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7bafa7d9 TK |
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 | |
d36a0501 PP |
5 | about experimental features, all of which are unstable and |
6 | liable to incompatible change. | |
ee161e8f PH |
7 | |
8 | ||
4c04137d | 9 | Brightmail AntiSpam (BMI) support |
ee161e8f PH |
10 | -------------------------------------------------------------- |
11 | ||
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. | |
16 | ||
17 | ||
18 | 0) BMI concept and implementation overview | |
19 | ||
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: | |
31 | ||
32 | 1) Compile Exim with BMI support | |
3ec3e3bb | 33 | 2) Set up main BMI options (top section of Exim config file) |
ee161e8f PH |
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 | 40 | These four steps are explained in more details below. |
ee161e8f PH |
41 | |
42 | 1) 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 |
ee161e8f PH |
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 | |
ee161e8f PH |
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 |
ee161e8f PH |
59 | to the EXTRALIBS_EXIM line. Users of 5.5x do not need to do |
60 | this. | |
8ff3788c | 61 | |
ee161e8f PH |
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 | 69 | 2) Setting up BMI support in the Exim main configuration |
ee161e8f | 70 | |
3ec3e3bb | 71 | To enable BMI support in the main Exim configuration, you |
ee161e8f PH |
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 |
ee161e8f PH |
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 | |
ee161e8f PH |
85 | |
86 | 3) 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 | |
ee161e8f PH |
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 | |
ee161e8f PH |
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 | ||
113 | 4) 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: |
8ff3788c | 121 | |
ee161e8f PH |
122 | o deliver the message normally |
123 | o deliver the message to an alternate location | |
124 | o do not deliver the message | |
8ff3788c | 125 | |
ee161e8f PH |
126 | To query the verdict for a recipient, the implementation |
127 | offers the following tools: | |
8ff3788c TK |
128 | |
129 | ||
ee161e8f PH |
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 | |
ee161e8f PH |
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 | |
ee161e8f PH |
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 | |
ee161e8f PH |
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 | |
ee161e8f PH |
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 | |
ee161e8f PH |
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. | |
8ff3788c TK |
168 | |
169 | ||
ee161e8f PH |
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 | |
ee161e8f PH |
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 | |
8ff3788c TK |
181 | |
182 | ||
ee161e8f PH |
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 | |
ee161e8f PH |
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 | |
ee161e8f PH |
194 | localuser: |
195 | driver = accept | |
196 | check_local_user | |
197 | headers_add = X-Brightmail-Verdict: $bmi_base64_verdict | |
198 | transport = local_delivery | |
8ff3788c | 199 | |
ee161e8f PH |
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 | |
ee161e8f PH |
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 | |
ee161e8f PH |
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 | |
ee161e8f PH |
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 | |
ee161e8f PH |
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 | |
ee161e8f PH |
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 | |
ee161e8f PH |
236 | $bmi_deliver is '0': the message should NOT be delivered. |
237 | $bmi_deliver is '1': the message should be delivered. | |
8ff3788c TK |
238 | |
239 | ||
ee161e8f PH |
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. | |
8ff3788c TK |
248 | |
249 | ||
ee161e8f PH |
250 | 5) 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 |
ee161e8f PH |
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: |
8ff3788c | 271 | |
ee161e8f PH |
272 | user1@mydomain.com: <OPTIN STRING1>:<OPTIN STRING2> |
273 | user2@thatdomain.com: <OPTIN STRING3> | |
8ff3788c TK |
274 | |
275 | ||
ee161e8f | 276 | The example: |
8ff3788c | 277 | |
ee161e8f PH |
278 | accept domains = +relay_to_domains |
279 | endpass | |
280 | verify = recipient | |
281 | bmi_optin = ${lookup{$local_part@$domain}lsearch{/etc/exim/bmi_optin_data}} | |
8ff3788c TK |
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., |
ee161e8f PH |
286 | as long as the result is a list of colon-separated opt-in |
287 | strings. | |
8ff3788c | 288 | |
ee161e8f PH |
289 | For a list of available opt-in strings, please contact your |
290 | Brightmail representative. | |
ee161e8f | 291 | |
8ff3788c TK |
292 | |
293 | ||
294 | ||
0b23848a | 295 | SRS (Sender Rewriting Scheme) Support |
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296 | -------------------------------------------------------------- |
297 | ||
298 | Exiscan currently includes SRS support via Miles Wilton's | |
8ff3788c | 299 | libsrs_alt library. The current version of the supported |
f413521a | 300 | library is 0.5, there are reports of 1.0 working. |
ee161e8f PH |
301 | |
302 | In order to use SRS, you must get a copy of libsrs_alt from | |
303 | ||
f413521a PP |
304 | https://opsec.eu/src/srs/ |
305 | ||
306 | (not the original source, which has disappeared.) | |
ee161e8f PH |
307 | |
308 | Unpack the tarball, then refer to MTAs/README.EXIM | |
309 | to proceed. You need to set | |
310 | ||
311 | EXPERIMENTAL_SRS=yes | |
312 | ||
313 | in your Local/Makefile. | |
314 | ||
315 | ||
f413521a | 316 | |
0e1ccf44 PP |
317 | DCC Support |
318 | -------------------------------------------------------------- | |
d36254f2 | 319 | Distributed Checksum Clearinghouse; http://www.rhyolite.com/dcc/ |
0e1ccf44 PP |
320 | |
321 | *) Building exim | |
322 | ||
323 | In order to build exim with DCC support add | |
324 | ||
325 | EXPERIMENTAL_DCC=yes | |
326 | ||
327 | to your Makefile. (Re-)build/install exim. exim -d should show | |
328 | EXPERIMENTAL_DCC under "Support for". | |
329 | ||
330 | ||
331 | *) Configuration | |
332 | ||
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> | |
337 | ||
338 | In the DATA ACL you can use the new condition | |
339 | dcc = * | |
340 | ||
341 | After that "$dcc_header" contains the X-DCC-Header. | |
342 | ||
d36a0501 | 343 | Return values are: |
0e1ccf44 PP |
344 | fail for overall "R", "G" from dccifd |
345 | defer for overall "T" from dccifd | |
346 | accept for overall "A", "S" from dccifd | |
347 | ||
348 | dcc = */defer_ok works as for spamd. | |
349 | ||
350 | The "$dcc_result" variable contains the overall result from DCC | |
351 | answer. There will an X-DCC: header added to the mail. | |
352 | ||
353 | Usually you'll use | |
354 | defer !dcc = * | |
355 | to greylist with DCC. | |
356 | ||
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. | |
363 | ||
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 | |
05c39afa | 367 | to tell the DCC routines to add more information; eg, you might set |
0e1ccf44 PP |
368 | this to some results from ClamAV. Be careful. Header syntax is |
369 | not checked and is added "as is". | |
370 | ||
05c39afa JH |
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 | |
374 | ||
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: | |
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 | ||
384 | Then set something like | |
385 | # cat /etc/mail/multipleip_sites | |
386 | mout-xforward.gmx.net 82.165.159.12 | |
387 | mout.gmx.net 212.227.15.16 | |
388 | ||
4c04137d | 389 | Use a reasonable IP. eg. one the sending cluster actually uses. |
0e1ccf44 | 390 | |
48155ab3 JH |
391 | |
392 | ||
1899bab2 TL |
393 | DMARC Support |
394 | -------------------------------------------------------------- | |
395 | ||
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/. | |
401 | ||
402 | DMARC support is added via the libopendmarc library. Visit: | |
403 | ||
404 | http://sourceforge.net/projects/opendmarc/ | |
405 | ||
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. | |
410 | ||
411 | 1. To compile Exim with DMARC support, you must first enable SPF. | |
48155ab3 | 412 | Please read the Local/Makefile comments on enabling the SUPPORT_SPF |
1899bab2 TL |
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: | |
416 | ||
417 | EXPERIMENTAL_DMARC=yes | |
418 | LDFLAGS += -lopendmarc | |
419 | # CFLAGS += -I/usr/local/include | |
420 | # LDFLAGS += -L/usr/local/lib | |
421 | ||
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). | |
429 | ||
430 | ||
590fd9ee | 431 | 2. Use the following global options to configure DMARC: |
1899bab2 | 432 | |
d7b5f2ab | 433 | Required: |
1899bab2 TL |
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/. | |
ddd16464 | 439 | See also util/renew-opendmarc-tlds.sh script. |
590fd9ee JH |
440 | The default for the option is currently |
441 | /etc/exim/opendmarc.tlds | |
1899bab2 TL |
442 | |
443 | Optional: | |
444 | dmarc_history_file Defines the location of a file to log results | |
445 | of dmarc verification on inbound emails. The | |
446 | contents are importable by the opendmarc tools | |
447 | which will manage the data, send out DMARC | |
448 | reports, and expire the data. Make sure the | |
449 | directory of this file is writable by the user | |
450 | exim runs as. | |
451 | ||
5455f548 | 452 | dmarc_forensic_sender Alternate email address to use when sending a |
1899bab2 TL |
453 | forensic report detailing alignment failures |
454 | if a sender domain's dmarc record specifies it | |
455 | and you have configured Exim to send them. | |
5455f548 JH |
456 | |
457 | If set, this is expanded and used for the | |
458 | From: header line; the address is extracted | |
459 | from it and used for the envelope from. | |
460 | If not set, the From: header is expanded from | |
461 | the dsn_from option, and <> is used for the | |
462 | envelope from. | |
463 | ||
464 | Default: unset. | |
1899bab2 TL |
465 | |
466 | ||
467 | 3. By default, the DMARC processing will run for any remote, | |
468 | non-authenticated user. It makes sense to only verify DMARC | |
469 | status of messages coming from remote, untrusted sources. You can | |
470 | use standard conditions such as hosts, senders, etc, to decide that | |
471 | DMARC verification should *not* be performed for them and disable | |
472 | DMARC with a control setting: | |
473 | ||
12d0043d | 474 | control = dmarc_disable_verify |
1899bab2 TL |
475 | |
476 | A DMARC record can also specify a "forensic address", which gives | |
477 | exim an email address to submit reports about failed alignment. | |
478 | Exim does not do this by default because in certain conditions it | |
479 | results in unintended information leakage (what lists a user might | |
480 | be subscribed to, etc). You must configure exim to submit forensic | |
481 | reports to the owner of the domain. If the DMARC record contains a | |
482 | forensic address and you specify the control statement below, then | |
483 | exim will send these forensic emails. It's also advised that you | |
484 | configure a dmarc_forensic_sender because the default sender address | |
485 | construction might be inadequate. | |
486 | ||
7b2f71c1 | 487 | control = dmarc_enable_forensic |
1899bab2 TL |
488 | |
489 | (AGAIN: You can choose not to send these forensic reports by simply | |
7b2f71c1 | 490 | not putting the dmarc_enable_forensic control line at any point in |
1899bab2 TL |
491 | your exim config. If you don't tell it to send them, it will not |
492 | send them.) | |
493 | ||
494 | There are no options to either control. Both must appear before | |
495 | the DATA acl. | |
496 | ||
497 | ||
498 | 4. You can now run DMARC checks in incoming SMTP by using the | |
499 | "dmarc_status" ACL condition in the DATA ACL. You are required to | |
500 | call the spf condition first in the ACLs, then the "dmarc_status" | |
501 | condition. Putting this condition in the ACLs is required in order | |
502 | for a DMARC check to actually occur. All of the variables are set | |
503 | up before the DATA ACL, but there is no actual DMARC check that | |
504 | occurs until a "dmarc_status" condition is encountered in the ACLs. | |
505 | ||
506 | The dmarc_status condition takes a list of strings on its | |
507 | right-hand side. These strings describe recommended action based | |
508 | on the DMARC check. To understand what the policy recommendations | |
509 | mean, refer to the DMARC website above. Valid strings are: | |
510 | ||
511 | o accept The DMARC check passed and the library recommends | |
512 | accepting the email. | |
513 | o reject The DMARC check failed and the library recommends | |
514 | rejecting the email. | |
515 | o quarantine The DMARC check failed and the library recommends | |
516 | keeping it for further inspection. | |
7a8678e6 | 517 | o none The DMARC check passed and the library recommends |
518 | no specific action, neutral. | |
1899bab2 TL |
519 | o norecord No policy section in the DMARC record for this |
520 | sender domain. | |
521 | o nofrom Unable to determine the domain of the sender. | |
7a8678e6 | 522 | o temperror Library error or dns error. |
05070e30 | 523 | o off The DMARC check was disabled for this email. |
1899bab2 TL |
524 | |
525 | You can prefix each string with an exclamation mark to invert its | |
526 | meaning, for example "!accept" will match all results but | |
527 | "accept". The string list is evaluated left-to-right in a | |
528 | short-circuit fashion. When a string matches the outcome of the | |
529 | DMARC check, the condition succeeds. If none of the listed | |
530 | strings matches the outcome of the DMARC check, the condition | |
531 | fails. | |
532 | ||
533 | Of course, you can also use any other lookup method that Exim | |
534 | supports, including LDAP, Postgres, MySQL, etc, as long as the | |
8c8b8274 | 535 | result is a list of colon-separated strings. |
1899bab2 | 536 | |
b8444b38 JH |
537 | Performing the check sets up information used by the |
538 | ${authresults } expansion item. | |
539 | ||
1899bab2 TL |
540 | Several expansion variables are set before the DATA ACL is |
541 | processed, and you can use them in this ACL. The following | |
542 | expansion variables are available: | |
543 | ||
544 | o $dmarc_status | |
545 | This is a one word status indicating what the DMARC library | |
8c8b8274 TL |
546 | thinks of the email. It is a combination of the results of |
547 | DMARC record lookup and the SPF/DKIM/DMARC processing results | |
548 | (if a DMARC record was found). The actual policy declared | |
549 | in the DMARC record is in a separate expansion variable. | |
1899bab2 TL |
550 | |
551 | o $dmarc_status_text | |
552 | This is a slightly longer, human readable status. | |
553 | ||
554 | o $dmarc_used_domain | |
555 | This is the domain which DMARC used to look up the DMARC | |
556 | policy record. | |
557 | ||
8c8b8274 TL |
558 | o $dmarc_domain_policy |
559 | This is the policy declared in the DMARC record. Valid values | |
560 | are "none", "reject" and "quarantine". It is blank when there | |
561 | is any error, including no DMARC record. | |
562 | ||
c9cf9ac4 JH |
563 | A now-redundant variable $dmarc_ar_header has now been withdrawn. |
564 | Use the ${authresults } expansion instead. | |
1899bab2 TL |
565 | |
566 | ||
567 | 5. How to enable DMARC advanced operation: | |
568 | By default, Exim's DMARC configuration is intended to be | |
569 | non-intrusive and conservative. To facilitate this, Exim will not | |
570 | create any type of logging files without explicit configuration by | |
571 | you, the admin. Nor will Exim send out any emails/reports about | |
572 | DMARC issues without explicit configuration by you, the admin (other | |
573 | than typical bounce messages that may come about due to ACL | |
574 | processing or failure delivery issues). | |
575 | ||
576 | In order to log statistics suitable to be imported by the opendmarc | |
577 | tools, you need to: | |
578 | a. Configure the global setting dmarc_history_file. | |
579 | b. Configure cron jobs to call the appropriate opendmarc history | |
580 | import scripts and truncating the dmarc_history_file. | |
581 | ||
582 | In order to send forensic reports, you need to: | |
583 | a. Configure the global setting dmarc_forensic_sender. | |
584 | b. Configure, somewhere before the DATA ACL, the control option to | |
585 | enable sending DMARC forensic reports. | |
586 | ||
587 | ||
588 | 6. Example usage: | |
589 | (RCPT ACL) | |
590 | warn domains = +local_domains | |
591 | hosts = +local_hosts | |
12d0043d | 592 | control = dmarc_disable_verify |
1899bab2 TL |
593 | |
594 | warn !domains = +screwed_up_dmarc_records | |
595 | control = dmarc_enable_forensic | |
596 | ||
8c8b8274 TL |
597 | warn condition = (lookup if destined to mailing list) |
598 | set acl_m_mailing_list = 1 | |
599 | ||
1899bab2 TL |
600 | (DATA ACL) |
601 | warn dmarc_status = accept : none : off | |
602 | !authenticated = * | |
603 | log_message = DMARC DEBUG: $dmarc_status $dmarc_used_domain | |
1899bab2 TL |
604 | |
605 | warn dmarc_status = !accept | |
606 | !authenticated = * | |
607 | log_message = DMARC DEBUG: '$dmarc_status' for $dmarc_used_domain | |
608 | ||
609 | warn dmarc_status = quarantine | |
610 | !authenticated = * | |
611 | set $acl_m_quarantine = 1 | |
612 | # Do something in a transport with this flag variable | |
613 | ||
8c8b8274 TL |
614 | deny condition = ${if eq{$dmarc_domain_policy}{reject}} |
615 | condition = ${if eq{$acl_m_mailing_list}{1}} | |
616 | message = Messages from $dmarc_used_domain break mailing lists | |
617 | ||
1899bab2 TL |
618 | deny dmarc_status = reject |
619 | !authenticated = * | |
7b2f71c1 | 620 | message = Message from $dmarc_used_domain failed sender's DMARC policy, REJECT |
1899bab2 | 621 | |
b8444b38 JH |
622 | warn add_header = :at_start:${authresults {$primary_hostname}} |
623 | ||
1899bab2 TL |
624 | |
625 | ||
895fbaf2 JH |
626 | DSN extra information |
627 | --------------------- | |
628 | If compiled with EXPERIMENTAL_DSN_INFO extra information will be added | |
629 | to DSN fail messages ("bounces"), when available. The intent is to aid | |
630 | tracing of specific failing messages, when presented with a "bounce" | |
631 | complaint and needing to search logs. | |
632 | ||
633 | ||
634 | The remote MTA IP address, with port number if nonstandard. | |
635 | Example: | |
636 | Remote-MTA: X-ip; [127.0.0.1]:587 | |
637 | Rationale: | |
638 | Several addresses may correspond to the (already available) | |
639 | dns name for the remote MTA. | |
640 | ||
641 | The remote MTA connect-time greeting. | |
642 | Example: | |
643 | X-Remote-MTA-smtp-greeting: X-str; 220 the.local.host.name ESMTP Exim x.yz Tue, 2 Mar 1999 09:44:33 +0000 | |
644 | Rationale: | |
645 | This string sometimes presents the remote MTA's idea of its | |
646 | own name, and sometimes identifies the MTA software. | |
647 | ||
648 | The remote MTA response to HELO or EHLO. | |
649 | Example: | |
650 | X-Remote-MTA-helo-response: X-str; 250-the.local.host.name Hello localhost [127.0.0.1] | |
651 | Limitations: | |
652 | Only the first line of a multiline response is recorded. | |
653 | Rationale: | |
654 | This string sometimes presents the remote MTA's view of | |
655 | the peer IP connecting to it. | |
656 | ||
657 | The reporting MTA detailed diagnostic. | |
658 | Example: | |
659 | X-Exim-Diagnostic: X-str; SMTP error from remote mail server after RCPT TO:<d3@myhost.test.ex>: 550 hard error | |
660 | Rationale: | |
4c04137d | 661 | This string sometimes give extra information over the |
895fbaf2 JH |
662 | existing (already available) Diagnostic-Code field. |
663 | ||
664 | ||
665 | Note that non-RFC-documented field names and data types are used. | |
666 | ||
667 | ||
5bde3efa ACK |
668 | LMDB Lookup support |
669 | ------------------- | |
670 | LMDB is an ultra-fast, ultra-compact, crash-proof key-value embedded data store. | |
4c04137d | 671 | It is modeled loosely on the BerkeleyDB API. You should read about the feature |
5bde3efa ACK |
672 | set as well as operation modes at https://symas.com/products/lightning-memory-mapped-database/ |
673 | ||
674 | LMDB single key lookup support is provided by linking to the LMDB C library. | |
675 | The current implementation does not support writing to the LMDB database. | |
676 | ||
677 | Visit https://github.com/LMDB/lmdb to download the library or find it in your | |
678 | operating systems package repository. | |
679 | ||
680 | If building from source, this description assumes that headers will be in | |
681 | /usr/local/include, and that the libraries are in /usr/local/lib. | |
682 | ||
683 | 1. In order to build exim with LMDB lookup support add or uncomment | |
684 | ||
685 | EXPERIMENTAL_LMDB=yes | |
686 | ||
687 | to your Local/Makefile. (Re-)build/install exim. exim -d should show | |
688 | Experimental_LMDB in the line "Support for:". | |
689 | ||
690 | EXPERIMENTAL_LMDB=yes | |
691 | LDFLAGS += -llmdb | |
692 | # CFLAGS += -I/usr/local/include | |
693 | # LDFLAGS += -L/usr/local/lib | |
694 | ||
695 | The first line sets the feature to include the correct code, and | |
696 | the second line says to link the LMDB libraries into the | |
697 | exim binary. The commented out lines should be uncommented if you | |
698 | built LMDB from source and installed in the default location. | |
699 | Adjust the paths if you installed them elsewhere, but you do not | |
700 | need to uncomment them if an rpm (or you) installed them in the | |
701 | package controlled locations (/usr/include and /usr/lib). | |
702 | ||
703 | 2. Create your LMDB files, you can use the mdb_load utility which is | |
704 | part of the LMDB distribution our your favourite language bindings. | |
705 | ||
706 | 3. Add the single key lookups to your exim.conf file, example lookups | |
707 | are below. | |
708 | ||
709 | ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}} | |
710 | ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}fail} | |
711 | ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}} | |
895fbaf2 | 712 | |
ed0512a1 | 713 | |
3369a853 ACK |
714 | Queuefile transport |
715 | ------------------- | |
716 | Queuefile is a pseudo transport which does not perform final delivery. | |
717 | It simply copies the exim spool files out of the spool directory into | |
718 | an external directory retaining the exim spool format. | |
719 | ||
720 | The spool files can then be processed by external processes and then | |
721 | requeued into exim spool directories for final delivery. | |
20751c76 JH |
722 | However, note carefully the warnings in the main documentation on |
723 | qpool file formats. | |
3369a853 ACK |
724 | |
725 | The motivation/inspiration for the transport is to allow external | |
726 | processes to access email queued by exim and have access to all the | |
727 | information which would not be available if the messages were delivered | |
728 | to the process in the standard email formats. | |
729 | ||
730 | The mailscanner package is one of the processes that can take advantage | |
731 | of this transport to filter email. | |
732 | ||
733 | The transport can be used in the same way as the other existing transports, | |
734 | i.e by configuring a router to route mail to a transport configured with | |
735 | the queuefile driver. | |
736 | ||
737 | The transport only takes one option: | |
738 | ||
739 | * directory - This is used to specify the directory messages should be | |
9604413b | 740 | copied to. Expanded. |
3369a853 ACK |
741 | |
742 | The generic transport options (body_only, current_directory, disable_logging, | |
743 | debug_print, delivery_date_add, envelope_to_add, event_action, group, | |
744 | headers_add, headers_only, headers_remove, headers_rewrite, home_directory, | |
745 | initgroups, max_parallel, message_size_limit, rcpt_include_affixes, | |
746 | retry_use_local_part, return_path, return_path_add, shadow_condition, | |
747 | shadow_transport, transport_filter, transport_filter_timeout, user) are | |
748 | ignored. | |
749 | ||
750 | Sample configuration: | |
751 | ||
752 | (Router) | |
753 | ||
754 | scan: | |
755 | driver = accept | |
756 | transport = scan | |
757 | ||
758 | (Transport) | |
759 | ||
760 | scan: | |
761 | driver = queuefile | |
762 | directory = /var/spool/baruwa-scanner/input | |
763 | ||
764 | ||
765 | In order to build exim with Queuefile transport support add or uncomment | |
766 | ||
767 | EXPERIMENTAL_QUEUEFILE=yes | |
768 | ||
769 | to your Local/Makefile. (Re-)build/install exim. exim -d should show | |
770 | Experimental_QUEUEFILE in the line "Support for:". | |
771 | ||
772 | ||
617d3932 JH |
773 | ARC support |
774 | ----------- | |
775 | Specification: https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-11 | |
776 | Note that this is not an RFC yet, so may change. | |
777 | ||
778 | ARC is intended to support the utility of SPF and DKIM in the presence of | |
779 | intermediaries in the transmission path - forwarders and mailinglists - | |
780 | by establishing a cryptographically-signed chain in headers. | |
781 | ||
782 | Normally one would only bother doing ARC-signing when functioning as | |
783 | an intermediary. One might do verify for local destinations. | |
784 | ||
785 | ARC uses the notion of a "ADministrative Management Domain" (ADMD). | |
786 | Described in RFC 5598 (section 2.3), this is essentially the set of | |
787 | mail-handling systems that the mail transits. A label should be chosen to | |
788 | identify the ADMD. Messages should be ARC-verified on entry to the ADMD, | |
789 | and ARC-signed on exit from it. | |
790 | ||
791 | ||
792 | Verification | |
793 | -- | |
794 | An ACL condition is provided to perform the "verifier actions" detailed | |
795 | in section 6 of the above specification. It may be called from the DATA ACL | |
796 | and succeeds if the result matches any of a given list. | |
797 | It also records the highest ARC instance number (the chain size) | |
798 | and verification result for later use in creating an Authentication-Results: | |
799 | standard header. | |
800 | ||
801 | verify = arc/<acceptable_list> none:fail:pass | |
802 | ||
803 | add_header = :at_start:${authresults {<admd-identifier>}} | |
804 | ||
805 | Note that it would be wise to strip incoming messages of A-R headers | |
806 | that claim to be from our own <admd-identifier>. | |
807 | ||
a1d4300b | 808 | There are four new variables: |
9cffa436 JH |
809 | |
810 | $arc_state One of pass, fail, none | |
811 | $arc_state_reason (if fail, why) | |
08bd2689 JH |
812 | $arc_domains colon-sep list of ARC chain domains, in chain order. |
813 | problematic elements may have empty list elements | |
ea7b1f16 | 814 | $arc_oldest_pass lowest passing instance number of chain |
93c931f8 | 815 | |
bce15b62 JH |
816 | Example: |
817 | logwrite = oldest-p-ams: <${reduce {$lh_ARC-Authentication-Results:} \ | |
818 | {} \ | |
819 | {${if = {$arc_oldest_pass} \ | |
820 | {${extract {i}{${extract {1}{;}{$item}}}}} \ | |
821 | {$item} {$value}}} \ | |
822 | }> | |
823 | ||
617d3932 JH |
824 | Receive log lines for an ARC pass will be tagged "ARC". |
825 | ||
826 | ||
827 | Signing | |
828 | -- | |
a93dbf44 | 829 | arc_sign = <admd-identifier> : <selector> : <privkey> [ : <options> ] |
617d3932 JH |
830 | An option on the smtp transport, which constructs and prepends to the message |
831 | an ARC set of headers. The textually-first Authentication-Results: header | |
832 | is used as a basis (you must have added one on entry to the ADMD). | |
9f7d9fa1 | 833 | Expanded as a whole; if unset, empty or forced-failure then no signing is done. |
5054c4fd | 834 | If it is set, all of the first three elements must be non-empty. |
617d3932 | 835 | |
a93dbf44 | 836 | The fourth element is optional, and if present consists of a comma-separated list |
0e83c148 JH |
837 | of options. The options implemented are |
838 | ||
839 | timestamps Add a t= tag to the generated AMS and AS headers, with the | |
840 | current time. | |
841 | expire[=<val>] Add an x= tag to the generated AMS header, with an expiry time. | |
842 | If the value <val> is an plain number it is used unchanged. | |
843 | If it starts with a '+' then the following number is added | |
844 | to the current time, as an offset in seconds. | |
845 | If a value is not given it defaults to a one month offset. | |
a93dbf44 JH |
846 | |
847 | [As of writing, gmail insist that a t= tag on the AS is mandatory] | |
848 | ||
afcdd656 PP |
849 | Caveats: |
850 | * There must be an Authentication-Results header, presumably added by an ACL | |
851 | while receiving the message, for the same ADMD, for arc_sign to succeed. | |
852 | This requires careful coordination between inbound and outbound logic. | |
5054c4fd JH |
853 | |
854 | Only one A-R header is taken account of. This is a limitation versus | |
855 | the ARC spec (which says that all A-R headers from within the ADMD must | |
856 | be used). | |
857 | ||
afcdd656 PP |
858 | * If passing a message to another system, such as a mailing-list manager |
859 | (MLM), between receipt and sending, be wary of manipulations to headers made | |
860 | by the MLM. | |
861 | + For instance, Mailman with REMOVE_DKIM_HEADERS==3 might improve | |
862 | deliverability in a pre-ARC world, but that option also renames the | |
863 | Authentication-Results header, which breaks signing. | |
5054c4fd | 864 | |
afcdd656 PP |
865 | * Even if you use multiple DKIM keys for different domains, the ARC concept |
866 | should try to stick to one ADMD, so pick a primary domain and use that for | |
867 | AR headers and outbound signing. | |
868 | ||
5add7dc4 JH |
869 | Signing is not compatible with cutthrough delivery; any (before expansion) |
870 | value set for the option will result in cutthrough delivery not being | |
871 | used via the transport in question. | |
872 | ||
617d3932 JH |
873 | |
874 | ||
8ac90765 | 875 | |
b10c87b3 JH |
876 | TLS Session Resumption |
877 | ---------------------- | |
43e2db44 | 878 | TLS Session Resumption for TLS 1.2 and TLS 1.3 connections can be used (defined |
b10c87b3 | 879 | in RFC 5077 for 1.2). The support for this can be included by building with |
43e2db44 JH |
880 | EXPERIMENTAL_TLS_RESUME defined. This requires GnuTLS 3.6.3 or OpenSSL 1.1.1 |
881 | (or later). | |
b10c87b3 JH |
882 | |
883 | Session resumption (this is the "stateless" variant) involves the server sending | |
884 | a "session ticket" to the client on one connection, which can be stored by the | |
885 | client and used for a later session. The ticket contains sufficient state for | |
886 | the server to reconstruct the TLS session, avoiding some expensive crypto | |
887 | calculation and one full packet roundtrip time. | |
888 | ||
889 | Operational cost/benefit: | |
890 | The extra data being transmitted costs a minor amount, and the client has | |
68c62739 | 891 | extra costs in storing and retrieving the data. |
b10c87b3 | 892 | |
68c62739 JH |
893 | In the Exim/Gnutls implementation the extra cost on an initial connection |
894 | which is TLS1.2 over a loopback path is about 6ms on 2017-laptop class hardware. | |
895 | The saved cost on a subsequent connection is about 4ms; three or more | |
896 | connections become a net win. On longer network paths, two or more | |
897 | connections will have an average lower startup time thanks to the one | |
898 | saved packet roundtrip. TLS1.3 will save the crypto cpu costs but not any | |
899 | packet roundtrips. | |
900 | ||
901 | Since a new hints DB is used, the hints DB maintenance should be updated | |
902 | to additionally handle "tls". | |
b10c87b3 JH |
903 | |
904 | Security aspects: | |
905 | The session ticket is encrypted, but is obviously an additional security | |
68c62739 JH |
906 | vulnarability surface. An attacker able to decrypt it would have access |
907 | all connections using the resumed session. | |
908 | The session ticket encryption key is not committed to storage by the server | |
dea4b568 JH |
909 | and is rotated regularly (OpenSSL: 1hr, and one previous key is used for |
910 | overlap; GnuTLS 6hr but does not specify any overlap). | |
911 | Tickets have limited lifetime (2hr, and new ones issued after 1hr under | |
912 | OpenSSL. GnuTLS 2hr, appears to not do overlap). | |
b10c87b3 | 913 | |
68c62739 JH |
914 | There is a question-mark over the security of the Diffie-Helman parameters |
915 | used for session negotiation. TBD. q-value; cf bug 1895 | |
b10c87b3 JH |
916 | |
917 | Observability: | |
918 | New log_selector "tls_resumption", appends an asterisk to the tls_cipher "X=" | |
68c62739 JH |
919 | element. |
920 | ||
4a1bd6b9 | 921 | Variables $tls_{in,out}_resumption have bits 0-4 indicating respectively |
68c62739 JH |
922 | support built, client requested ticket, client offered session, |
923 | server issued ticket, resume used. A suitable decode list is provided | |
924 | in the builtin macro _RESUME_DECODE for ${listextract {}{}}. | |
925 | ||
926 | Issues: | |
927 | In a resumed session: | |
11c4a22b | 928 | $tls_{in,out}_cipher will have values different to the original (under GnuTLS) |
4f1d23a1 | 929 | $tls_{in,out}_ocsp will be "not requested" or "no response", and |
f4e62a87 | 930 | hosts_require_ocsp will fail |
b10c87b3 JH |
931 | |
932 | ||
ee161e8f PH |
933 | -------------------------------------------------------------- |
934 | End of file | |
935 | -------------------------------------------------------------- |