Docs: tweak ARC description
[exim.git] / doc / doc-txt / experimental-spec.txt
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1From time to time, experimental features may be added to Exim.
2While a feature is experimental, there will be a build-time
3option whose name starts "EXPERIMENTAL_" that must be set in
4order to include the feature. This file contains information
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5about experimental features, all of which are unstable and
6liable to incompatible change.
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7
8
4c04137d 9Brightmail AntiSpam (BMI) support
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10--------------------------------------------------------------
11
12Brightmail AntiSpam is a commercial package. Please see
13http://www.brightmail.com for more information on
14the product. For the sake of clarity, we'll refer to it as
15"BMI" from now on.
16
17
180) BMI concept and implementation overview
19
20In contrast to how spam-scanning with SpamAssassin is
21implemented in exiscan-acl, BMI is more suited for per
22-recipient scanning of messages. However, each messages is
23scanned only once, but multiple "verdicts" for multiple
24recipients can be returned from the BMI server. The exiscan
25implementation passes the message to the BMI server just
26before accepting it. It then adds the retrieved verdicts to
27the messages header file in the spool. These verdicts can then
28be queried in routers, where operation is per-recipient
29instead of per-message. To use BMI, you need to take the
30following steps:
31
32 1) Compile Exim with BMI support
3ec3e3bb 33 2) Set up main BMI options (top section of Exim config file)
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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.
39
8ff3788c 40These four steps are explained in more details below.
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41
421) Adding support for BMI at compile time
43
44 To compile with BMI support, you need to link Exim against
4c04137d 45 the Brightmail client SDK, consisting of a library
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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:
50
51 EXPERIMENTAL_BRIGHTMAIL=yes
47bbda99 52 CFLAGS=-I/path/to/the/dir/with/the/includefile
ee161e8f 53 EXTRALIBS_EXIM=-L/path/to/the/dir/with/the/library -lbmiclient_single
8ff3788c 54
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55 If you use other CFLAGS or EXTRALIBS_EXIM settings then
56 merge the content of these lines with them.
57
7c0c8547 58 Note for BMI6.x users: You'll also have to add -lxml2_single
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59 to the EXTRALIBS_EXIM line. Users of 5.5x do not need to do
60 this.
8ff3788c 61
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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.
67
68
3ec3e3bb 692) Setting up BMI support in the Exim main configuration
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3ec3e3bb 71 To enable BMI support in the main Exim configuration, you
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72 should set the path to the main BMI configuration file with
73 the "bmi_config_file" option, like this:
8ff3788c 74
ee161e8f 75 bmi_config_file = /opt/brightmail/etc/brightmail.cfg
8ff3788c 76
3ec3e3bb 77 This must go into section 1 of Exim's configuration file (You
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78 can put it right on top). If you omit this option, it
79 defaults to /opt/brightmail/etc/brightmail.cfg.
80
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.
8ff3788c 84
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85
863) Set up ACL control statement
87
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
3ec3e3bb 96 the "accept" blocks from Exim's default configuration file:
8ff3788c 97
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98
99 accept domains = +local_domains
100 endpass
101 verify = recipient
102 control = bmi_run
103
104 accept domains = +relay_to_domains
105 endpass
106 verify = recipient
107 control = bmi_run
8ff3788c 108
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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.
111
112
1134) Setting up routers to use BMI verdicts
114
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
3ec3e3bb 119 at that stage. From Exim's view, a verdict can have the
ee161e8f 120 following outcomes:
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122 o deliver the message normally
123 o deliver the message to an alternate location
124 o do not deliver the message
8ff3788c 125
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126 To query the verdict for a recipient, the implementation
127 offers the following tools:
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128
129
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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:
8ff3788c 134
ee161e8f 135 o bmi_deliver_default
8ff3788c 136
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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.
8ff3788c 141
ee161e8f 142 o bmi_deliver_alternate
8ff3788c 143
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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.
8ff3788c 150
ee161e8f 151 o bmi_dont_deliver
8ff3788c 152
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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:
8ff3788c 157
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158 # don't deliver messages handled by the BMI server
159 bmi_blackhole:
160 driver = redirect
161 bmi_dont_deliver
162 data = :blackhole:
8ff3788c 163
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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.
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168
169
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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:
8ff3788c 175
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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
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181
182
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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:
8ff3788c 187
ee161e8f 188 o $bmi_base64_verdict
8ff3788c 189
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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:
8ff3788c 193
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194 localuser:
195 driver = accept
196 check_local_user
197 headers_add = X-Brightmail-Verdict: $bmi_base64_verdict
198 transport = local_delivery
8ff3788c 199
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200 If there is no verdict available for the recipient being
201 routed, this variable contains the empty string.
8ff3788c 202
ee161e8f 203 o $bmi_base64_tracker_verdict
8ff3788c 204
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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:
8ff3788c 209
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210 localuser:
211 driver = accept
212 check_local_user
213 headers_add = X-Brightmail-Tracker: $bmi_base64_tracker_verdict
214 transport = local_delivery
8ff3788c 215
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216 If there is no verdict available for the recipient being
217 routed, this variable contains the empty string.
8ff3788c 218
ee161e8f 219 o $bmi_alt_location
8ff3788c 220
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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.
8ff3788c 229
ee161e8f 230 o $bmi_deliver
8ff3788c 231
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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.
8ff3788c 235
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236 $bmi_deliver is '0': the message should NOT be delivered.
237 $bmi_deliver is '1': the message should be delivered.
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238
239
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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.
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248
249
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2505) Using per-recipient opt-in information (Optional)
251
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
3ec3e3bb 257 already look up recipient data in Exim anyway (which can
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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'.
8ff3788c 269
ee161e8f 270 The file format:
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272 user1@mydomain.com: <OPTIN STRING1>:<OPTIN STRING2>
273 user2@thatdomain.com: <OPTIN STRING3>
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274
275
ee161e8f 276 The example:
8ff3788c 277
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278 accept domains = +relay_to_domains
279 endpass
280 verify = recipient
281 bmi_optin = ${lookup{$local_part@$domain}lsearch{/etc/exim/bmi_optin_data}}
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282 control = bmi_run
283
ee161e8f 284 Of course, you can also use any other lookup method that
3ec3e3bb 285 Exim supports, including LDAP, Postgres, MySQL, Oracle etc.,
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286 as long as the result is a list of colon-separated opt-in
287 strings.
8ff3788c 288
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289 For a list of available opt-in strings, please contact your
290 Brightmail representative.
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292
293
294
0b23848a 295SRS (Sender Rewriting Scheme) Support
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296--------------------------------------------------------------
297
298Exiscan currently includes SRS support via Miles Wilton's
8ff3788c 299libsrs_alt library. The current version of the supported
f413521a 300library is 0.5, there are reports of 1.0 working.
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301
302In order to use SRS, you must get a copy of libsrs_alt from
303
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304https://opsec.eu/src/srs/
305
306(not the original source, which has disappeared.)
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307
308Unpack the tarball, then refer to MTAs/README.EXIM
309to proceed. You need to set
310
311EXPERIMENTAL_SRS=yes
312
313in your Local/Makefile.
314
315
f413521a 316
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317DCC Support
318--------------------------------------------------------------
d36254f2 319Distributed Checksum Clearinghouse; http://www.rhyolite.com/dcc/
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320
321*) Building exim
322
323In order to build exim with DCC support add
324
325EXPERIMENTAL_DCC=yes
326
327to your Makefile. (Re-)build/install exim. exim -d should show
328EXPERIMENTAL_DCC under "Support for".
329
330
331*) Configuration
332
333In the main section of exim.cf add at least
334 dccifd_address = /usr/local/dcc/var/dccifd
335or
336 dccifd_address = <ip> <port>
337
338In the DATA ACL you can use the new condition
339 dcc = *
340
341After that "$dcc_header" contains the X-DCC-Header.
342
d36a0501 343Return values are:
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344 fail for overall "R", "G" from dccifd
345 defer for overall "T" from dccifd
346 accept for overall "A", "S" from dccifd
347
348dcc = */defer_ok works as for spamd.
349
350The "$dcc_result" variable contains the overall result from DCC
351answer. There will an X-DCC: header added to the mail.
352
353Usually you'll use
354 defer !dcc = *
355to greylist with DCC.
356
357If you set, in the main section,
358 dcc_direct_add_header = true
359then the dcc header will be added "in deep" and if the spool
360file was already written it gets removed. This forces Exim to
361write it again if needed. This helps to get the DCC Header
362through to eg. SpamAssassin.
363
364If you want to pass even more headers in the middle of the
365DATA stage you can set
366 $acl_m_dcc_add_header
05c39afa 367to tell the DCC routines to add more information; eg, you might set
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368this to some results from ClamAV. Be careful. Header syntax is
369not checked and is added "as is".
370
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371In case you've troubles with sites sending the same queue items from several
372hosts and fail to get through greylisting you can use
373$acl_m_dcc_override_client_ip
374
375Setting $acl_m_dcc_override_client_ip to an IP address overrides the default
376of $sender_host_address. eg. use the following ACL in DATA stage:
377
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
383
384Then set something like
385# cat /etc/mail/multipleip_sites
386mout-xforward.gmx.net 82.165.159.12
387mout.gmx.net 212.227.15.16
388
4c04137d 389Use a reasonable IP. eg. one the sending cluster actually uses.
0e1ccf44 390
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391
392
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393DMARC Support
394--------------------------------------------------------------
395
396DMARC combines feedback from SPF, DKIM, and header From: in order
397to attempt to provide better indicators of the authenticity of an
398email. This document does not explain the fundamentals, you
399should read and understand how it works by visiting the website at
400http://www.dmarc.org/.
401
402DMARC support is added via the libopendmarc library. Visit:
403
404 http://sourceforge.net/projects/opendmarc/
405
406to obtain a copy, or find it in your favorite rpm package
407repository. If building from source, this description assumes
408that headers will be in /usr/local/include, and that the libraries
409are in /usr/local/lib.
410
4111. To compile Exim with DMARC support, you must first enable SPF.
48155ab3 412Please read the Local/Makefile comments on enabling the SUPPORT_SPF
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413feature. You must also have DKIM support, so you cannot set the
414DISABLE_DKIM feature. Once both of those conditions have been met
415you can enable DMARC in Local/Makefile:
416
417EXPERIMENTAL_DMARC=yes
418LDFLAGS += -lopendmarc
419# CFLAGS += -I/usr/local/include
420# LDFLAGS += -L/usr/local/lib
421
422The first line sets the feature to include the correct code, and
423the second line says to link the libopendmarc libraries into the
424exim binary. The commented out lines should be uncommented if you
425built opendmarc from source and installed in the default location.
426Adjust the paths if you installed them elsewhere, but you do not
427need to uncomment them if an rpm (or you) installed them in the
428package controlled locations (/usr/include and /usr/lib).
429
430
4312. Use the following global settings to configure DMARC:
432
d7b5f2ab 433Required:
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434dmarc_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/.
ddd16464 439 See also util/renew-opendmarc-tlds.sh script.
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440
441Optional:
442dmarc_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.
449
5455f548 450dmarc_forensic_sender Alternate email address to use when sending a
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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.
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454
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.
461
462 Default: unset.
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463
464
4653. By default, the DMARC processing will run for any remote,
466non-authenticated user. It makes sense to only verify DMARC
467status of messages coming from remote, untrusted sources. You can
468use standard conditions such as hosts, senders, etc, to decide that
469DMARC verification should *not* be performed for them and disable
470DMARC with a control setting:
471
12d0043d 472 control = dmarc_disable_verify
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473
474A DMARC record can also specify a "forensic address", which gives
475exim an email address to submit reports about failed alignment.
476Exim does not do this by default because in certain conditions it
477results in unintended information leakage (what lists a user might
478be subscribed to, etc). You must configure exim to submit forensic
479reports to the owner of the domain. If the DMARC record contains a
480forensic address and you specify the control statement below, then
481exim will send these forensic emails. It's also advised that you
482configure a dmarc_forensic_sender because the default sender address
483construction might be inadequate.
484
7b2f71c1 485 control = dmarc_enable_forensic
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486
487(AGAIN: You can choose not to send these forensic reports by simply
7b2f71c1 488not putting the dmarc_enable_forensic control line at any point in
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489your exim config. If you don't tell it to send them, it will not
490send them.)
491
492There are no options to either control. Both must appear before
493the DATA acl.
494
495
4964. 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
498call the spf condition first in the ACLs, then the "dmarc_status"
499condition. Putting this condition in the ACLs is required in order
500for a DMARC check to actually occur. All of the variables are set
501up before the DATA ACL, but there is no actual DMARC check that
502occurs until a "dmarc_status" condition is encountered in the ACLs.
503
504The dmarc_status condition takes a list of strings on its
505right-hand side. These strings describe recommended action based
506on the DMARC check. To understand what the policy recommendations
507mean, refer to the DMARC website above. Valid strings are:
508
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.
7a8678e6 515 o none The DMARC check passed and the library recommends
516 no specific action, neutral.
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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.
7a8678e6 520 o temperror Library error or dns error.
05070e30 521 o off The DMARC check was disabled for this email.
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522
523You can prefix each string with an exclamation mark to invert its
524meaning, for example "!accept" will match all results but
525"accept". The string list is evaluated left-to-right in a
526short-circuit fashion. When a string matches the outcome of the
527DMARC check, the condition succeeds. If none of the listed
528strings matches the outcome of the DMARC check, the condition
529fails.
530
531Of course, you can also use any other lookup method that Exim
532supports, including LDAP, Postgres, MySQL, etc, as long as the
8c8b8274 533result is a list of colon-separated strings.
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535Performing the check sets up information used by the
536${authresults } expansion item.
537
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538Several expansion variables are set before the DATA ACL is
539processed, and you can use them in this ACL. The following
540expansion variables are available:
541
542 o $dmarc_status
543 This is a one word status indicating what the DMARC library
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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.
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548
549 o $dmarc_status_text
550 This is a slightly longer, human readable status.
551
552 o $dmarc_used_domain
553 This is the domain which DMARC used to look up the DMARC
554 policy record.
555
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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.
560
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561A now-redundant variable $dmarc_ar_header has now been withdrawn.
562Use the ${authresults } expansion instead.
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563
564
5655. How to enable DMARC advanced operation:
566By default, Exim's DMARC configuration is intended to be
567non-intrusive and conservative. To facilitate this, Exim will not
568create any type of logging files without explicit configuration by
569you, the admin. Nor will Exim send out any emails/reports about
570DMARC issues without explicit configuration by you, the admin (other
571than typical bounce messages that may come about due to ACL
572processing or failure delivery issues).
573
574In order to log statistics suitable to be imported by the opendmarc
575tools, you need to:
576a. Configure the global setting dmarc_history_file.
577b. Configure cron jobs to call the appropriate opendmarc history
578 import scripts and truncating the dmarc_history_file.
579
580In order to send forensic reports, you need to:
581a. Configure the global setting dmarc_forensic_sender.
582b. Configure, somewhere before the DATA ACL, the control option to
583 enable sending DMARC forensic reports.
584
585
5866. Example usage:
587(RCPT ACL)
588 warn domains = +local_domains
589 hosts = +local_hosts
12d0043d 590 control = dmarc_disable_verify
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591
592 warn !domains = +screwed_up_dmarc_records
593 control = dmarc_enable_forensic
594
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595 warn condition = (lookup if destined to mailing list)
596 set acl_m_mailing_list = 1
597
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598(DATA ACL)
599 warn dmarc_status = accept : none : off
600 !authenticated = *
601 log_message = DMARC DEBUG: $dmarc_status $dmarc_used_domain
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602
603 warn dmarc_status = !accept
604 !authenticated = *
605 log_message = DMARC DEBUG: '$dmarc_status' for $dmarc_used_domain
606
607 warn dmarc_status = quarantine
608 !authenticated = *
609 set $acl_m_quarantine = 1
610 # Do something in a transport with this flag variable
611
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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
615
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616 deny dmarc_status = reject
617 !authenticated = *
7b2f71c1 618 message = Message from $dmarc_used_domain failed sender's DMARC policy, REJECT
1899bab2 619
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620 warn add_header = :at_start:${authresults {$primary_hostname}}
621
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622
623
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624DSN extra information
625---------------------
626If compiled with EXPERIMENTAL_DSN_INFO extra information will be added
627to DSN fail messages ("bounces"), when available. The intent is to aid
628tracing of specific failing messages, when presented with a "bounce"
629complaint and needing to search logs.
630
631
632The remote MTA IP address, with port number if nonstandard.
633Example:
634 Remote-MTA: X-ip; [127.0.0.1]:587
635Rationale:
636 Several addresses may correspond to the (already available)
637 dns name for the remote MTA.
638
639The remote MTA connect-time greeting.
640Example:
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
642Rationale:
643 This string sometimes presents the remote MTA's idea of its
644 own name, and sometimes identifies the MTA software.
645
646The remote MTA response to HELO or EHLO.
647Example:
648 X-Remote-MTA-helo-response: X-str; 250-the.local.host.name Hello localhost [127.0.0.1]
649Limitations:
650 Only the first line of a multiline response is recorded.
651Rationale:
652 This string sometimes presents the remote MTA's view of
653 the peer IP connecting to it.
654
655The reporting MTA detailed diagnostic.
656Example:
657 X-Exim-Diagnostic: X-str; SMTP error from remote mail server after RCPT TO:<d3@myhost.test.ex>: 550 hard error
658Rationale:
4c04137d 659 This string sometimes give extra information over the
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660 existing (already available) Diagnostic-Code field.
661
662
663Note that non-RFC-documented field names and data types are used.
664
665
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666LMDB Lookup support
667-------------------
668LMDB is an ultra-fast, ultra-compact, crash-proof key-value embedded data store.
4c04137d 669It is modeled loosely on the BerkeleyDB API. You should read about the feature
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670set as well as operation modes at https://symas.com/products/lightning-memory-mapped-database/
671
672LMDB single key lookup support is provided by linking to the LMDB C library.
673The current implementation does not support writing to the LMDB database.
674
675Visit https://github.com/LMDB/lmdb to download the library or find it in your
676operating systems package repository.
677
678If building from source, this description assumes that headers will be in
679/usr/local/include, and that the libraries are in /usr/local/lib.
680
6811. In order to build exim with LMDB lookup support add or uncomment
682
683EXPERIMENTAL_LMDB=yes
684
685to your Local/Makefile. (Re-)build/install exim. exim -d should show
686Experimental_LMDB in the line "Support for:".
687
688EXPERIMENTAL_LMDB=yes
689LDFLAGS += -llmdb
690# CFLAGS += -I/usr/local/include
691# LDFLAGS += -L/usr/local/lib
692
693The first line sets the feature to include the correct code, and
694the second line says to link the LMDB libraries into the
695exim binary. The commented out lines should be uncommented if you
696built LMDB from source and installed in the default location.
697Adjust the paths if you installed them elsewhere, but you do not
698need to uncomment them if an rpm (or you) installed them in the
699package controlled locations (/usr/include and /usr/lib).
700
7012. Create your LMDB files, you can use the mdb_load utility which is
702part of the LMDB distribution our your favourite language bindings.
703
7043. Add the single key lookups to your exim.conf file, example lookups
705are below.
706
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}}
895fbaf2 710
ed0512a1 711
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712Queuefile transport
713-------------------
714Queuefile is a pseudo transport which does not perform final delivery.
715It simply copies the exim spool files out of the spool directory into
716an external directory retaining the exim spool format.
717
718The spool files can then be processed by external processes and then
719requeued into exim spool directories for final delivery.
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720However, note carefully the warnings in the main documentation on
721qpool file formats.
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722
723The motivation/inspiration for the transport is to allow external
724processes to access email queued by exim and have access to all the
725information which would not be available if the messages were delivered
726to the process in the standard email formats.
727
728The mailscanner package is one of the processes that can take advantage
729of this transport to filter email.
730
731The transport can be used in the same way as the other existing transports,
732i.e by configuring a router to route mail to a transport configured with
733the queuefile driver.
734
735The transport only takes one option:
736
737* directory - This is used to specify the directory messages should be
9604413b 738copied to. Expanded.
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739
740The generic transport options (body_only, current_directory, disable_logging,
741debug_print, delivery_date_add, envelope_to_add, event_action, group,
742headers_add, headers_only, headers_remove, headers_rewrite, home_directory,
743initgroups, max_parallel, message_size_limit, rcpt_include_affixes,
744retry_use_local_part, return_path, return_path_add, shadow_condition,
745shadow_transport, transport_filter, transport_filter_timeout, user) are
746ignored.
747
748Sample configuration:
749
750(Router)
751
752scan:
753 driver = accept
754 transport = scan
755
756(Transport)
757
758scan:
759 driver = queuefile
760 directory = /var/spool/baruwa-scanner/input
761
762
763In order to build exim with Queuefile transport support add or uncomment
764
765EXPERIMENTAL_QUEUEFILE=yes
766
767to your Local/Makefile. (Re-)build/install exim. exim -d should show
768Experimental_QUEUEFILE in the line "Support for:".
769
770
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771ARC support
772-----------
773Specification: https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-11
774Note that this is not an RFC yet, so may change.
775
776ARC is intended to support the utility of SPF and DKIM in the presence of
777intermediaries in the transmission path - forwarders and mailinglists -
778by establishing a cryptographically-signed chain in headers.
779
780Normally one would only bother doing ARC-signing when functioning as
781an intermediary. One might do verify for local destinations.
782
783ARC uses the notion of a "ADministrative Management Domain" (ADMD).
784Described in RFC 5598 (section 2.3), this is essentially the set of
785mail-handling systems that the mail transits. A label should be chosen to
786identify the ADMD. Messages should be ARC-verified on entry to the ADMD,
787and ARC-signed on exit from it.
788
789
790Verification
791--
792An ACL condition is provided to perform the "verifier actions" detailed
793in section 6 of the above specification. It may be called from the DATA ACL
794and succeeds if the result matches any of a given list.
795It also records the highest ARC instance number (the chain size)
796and verification result for later use in creating an Authentication-Results:
797standard header.
798
799 verify = arc/<acceptable_list> none:fail:pass
800
801 add_header = :at_start:${authresults {<admd-identifier>}}
802
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>.
805
a1d4300b 806There are four new variables:
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807
808 $arc_state One of pass, fail, none
809 $arc_state_reason (if fail, why)
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810 $arc_domains colon-sep list of ARC chain domains, in chain order.
811 problematic elements may have empty list elements
ea7b1f16 812 $arc_oldest_pass lowest passing instance number of chain
93c931f8 813
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814Example:
815 logwrite = oldest-p-ams: <${reduce {$lh_ARC-Authentication-Results:} \
816 {} \
817 {${if = {$arc_oldest_pass} \
818 {${extract {i}{${extract {1}{;}{$item}}}}} \
819 {$item} {$value}}} \
820 }>
821
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822Receive log lines for an ARC pass will be tagged "ARC".
823
824
825Signing
826--
a93dbf44 827arc_sign = <admd-identifier> : <selector> : <privkey> [ : <options> ]
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828An option on the smtp transport, which constructs and prepends to the message
829an ARC set of headers. The textually-first Authentication-Results: header
830is used as a basis (you must have added one on entry to the ADMD).
9f7d9fa1 831Expanded as a whole; if unset, empty or forced-failure then no signing is done.
5054c4fd 832If it is set, all of the first three elements must be non-empty.
617d3932 833
a93dbf44 834The fourth element is optional, and if present consists of a comma-separated list
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835of options. The options implemented are
836
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.
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844
845[As of writing, gmail insist that a t= tag on the AS is mandatory]
846
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847Caveats:
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.
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851
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).
855
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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.
5054c4fd 862
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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.
866
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867Signing is not compatible with cutthrough delivery; any (before expansion)
868value set for the option will result in cutthrough delivery not being
869used via the transport in question.
870
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871
872
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873
874REQUIRETLS support
875------------------
876Ref: https://tools.ietf.org/html/draft-ietf-uta-smtp-require-tls-03
877
878If compiled with EXPERIMENTAL_REQUIRETLS support is included for this
879feature, where a REQUIRETLS option is added to the MAIL command.
880The client may not retry in clear if the MAIL+REQUIRETLS fails (or was never
881offered), and the server accepts an obligation that any onward transmission
882by SMTP of the messages accepted will also use REQUIRETLS - or generate a
883fail DSN.
884
885The 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"
891
892Differences from spec:
893- we support upgrading the requirement for REQUIRETLS, including adding
f9d4bb1a 894 it from cold, within an MTA. The spec only define the sourcing MUA
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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
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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]
8ac90765 901
f9d4bb1a 902Note that REQUIRETLS is only advertised once a TLS connection is achieved
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903(in contrast to STARTTLS). If you want to check the advertising, do something
904like "swaks -s 127.0.0.1 -tls -q HELO".
905
906
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907--------------------------------------------------------------
908End of file
909--------------------------------------------------------------