configure, somewhere before the DATA ACL, the control option to
737 enable sending DMARC forensic reports.
740 6. Example usage:
741 (RCPT ACL)
742 warn domains = +local_domains
743 hosts = +local_hosts
744 control = dmarc_disable_verify
746 warn !domains = +screwed_up_dmarc_records
747 control = dmarc_enable_forensic
749 warn condition = (lookup if destined to mailing list)
750 set acl_m_mailing_list = 1
752 (DATA ACL)
753 warn dmarc_status = accept : none : off
754 !authenticated = *
755 log_message = DMARC DEBUG: $dmarc_status $dmarc_used_domain
756 add_header = $dmarc_ar_header
758 warn dmarc_status = !accept
759 !authenticated = *
760 log_message = DMARC DEBUG: '$dmarc_status' for $dmarc_used_domain
762 warn dmarc_status = quarantine
763 !authenticated = *
764 set $acl_m_quarantine = 1
765 # Do something in a transport with this flag variable
767 deny condition = ${if eq{$dmarc_domain_policy}{reject}}
768 condition = ${if eq{$acl_m_mailing_list}{1}}
769 message = Messages from $dmarc_used_domain break mailing lists
771 deny dmarc_status = reject
772 !authenticated = *
773 message = Message from $dmarc_used_domain failed sender's DMARC policy, REJECT
777 DANE
778 ------------------------------------------------------------
779 DNS-based Authentication of Named Entities, as applied
780 to SMTP over TLS, provides assurance to a client that
781 it is actually talking to the server it wants to rather
782 than some attacker operating a Man In The Middle (MITM)
783 operation. The latter can terminate the TLS connection
784 you make, and make another one to the server (so both
785 you and the server still think you have an encrypted
786 connection) and, if one of the "well known" set of
787 Certificate Authorities has been suborned - something
788 which *has* been seen already (2014), a verifiable
789 certificate (if you're using normal root CAs, eg. the
790 Mozilla set, as your trust anchors).
792 What DANE does is replace the CAs with the DNS as the
793 trust anchor. The assurance is limited to a) the possibility
794 that the DNS has been suborned, b) mistakes made by the
795 admins of the target server. The attack surface presented
796 by (a) is thought to be smaller than that of the set
797 of root CAs.
799 It also allows the server to declare (implicitly) that
800 connections to it should use TLS. An MITM could simply
801 fail to pass on a server's STARTTLS.
803 DANE scales better than having to maintain (and
804 side-channel communicate) copies of server certificates
805 for every possible target server. It also scales
806 (slightly) better than having to maintain on an SMTP
807 client a copy of the standard CAs bundle. It also
808 means not having to pay a CA for certificates.
810 DANE requires a server operator to do three things:
811 1) run DNSSEC. This provides assurance to clients
812 that DNS lookups they do for the server have not
813 been tampered with. The domain MX record applying
814 to this server, its A record, its TLSA record and
815 any associated CNAME records must all be covered by
817 2) add TLSA DNS records. These say what the server
818 certificate for a TLS connection should be.
819 3) offer a server certificate, or certificate chain,
820 in TLS connections which is traceable to the one
821 defined by (one of?) the TSLA records
823 There are no changes to Exim specific to server-side
824 operation of DANE.
826 The TLSA record for the server may have "certificate
827 usage" of DANE-TA(2) or DANE-EE(3). The latter specifies
828 the End Entity directly, i.e. the certificate involved
829 is that of the server (and should be the sole one transmitted
830 during the TLS handshake); this is appropriate for a
831 single system, using a self-signed certificate.
832 DANE-TA usage is effectively declaring a specific CA
833 to be used; this might be a private CA or a public,
834 well-known one. A private CA at simplest is just
835 a self-signed certificate which is used to sign
836 cerver certificates, but running one securely does
837 require careful arrangement. If a private CA is used
838 then either all clients must be primed with it, or
839 (probably simpler) the server TLS handshake must transmit
840 the entire certificate chain from CA to server-certificate.
841 If a public CA is used then all clients must be primed with it
842 (losing one advantage of DANE) - but the attack surface is
843 reduced from all public CAs to that single CA.
844 DANE-TA is commonly used for several services and/or
845 servers, each having a TLSA query-domain CNAME record,
846 all of which point to a single TLSA record.
848 The TLSA record should have a Selector field of SPKI(1)
849 and a Matching Type field of SHA2-512(2).
851 At the time of writing,
852 is useful for quickly generating TLSA records; and commands like
854 openssl x509 -in -pubkey -noout <certificate.pem \
855 | openssl rsa -outform der -pubin 2>/dev/null \
856 | openssl sha512 \
857 | awk '{print $2}'
859 are workable for 4th-field hashes.
861 For use with the DANE-TA model, server certificates
862 must have a correct name (SubjectName or SubjectAltName).
864 The use of OCSP-stapling should be considered, allowing
865 for fast revocation of certificates (which would otherwise
866 be limited by the DNS TTL on the TLSA records). However,
867 this is likely to only be usable with DANE-TA. NOTE: the
868 default of requesting OCSP for all hosts is modified iff
869 DANE is in use, to:
871 hosts_request_ocsp = ${if or { {= {0}{$tls_out_tlsa_usage}} \
872 {= {4}{$tls_out_tlsa_usage}} } \
873 {*}{}}
875 The (new) variable $tls_out_tlsa_usage is a bitfield with
876 numbered bits set for TLSA record usage codes.
877 The zero above means DANE was not in use,
878 the four means that only DANE-TA usage TLSA records were
879 found. If the definition of hosts_request_ocsp includes the
880 string "tls_out_tlsa_usage", they are re-expanded in time to
881 control the OCSP request.
883 This modification of hosts_request_ocsp is only done if
884 it has the default value of "*". Admins who change it, and
885 those who use hosts_require_ocsp, should consider the interaction
886 with DANE in their OCSP settings.
889 For client-side DANE there are two new smtp transport options,
890 hosts_try_dane and hosts_require_dane.
891 [ should they be domain-based rather than host-based? ]
893 Hosts_require_dane will result in failure if the target host
894 is not DNSSEC-secured.
896 DANE will only be usable if the target host has DNSSEC-secured
897 MX, A and TLSA records.
899 A TLSA lookup will be done if either of the above options match
900 and the host-lookup succeeded using dnssec.
901 If a TLSA lookup is done and succeeds, a DANE-verified TLS connection
902 will be required for the host. If it does not, the host will not
903 be used; there is no fallback to non-DANE or non-TLS.
905 If DANE is requested and useable (see above) the following transport
906 options are ignored:
907 hosts_require_tls
908 tls_verify_hosts
909 tls_try_verify_hosts
910 tls_verify_certificates
911 tls_crl
912 tls_verify_cert_hostnames
914 If DANE is not usable, whether requested or not, and CA-anchored
915 verification evaluation is wanted, the above variables should be set
916 appropriately.
918 Currently dnssec_request_domains must be active (need to think about that)
919 and dnssec_require_domains is ignored.
921 If verification was successful using DANE then the "CV" item
922 in the delivery log line will show as "CV=dane".
924 There is a new variable $tls_out_dane which will have "yes" if
925 verification succeeded using DANE and "no" otherwise (only useful
926 in combination with EXPERIMENTAL_EVENT), and a new variable
927 $tls_out_tlsa_usage (detailed above).
931 DSN extra information
932 ---------------------
933 If compiled with EXPERIMENTAL_DSN_INFO extra information will be added
934 to DSN fail messages ("bounces"), when available. The intent is to aid
935 tracing of specific failing messages, when presented with a "bounce"
936 complaint and needing to search logs.
939 The remote MTA IP address, with port number if nonstandard.
940 Example:
941 Remote-MTA: X-ip; []:587
942 Rationale:
943 Several addresses may correspond to the (already available)
944 dns name for the remote MTA.
946 The remote MTA connect-time greeting.
947 Example:
948 X-Remote-MTA-smtp-greeting: X-str; 220 ESMTP Exim x.yz Tue, 2 Mar 1999 09:44:33 +0000
949 Rationale:
950 This string sometimes presents the remote MTA's idea of its
951 own name, and sometimes identifies the MTA software.
953 The remote MTA response to HELO or EHLO.
954 Example:
955 X-Remote-MTA-helo-response: X-str; Hello localhost []
956 Limitations:
957 Only the first line of a multiline response is recorded.
958 Rationale:
959 This string sometimes presents the remote MTA's view of
960 the peer IP connecting to it.
962 The reporting MTA detailed diagnostic.
963 Example:
964 X-Exim-Diagnostic: X-str; SMTP error from remote mail server after RCPT TO:<d3@myhost.test.ex>: 550 hard error
965 Rationale:
966 This string sometimes give extra information over the
967 existing (already available) Diagnostic-Code field.
970 Note that non-RFC-documented field names and data types are used.
973 LMDB Lookup support
974 -------------------
975 LMDB is an ultra-fast, ultra-compact, crash-proof key-value embedded data store.
976 It is modeled loosely on the BerkeleyDB API. You should read about the feature
977 set as well as operation modes at
979 LMDB single key lookup support is provided by linking to the LMDB C library.
980 The current implementation does not support writing to the LMDB database.
982 Visit to download the library or find it in your
983 operating systems package repository.
985 If building from source, this description assumes that headers will be in
986 /usr/local/include, and that the libraries are in /usr/local/lib.
988 1. In order to build exim with LMDB lookup support add or uncomment
992 to your Local/Makefile. (Re-)build/install exim. exim -d should show
993 Experimental_LMDB in the line "Support for:".
996 LDFLAGS += -llmdb
997 # CFLAGS += -I/usr/local/include
998 # LDFLAGS += -L/usr/local/lib
1000 The first line sets the feature to include the correct code, and
1001 the second line says to link the LMDB libraries into the
1002 exim binary. The commented out lines should be uncommented if you
1003 built LMDB from source and installed in the default location.
1004 Adjust the paths if you installed them elsewhere, but you do not
1005 need to uncomment them if an rpm (or you) installed them in the
1006 package controlled locations (/usr/include and /usr/lib).
1008 2. Create your LMDB files, you can use the mdb_load utility which is
1009 part of the LMDB distribution our your favourite language bindings.
1011 3. Add the single key lookups to your exim.conf file, example lookups
1012 are below.
1014 ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}}
1015 ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}fail}
1016 ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}}
1019 Queuefile transport
1020 -------------------
1021 Queuefile is a pseudo transport which does not perform final delivery.
1022 It simply copies the exim spool files out of the spool directory into
1023 an external directory retaining the exim spool format.
1025 The spool files can then be processed by external processes and then
1026 requeued into exim spool directories for final delivery.
1028 The motivation/inspiration for the transport is to allow external
1029 processes to access email queued by exim and have access to all the
1030 information which would not be available if the messages were delivered
1031 to the process in the standard email formats.
1033 The mailscanner package is one of the processes that can take advantage
1034 of this transport to filter email.
1036 The transport can be used in the same way as the other existing transports,
1037 i.e by configuring a router to route mail to a transport configured with
1038 the queuefile driver.
1040 The transport only takes one option:
1042 * directory - This is used to specify the directory messages should be
1043 copied to
1045 The generic transport options (body_only, current_directory, disable_logging,
1046 debug_print, delivery_date_add, envelope_to_add, event_action, group,
1047 headers_add, headers_only, headers_remove, headers_rewrite, home_directory,
1048 initgroups, max_parallel, message_size_limit, rcpt_include_affixes,
1049 retry_use_local_part, return_path, return_path_add, shadow_condition,
1050 shadow_transport, transport_filter, transport_filter_timeout, user) are
1051 ignored.
1053 Sample configuration:
1055 (Router)
1057 scan:
1058 driver = accept
1059 transport = scan
1061 (Transport)
1063 scan:
1064 driver = queuefile
1065 directory = /var/spool/baruwa-scanner/input
1068 In order to build exim with Queuefile transport support add or uncomment
1072 to your Local/Makefile. (Re-)build/install exim. exim -d should show
1073 Experimental_QUEUEFILE in the line "Support for:".
1076 --------------------------------------------------------------
1077 End of file
1078 --------------------------------------------------------------