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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 |
ee161e8f PH |
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 | |
1899bab2 TL |
391 | DMARC Support |
392 | -------------------------------------------------------------- | |
393 | ||
394 | DMARC combines feedback from SPF, DKIM, and header From: in order | |
395 | to attempt to provide better indicators of the authenticity of an | |
396 | email. This document does not explain the fundamentals, you | |
397 | should read and understand how it works by visiting the website at | |
398 | http://www.dmarc.org/. | |
399 | ||
400 | DMARC support is added via the libopendmarc library. Visit: | |
401 | ||
402 | http://sourceforge.net/projects/opendmarc/ | |
403 | ||
404 | to obtain a copy, or find it in your favorite rpm package | |
405 | repository. If building from source, this description assumes | |
406 | that headers will be in /usr/local/include, and that the libraries | |
407 | are in /usr/local/lib. | |
408 | ||
409 | 1. To compile Exim with DMARC support, you must first enable SPF. | |
410 | Please read the above section on enabling the EXPERIMENTAL_SPF | |
411 | feature. You must also have DKIM support, so you cannot set the | |
412 | DISABLE_DKIM feature. Once both of those conditions have been met | |
413 | you can enable DMARC in Local/Makefile: | |
414 | ||
415 | EXPERIMENTAL_DMARC=yes | |
416 | LDFLAGS += -lopendmarc | |
417 | # CFLAGS += -I/usr/local/include | |
418 | # LDFLAGS += -L/usr/local/lib | |
419 | ||
420 | The first line sets the feature to include the correct code, and | |
421 | the second line says to link the libopendmarc libraries into the | |
422 | exim binary. The commented out lines should be uncommented if you | |
423 | built opendmarc from source and installed in the default location. | |
424 | Adjust the paths if you installed them elsewhere, but you do not | |
425 | need to uncomment them if an rpm (or you) installed them in the | |
426 | package controlled locations (/usr/include and /usr/lib). | |
427 | ||
428 | ||
429 | 2. Use the following global settings to configure DMARC: | |
430 | ||
9f765fee | 431 | Optional: |
1899bab2 TL |
432 | dmarc_tld_file Defines the location of a text file of valid |
433 | top level domains the opendmarc library uses | |
434 | during domain parsing. Maintained by Mozilla, | |
435 | the most current version can be downloaded | |
436 | from a link at http://publicsuffix.org/list/. | |
9f765fee HSHR |
437 | If unset, "/etc/exim/opendmarc.tlds" (hardcoded) |
438 | is used. | |
1899bab2 TL |
439 | |
440 | Optional: | |
441 | dmarc_history_file Defines the location of a file to log results | |
442 | of dmarc verification on inbound emails. The | |
443 | contents are importable by the opendmarc tools | |
444 | which will manage the data, send out DMARC | |
445 | reports, and expire the data. Make sure the | |
446 | directory of this file is writable by the user | |
447 | exim runs as. | |
448 | ||
449 | dmarc_forensic_sender The email address to use when sending a | |
450 | forensic report detailing alignment failures | |
451 | if a sender domain's dmarc record specifies it | |
452 | and you have configured Exim to send them. | |
453 | Default: do-not-reply@$default_hostname | |
454 | ||
455 | ||
456 | 3. By default, the DMARC processing will run for any remote, | |
457 | non-authenticated user. It makes sense to only verify DMARC | |
458 | status of messages coming from remote, untrusted sources. You can | |
459 | use standard conditions such as hosts, senders, etc, to decide that | |
460 | DMARC verification should *not* be performed for them and disable | |
461 | DMARC with a control setting: | |
462 | ||
12d0043d | 463 | control = dmarc_disable_verify |
1899bab2 TL |
464 | |
465 | A DMARC record can also specify a "forensic address", which gives | |
466 | exim an email address to submit reports about failed alignment. | |
467 | Exim does not do this by default because in certain conditions it | |
468 | results in unintended information leakage (what lists a user might | |
469 | be subscribed to, etc). You must configure exim to submit forensic | |
470 | reports to the owner of the domain. If the DMARC record contains a | |
471 | forensic address and you specify the control statement below, then | |
472 | exim will send these forensic emails. It's also advised that you | |
473 | configure a dmarc_forensic_sender because the default sender address | |
474 | construction might be inadequate. | |
475 | ||
7b2f71c1 | 476 | control = dmarc_enable_forensic |
1899bab2 TL |
477 | |
478 | (AGAIN: You can choose not to send these forensic reports by simply | |
7b2f71c1 | 479 | not putting the dmarc_enable_forensic control line at any point in |
1899bab2 TL |
480 | your exim config. If you don't tell it to send them, it will not |
481 | send them.) | |
482 | ||
483 | There are no options to either control. Both must appear before | |
484 | the DATA acl. | |
485 | ||
486 | ||
487 | 4. You can now run DMARC checks in incoming SMTP by using the | |
488 | "dmarc_status" ACL condition in the DATA ACL. You are required to | |
489 | call the spf condition first in the ACLs, then the "dmarc_status" | |
490 | condition. Putting this condition in the ACLs is required in order | |
491 | for a DMARC check to actually occur. All of the variables are set | |
492 | up before the DATA ACL, but there is no actual DMARC check that | |
493 | occurs until a "dmarc_status" condition is encountered in the ACLs. | |
494 | ||
495 | The dmarc_status condition takes a list of strings on its | |
496 | right-hand side. These strings describe recommended action based | |
497 | on the DMARC check. To understand what the policy recommendations | |
498 | mean, refer to the DMARC website above. Valid strings are: | |
499 | ||
500 | o accept The DMARC check passed and the library recommends | |
501 | accepting the email. | |
502 | o reject The DMARC check failed and the library recommends | |
503 | rejecting the email. | |
504 | o quarantine The DMARC check failed and the library recommends | |
505 | keeping it for further inspection. | |
7a8678e6 | 506 | o none The DMARC check passed and the library recommends |
507 | no specific action, neutral. | |
1899bab2 TL |
508 | o norecord No policy section in the DMARC record for this |
509 | sender domain. | |
510 | o nofrom Unable to determine the domain of the sender. | |
7a8678e6 | 511 | o temperror Library error or dns error. |
05070e30 | 512 | o off The DMARC check was disabled for this email. |
1899bab2 TL |
513 | |
514 | You can prefix each string with an exclamation mark to invert its | |
515 | meaning, for example "!accept" will match all results but | |
516 | "accept". The string list is evaluated left-to-right in a | |
517 | short-circuit fashion. When a string matches the outcome of the | |
518 | DMARC check, the condition succeeds. If none of the listed | |
519 | strings matches the outcome of the DMARC check, the condition | |
520 | fails. | |
521 | ||
522 | Of course, you can also use any other lookup method that Exim | |
523 | supports, including LDAP, Postgres, MySQL, etc, as long as the | |
8c8b8274 | 524 | result is a list of colon-separated strings. |
1899bab2 TL |
525 | |
526 | Several expansion variables are set before the DATA ACL is | |
527 | processed, and you can use them in this ACL. The following | |
528 | expansion variables are available: | |
529 | ||
530 | o $dmarc_status | |
531 | This is a one word status indicating what the DMARC library | |
8c8b8274 TL |
532 | thinks of the email. It is a combination of the results of |
533 | DMARC record lookup and the SPF/DKIM/DMARC processing results | |
534 | (if a DMARC record was found). The actual policy declared | |
535 | in the DMARC record is in a separate expansion variable. | |
1899bab2 TL |
536 | |
537 | o $dmarc_status_text | |
538 | This is a slightly longer, human readable status. | |
539 | ||
540 | o $dmarc_used_domain | |
541 | This is the domain which DMARC used to look up the DMARC | |
542 | policy record. | |
543 | ||
8c8b8274 TL |
544 | o $dmarc_domain_policy |
545 | This is the policy declared in the DMARC record. Valid values | |
546 | are "none", "reject" and "quarantine". It is blank when there | |
547 | is any error, including no DMARC record. | |
548 | ||
1899bab2 TL |
549 | o $dmarc_ar_header |
550 | This is the entire Authentication-Results header which you can | |
551 | add using an add_header modifier. | |
552 | ||
553 | ||
554 | 5. How to enable DMARC advanced operation: | |
555 | By default, Exim's DMARC configuration is intended to be | |
556 | non-intrusive and conservative. To facilitate this, Exim will not | |
557 | create any type of logging files without explicit configuration by | |
558 | you, the admin. Nor will Exim send out any emails/reports about | |
559 | DMARC issues without explicit configuration by you, the admin (other | |
560 | than typical bounce messages that may come about due to ACL | |
561 | processing or failure delivery issues). | |
562 | ||
563 | In order to log statistics suitable to be imported by the opendmarc | |
564 | tools, you need to: | |
565 | a. Configure the global setting dmarc_history_file. | |
566 | b. Configure cron jobs to call the appropriate opendmarc history | |
567 | import scripts and truncating the dmarc_history_file. | |
568 | ||
569 | In order to send forensic reports, you need to: | |
570 | a. Configure the global setting dmarc_forensic_sender. | |
571 | b. Configure, somewhere before the DATA ACL, the control option to | |
572 | enable sending DMARC forensic reports. | |
573 | ||
574 | ||
575 | 6. Example usage: | |
576 | (RCPT ACL) | |
577 | warn domains = +local_domains | |
578 | hosts = +local_hosts | |
12d0043d | 579 | control = dmarc_disable_verify |
1899bab2 TL |
580 | |
581 | warn !domains = +screwed_up_dmarc_records | |
582 | control = dmarc_enable_forensic | |
583 | ||
8c8b8274 TL |
584 | warn condition = (lookup if destined to mailing list) |
585 | set acl_m_mailing_list = 1 | |
586 | ||
1899bab2 TL |
587 | (DATA ACL) |
588 | warn dmarc_status = accept : none : off | |
589 | !authenticated = * | |
590 | log_message = DMARC DEBUG: $dmarc_status $dmarc_used_domain | |
591 | add_header = $dmarc_ar_header | |
592 | ||
593 | warn dmarc_status = !accept | |
594 | !authenticated = * | |
595 | log_message = DMARC DEBUG: '$dmarc_status' for $dmarc_used_domain | |
596 | ||
597 | warn dmarc_status = quarantine | |
598 | !authenticated = * | |
599 | set $acl_m_quarantine = 1 | |
600 | # Do something in a transport with this flag variable | |
601 | ||
8c8b8274 TL |
602 | deny condition = ${if eq{$dmarc_domain_policy}{reject}} |
603 | condition = ${if eq{$acl_m_mailing_list}{1}} | |
604 | message = Messages from $dmarc_used_domain break mailing lists | |
605 | ||
1899bab2 TL |
606 | deny dmarc_status = reject |
607 | !authenticated = * | |
7b2f71c1 | 608 | message = Message from $dmarc_used_domain failed sender's DMARC policy, REJECT |
1899bab2 TL |
609 | |
610 | ||
611 | ||
043b1248 JH |
612 | DANE |
613 | ------------------------------------------------------------ | |
7cac846b JH |
614 | DNS-based Authentication of Named Entities, as applied |
615 | to SMTP over TLS, provides assurance to a client that | |
616 | it is actually talking to the server it wants to rather | |
617 | than some attacker operating a Man In The Middle (MITM) | |
618 | operation. The latter can terminate the TLS connection | |
619 | you make, and make another one to the server (so both | |
620 | you and the server still think you have an encrypted | |
621 | connection) and, if one of the "well known" set of | |
622 | Certificate Authorities has been suborned - something | |
623 | which *has* been seen already (2014), a verifiable | |
624 | certificate (if you're using normal root CAs, eg. the | |
625 | Mozilla set, as your trust anchors). | |
626 | ||
627 | What DANE does is replace the CAs with the DNS as the | |
628 | trust anchor. The assurance is limited to a) the possibility | |
629 | that the DNS has been suborned, b) mistakes made by the | |
630 | admins of the target server. The attack surface presented | |
631 | by (a) is thought to be smaller than that of the set | |
632 | of root CAs. | |
633 | ||
0e66b3b6 JH |
634 | It also allows the server to declare (implicitly) that |
635 | connections to it should use TLS. An MITM could simply | |
636 | fail to pass on a server's STARTTLS. | |
637 | ||
7cac846b JH |
638 | DANE scales better than having to maintain (and |
639 | side-channel communicate) copies of server certificates | |
640 | for every possible target server. It also scales | |
641 | (slightly) better than having to maintain on an SMTP | |
642 | client a copy of the standard CAs bundle. It also | |
643 | means not having to pay a CA for certificates. | |
644 | ||
645 | DANE requires a server operator to do three things: | |
646 | 1) run DNSSEC. This provides assurance to clients | |
647 | that DNS lookups they do for the server have not | |
401a8935 JH |
648 | been tampered with. The domain MX record applying |
649 | to this server, its A record, its TLSA record and | |
650 | any associated CNAME records must all be covered by | |
651 | DNSSEC. | |
7cac846b JH |
652 | 2) add TLSA DNS records. These say what the server |
653 | certificate for a TLS connection should be. | |
654 | 3) offer a server certificate, or certificate chain, | |
655 | in TLS connections which is traceable to the one | |
656 | defined by (one of?) the TSLA records | |
657 | ||
658 | There are no changes to Exim specific to server-side | |
659 | operation of DANE. | |
660 | ||
661 | The TLSA record for the server may have "certificate | |
0e66b3b6 | 662 | usage" of DANE-TA(2) or DANE-EE(3). The latter specifies |
7cac846b JH |
663 | the End Entity directly, i.e. the certificate involved |
664 | is that of the server (and should be the sole one transmitted | |
665 | during the TLS handshake); this is appropriate for a | |
666 | single system, using a self-signed certificate. | |
0e66b3b6 | 667 | DANE-TA usage is effectively declaring a specific CA |
7cac846b JH |
668 | to be used; this might be a private CA or a public, |
669 | well-known one. A private CA at simplest is just | |
670 | a self-signed certificate which is used to sign | |
671 | cerver certificates, but running one securely does | |
672 | require careful arrangement. If a private CA is used | |
673 | then either all clients must be primed with it, or | |
674 | (probably simpler) the server TLS handshake must transmit | |
675 | the entire certificate chain from CA to server-certificate. | |
676 | If a public CA is used then all clients must be primed with it | |
677 | (losing one advantage of DANE) - but the attack surface is | |
678 | reduced from all public CAs to that single CA. | |
0e66b3b6 | 679 | DANE-TA is commonly used for several services and/or |
7cac846b JH |
680 | servers, each having a TLSA query-domain CNAME record, |
681 | all of which point to a single TLSA record. | |
682 | ||
683 | The TLSA record should have a Selector field of SPKI(1) | |
401a8935 JH |
684 | and a Matching Type field of SHA2-512(2). |
685 | ||
686 | At the time of writing, https://www.huque.com/bin/gen_tlsa | |
687 | is useful for quickly generating TLSA records; and commands like | |
688 | ||
689 | openssl x509 -in -pubkey -noout <certificate.pem \ | |
690 | | openssl rsa -outform der -pubin 2>/dev/null \ | |
691 | | openssl sha512 \ | |
692 | | awk '{print $2}' | |
693 | ||
694 | are workable for 4th-field hashes. | |
7cac846b | 695 | |
0e66b3b6 | 696 | For use with the DANE-TA model, server certificates |
7cac846b JH |
697 | must have a correct name (SubjectName or SubjectAltName). |
698 | ||
699 | The use of OCSP-stapling should be considered, allowing | |
700 | for fast revocation of certificates (which would otherwise | |
eeb9276b | 701 | be limited by the DNS TTL on the TLSA records). However, |
0e66b3b6 | 702 | this is likely to only be usable with DANE-TA. NOTE: the |
fca41d5a JH |
703 | default of requesting OCSP for all hosts is modified iff |
704 | DANE is in use, to: | |
705 | ||
706 | hosts_request_ocsp = ${if or { {= {0}{$tls_out_tlsa_usage}} \ | |
707 | {= {4}{$tls_out_tlsa_usage}} } \ | |
594706ea | 708 | {*}{}} |
fca41d5a JH |
709 | |
710 | The (new) variable $tls_out_tlsa_usage is a bitfield with | |
711 | numbered bits set for TLSA record usage codes. | |
712 | The zero above means DANE was not in use, | |
0e66b3b6 JH |
713 | the four means that only DANE-TA usage TLSA records were |
714 | found. If the definition of hosts_request_ocsp includes the | |
715 | string "tls_out_tlsa_usage", they are re-expanded in time to | |
716 | control the OCSP request. | |
594706ea | 717 | |
fca41d5a | 718 | This modification of hosts_request_ocsp is only done if |
036ed0db JH |
719 | it has the default value of "*". Admins who change it, and |
720 | those who use hosts_require_ocsp, should consider the interaction | |
721 | with DANE in their OCSP settings. | |
7cac846b JH |
722 | |
723 | ||
7a31d643 | 724 | For client-side DANE there are two new smtp transport options, |
4b0fe319 | 725 | hosts_try_dane and hosts_require_dane. |
7a31d643 | 726 | [ should they be domain-based rather than host-based? ] |
7cac846b | 727 | |
4b0fe319 JH |
728 | Hosts_require_dane will result in failure if the target host |
729 | is not DNSSEC-secured. | |
730 | ||
7cac846b JH |
731 | DANE will only be usable if the target host has DNSSEC-secured |
732 | MX, A and TLSA records. | |
733 | ||
0e66b3b6 | 734 | A TLSA lookup will be done if either of the above options match |
4c04137d | 735 | and the host-lookup succeeded using dnssec. |
3750d68d | 736 | If a TLSA lookup is done and succeeds, a DANE-verified TLS connection |
4b0fe319 JH |
737 | will be required for the host. If it does not, the host will not |
738 | be used; there is no fallback to non-DANE or non-TLS. | |
7cac846b | 739 | |
3750d68d JH |
740 | If DANE is requested and useable (see above) the following transport |
741 | options are ignored: | |
0e66b3b6 | 742 | hosts_require_tls |
043b1248 JH |
743 | tls_verify_hosts |
744 | tls_try_verify_hosts | |
745 | tls_verify_certificates | |
746 | tls_crl | |
747 | tls_verify_cert_hostnames | |
043b1248 | 748 | |
3750d68d JH |
749 | If DANE is not usable, whether requested or not, and CA-anchored |
750 | verification evaluation is wanted, the above variables should be set | |
751 | appropriately. | |
752 | ||
7cac846b JH |
753 | Currently dnssec_request_domains must be active (need to think about that) |
754 | and dnssec_require_domains is ignored. | |
043b1248 | 755 | |
eeb9276b JH |
756 | If verification was successful using DANE then the "CV" item |
757 | in the delivery log line will show as "CV=dane". | |
758 | ||
594706ea JH |
759 | There is a new variable $tls_out_dane which will have "yes" if |
760 | verification succeeded using DANE and "no" otherwise (only useful | |
8d692470 | 761 | in combination with EXPERIMENTAL_EVENT), and a new variable |
594706ea JH |
762 | $tls_out_tlsa_usage (detailed above). |
763 | ||
899b8bbc JH |
764 | Under GnuTLS, DANE is only supported from versin 3.0.0 onwards |
765 | ||
e51c7be2 | 766 | |
c65be124 | 767 | |
895fbaf2 JH |
768 | DSN extra information |
769 | --------------------- | |
770 | If compiled with EXPERIMENTAL_DSN_INFO extra information will be added | |
771 | to DSN fail messages ("bounces"), when available. The intent is to aid | |
772 | tracing of specific failing messages, when presented with a "bounce" | |
773 | complaint and needing to search logs. | |
774 | ||
775 | ||
776 | The remote MTA IP address, with port number if nonstandard. | |
777 | Example: | |
778 | Remote-MTA: X-ip; [127.0.0.1]:587 | |
779 | Rationale: | |
780 | Several addresses may correspond to the (already available) | |
781 | dns name for the remote MTA. | |
782 | ||
783 | The remote MTA connect-time greeting. | |
784 | Example: | |
785 | X-Remote-MTA-smtp-greeting: X-str; 220 the.local.host.name ESMTP Exim x.yz Tue, 2 Mar 1999 09:44:33 +0000 | |
786 | Rationale: | |
787 | This string sometimes presents the remote MTA's idea of its | |
788 | own name, and sometimes identifies the MTA software. | |
789 | ||
790 | The remote MTA response to HELO or EHLO. | |
791 | Example: | |
792 | X-Remote-MTA-helo-response: X-str; 250-the.local.host.name Hello localhost [127.0.0.1] | |
793 | Limitations: | |
794 | Only the first line of a multiline response is recorded. | |
795 | Rationale: | |
796 | This string sometimes presents the remote MTA's view of | |
797 | the peer IP connecting to it. | |
798 | ||
799 | The reporting MTA detailed diagnostic. | |
800 | Example: | |
801 | X-Exim-Diagnostic: X-str; SMTP error from remote mail server after RCPT TO:<d3@myhost.test.ex>: 550 hard error | |
802 | Rationale: | |
4c04137d | 803 | This string sometimes give extra information over the |
895fbaf2 JH |
804 | existing (already available) Diagnostic-Code field. |
805 | ||
806 | ||
807 | Note that non-RFC-documented field names and data types are used. | |
808 | ||
809 | ||
5bde3efa ACK |
810 | LMDB Lookup support |
811 | ------------------- | |
812 | LMDB is an ultra-fast, ultra-compact, crash-proof key-value embedded data store. | |
4c04137d | 813 | It is modeled loosely on the BerkeleyDB API. You should read about the feature |
5bde3efa ACK |
814 | set as well as operation modes at https://symas.com/products/lightning-memory-mapped-database/ |
815 | ||
816 | LMDB single key lookup support is provided by linking to the LMDB C library. | |
817 | The current implementation does not support writing to the LMDB database. | |
818 | ||
819 | Visit https://github.com/LMDB/lmdb to download the library or find it in your | |
820 | operating systems package repository. | |
821 | ||
822 | If building from source, this description assumes that headers will be in | |
823 | /usr/local/include, and that the libraries are in /usr/local/lib. | |
824 | ||
825 | 1. In order to build exim with LMDB lookup support add or uncomment | |
826 | ||
827 | EXPERIMENTAL_LMDB=yes | |
828 | ||
829 | to your Local/Makefile. (Re-)build/install exim. exim -d should show | |
830 | Experimental_LMDB in the line "Support for:". | |
831 | ||
832 | EXPERIMENTAL_LMDB=yes | |
833 | LDFLAGS += -llmdb | |
834 | # CFLAGS += -I/usr/local/include | |
835 | # LDFLAGS += -L/usr/local/lib | |
836 | ||
837 | The first line sets the feature to include the correct code, and | |
838 | the second line says to link the LMDB libraries into the | |
839 | exim binary. The commented out lines should be uncommented if you | |
840 | built LMDB from source and installed in the default location. | |
841 | Adjust the paths if you installed them elsewhere, but you do not | |
842 | need to uncomment them if an rpm (or you) installed them in the | |
843 | package controlled locations (/usr/include and /usr/lib). | |
844 | ||
845 | 2. Create your LMDB files, you can use the mdb_load utility which is | |
846 | part of the LMDB distribution our your favourite language bindings. | |
847 | ||
848 | 3. Add the single key lookups to your exim.conf file, example lookups | |
849 | are below. | |
850 | ||
851 | ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}} | |
852 | ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}fail} | |
853 | ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}} | |
895fbaf2 | 854 | |
ed0512a1 | 855 | |
3369a853 ACK |
856 | Queuefile transport |
857 | ------------------- | |
858 | Queuefile is a pseudo transport which does not perform final delivery. | |
859 | It simply copies the exim spool files out of the spool directory into | |
860 | an external directory retaining the exim spool format. | |
861 | ||
862 | The spool files can then be processed by external processes and then | |
863 | requeued into exim spool directories for final delivery. | |
864 | ||
865 | The motivation/inspiration for the transport is to allow external | |
866 | processes to access email queued by exim and have access to all the | |
867 | information which would not be available if the messages were delivered | |
868 | to the process in the standard email formats. | |
869 | ||
870 | The mailscanner package is one of the processes that can take advantage | |
871 | of this transport to filter email. | |
872 | ||
873 | The transport can be used in the same way as the other existing transports, | |
874 | i.e by configuring a router to route mail to a transport configured with | |
875 | the queuefile driver. | |
876 | ||
877 | The transport only takes one option: | |
878 | ||
879 | * directory - This is used to specify the directory messages should be | |
880 | copied to | |
881 | ||
882 | The generic transport options (body_only, current_directory, disable_logging, | |
883 | debug_print, delivery_date_add, envelope_to_add, event_action, group, | |
884 | headers_add, headers_only, headers_remove, headers_rewrite, home_directory, | |
885 | initgroups, max_parallel, message_size_limit, rcpt_include_affixes, | |
886 | retry_use_local_part, return_path, return_path_add, shadow_condition, | |
887 | shadow_transport, transport_filter, transport_filter_timeout, user) are | |
888 | ignored. | |
889 | ||
890 | Sample configuration: | |
891 | ||
892 | (Router) | |
893 | ||
894 | scan: | |
895 | driver = accept | |
896 | transport = scan | |
897 | ||
898 | (Transport) | |
899 | ||
900 | scan: | |
901 | driver = queuefile | |
902 | directory = /var/spool/baruwa-scanner/input | |
903 | ||
904 | ||
905 | In order to build exim with Queuefile transport support add or uncomment | |
906 | ||
907 | EXPERIMENTAL_QUEUEFILE=yes | |
908 | ||
909 | to your Local/Makefile. (Re-)build/install exim. exim -d should show | |
910 | Experimental_QUEUEFILE in the line "Support for:". | |
911 | ||
912 | ||
ee161e8f PH |
913 | -------------------------------------------------------------- |
914 | End of file | |
915 | -------------------------------------------------------------- |