Commit | Line | Data |
---|---|---|
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 | ||
002fcd22 JH |
315 | The following main-section options become available: |
316 | srs_config string | |
317 | srs_hashlength int | |
318 | srs_hashmin int | |
319 | srs_maxage int | |
320 | srs_secrets string | |
321 | srs_usehash bool | |
322 | srs_usetimestamp bool | |
323 | ||
324 | The redirect router gains these options (all of type string, unset by default): | |
325 | srs | |
326 | srs_alias | |
327 | srs_condition | |
328 | srs_dbinsert | |
329 | srs_dbselect | |
330 | ||
331 | The following variables become available: | |
332 | $srs_db_address | |
333 | $srs_db_key | |
334 | $srs_orig_recipient | |
335 | $srs_orig_sender | |
336 | $srs_recipient | |
337 | $srs_status | |
338 | ||
339 | The predefined feature-macro _HAVE_SRS will be present. | |
340 | Additional delivery log line elements, tagged with "SRS=" will show the srs sender. | |
341 | For configuration information see https://github.com/Exim/exim/wiki/SRS . | |
342 | ||
343 | ||
ee161e8f | 344 | |
f413521a | 345 | |
0e1ccf44 PP |
346 | DCC Support |
347 | -------------------------------------------------------------- | |
d36254f2 | 348 | Distributed Checksum Clearinghouse; http://www.rhyolite.com/dcc/ |
0e1ccf44 PP |
349 | |
350 | *) Building exim | |
351 | ||
352 | In order to build exim with DCC support add | |
353 | ||
354 | EXPERIMENTAL_DCC=yes | |
355 | ||
356 | to your Makefile. (Re-)build/install exim. exim -d should show | |
357 | EXPERIMENTAL_DCC under "Support for". | |
358 | ||
359 | ||
360 | *) Configuration | |
361 | ||
362 | In the main section of exim.cf add at least | |
363 | dccifd_address = /usr/local/dcc/var/dccifd | |
364 | or | |
365 | dccifd_address = <ip> <port> | |
366 | ||
367 | In the DATA ACL you can use the new condition | |
368 | dcc = * | |
369 | ||
370 | After that "$dcc_header" contains the X-DCC-Header. | |
371 | ||
d36a0501 | 372 | Return values are: |
0e1ccf44 PP |
373 | fail for overall "R", "G" from dccifd |
374 | defer for overall "T" from dccifd | |
375 | accept for overall "A", "S" from dccifd | |
376 | ||
377 | dcc = */defer_ok works as for spamd. | |
378 | ||
379 | The "$dcc_result" variable contains the overall result from DCC | |
380 | answer. There will an X-DCC: header added to the mail. | |
381 | ||
382 | Usually you'll use | |
383 | defer !dcc = * | |
384 | to greylist with DCC. | |
385 | ||
386 | If you set, in the main section, | |
387 | dcc_direct_add_header = true | |
388 | then the dcc header will be added "in deep" and if the spool | |
389 | file was already written it gets removed. This forces Exim to | |
390 | write it again if needed. This helps to get the DCC Header | |
391 | through to eg. SpamAssassin. | |
392 | ||
393 | If you want to pass even more headers in the middle of the | |
394 | DATA stage you can set | |
395 | $acl_m_dcc_add_header | |
05c39afa | 396 | to tell the DCC routines to add more information; eg, you might set |
0e1ccf44 PP |
397 | this to some results from ClamAV. Be careful. Header syntax is |
398 | not checked and is added "as is". | |
399 | ||
05c39afa JH |
400 | In case you've troubles with sites sending the same queue items from several |
401 | hosts and fail to get through greylisting you can use | |
402 | $acl_m_dcc_override_client_ip | |
403 | ||
404 | Setting $acl_m_dcc_override_client_ip to an IP address overrides the default | |
405 | of $sender_host_address. eg. use the following ACL in DATA stage: | |
406 | ||
407 | warn set acl_m_dcc_override_client_ip = \ | |
408 | ${lookup{$sender_helo_name}nwildlsearch{/etc/mail/multipleip_sites}{$value}{}} | |
409 | condition = ${if def:acl_m_dcc_override_client_ip} | |
410 | log_message = dbg: acl_m_dcc_override_client_ip set to \ | |
411 | $acl_m_dcc_override_client_ip | |
412 | ||
413 | Then set something like | |
414 | # cat /etc/mail/multipleip_sites | |
415 | mout-xforward.gmx.net 82.165.159.12 | |
416 | mout.gmx.net 212.227.15.16 | |
417 | ||
4c04137d | 418 | Use a reasonable IP. eg. one the sending cluster actually uses. |
0e1ccf44 | 419 | |
48155ab3 JH |
420 | |
421 | ||
895fbaf2 JH |
422 | DSN extra information |
423 | --------------------- | |
424 | If compiled with EXPERIMENTAL_DSN_INFO extra information will be added | |
425 | to DSN fail messages ("bounces"), when available. The intent is to aid | |
426 | tracing of specific failing messages, when presented with a "bounce" | |
427 | complaint and needing to search logs. | |
428 | ||
429 | ||
430 | The remote MTA IP address, with port number if nonstandard. | |
431 | Example: | |
432 | Remote-MTA: X-ip; [127.0.0.1]:587 | |
433 | Rationale: | |
434 | Several addresses may correspond to the (already available) | |
435 | dns name for the remote MTA. | |
436 | ||
437 | The remote MTA connect-time greeting. | |
438 | Example: | |
439 | X-Remote-MTA-smtp-greeting: X-str; 220 the.local.host.name ESMTP Exim x.yz Tue, 2 Mar 1999 09:44:33 +0000 | |
440 | Rationale: | |
441 | This string sometimes presents the remote MTA's idea of its | |
442 | own name, and sometimes identifies the MTA software. | |
443 | ||
444 | The remote MTA response to HELO or EHLO. | |
445 | Example: | |
446 | X-Remote-MTA-helo-response: X-str; 250-the.local.host.name Hello localhost [127.0.0.1] | |
447 | Limitations: | |
448 | Only the first line of a multiline response is recorded. | |
449 | Rationale: | |
450 | This string sometimes presents the remote MTA's view of | |
451 | the peer IP connecting to it. | |
452 | ||
453 | The reporting MTA detailed diagnostic. | |
454 | Example: | |
455 | X-Exim-Diagnostic: X-str; SMTP error from remote mail server after RCPT TO:<d3@myhost.test.ex>: 550 hard error | |
456 | Rationale: | |
4c04137d | 457 | This string sometimes give extra information over the |
895fbaf2 JH |
458 | existing (already available) Diagnostic-Code field. |
459 | ||
460 | ||
461 | Note that non-RFC-documented field names and data types are used. | |
462 | ||
463 | ||
5bde3efa ACK |
464 | LMDB Lookup support |
465 | ------------------- | |
466 | LMDB is an ultra-fast, ultra-compact, crash-proof key-value embedded data store. | |
4c04137d | 467 | It is modeled loosely on the BerkeleyDB API. You should read about the feature |
5bde3efa ACK |
468 | set as well as operation modes at https://symas.com/products/lightning-memory-mapped-database/ |
469 | ||
470 | LMDB single key lookup support is provided by linking to the LMDB C library. | |
471 | The current implementation does not support writing to the LMDB database. | |
472 | ||
473 | Visit https://github.com/LMDB/lmdb to download the library or find it in your | |
474 | operating systems package repository. | |
475 | ||
476 | If building from source, this description assumes that headers will be in | |
477 | /usr/local/include, and that the libraries are in /usr/local/lib. | |
478 | ||
479 | 1. In order to build exim with LMDB lookup support add or uncomment | |
480 | ||
481 | EXPERIMENTAL_LMDB=yes | |
482 | ||
483 | to your Local/Makefile. (Re-)build/install exim. exim -d should show | |
484 | Experimental_LMDB in the line "Support for:". | |
485 | ||
486 | EXPERIMENTAL_LMDB=yes | |
487 | LDFLAGS += -llmdb | |
488 | # CFLAGS += -I/usr/local/include | |
489 | # LDFLAGS += -L/usr/local/lib | |
490 | ||
491 | The first line sets the feature to include the correct code, and | |
492 | the second line says to link the LMDB libraries into the | |
493 | exim binary. The commented out lines should be uncommented if you | |
494 | built LMDB from source and installed in the default location. | |
495 | Adjust the paths if you installed them elsewhere, but you do not | |
496 | need to uncomment them if an rpm (or you) installed them in the | |
497 | package controlled locations (/usr/include and /usr/lib). | |
498 | ||
499 | 2. Create your LMDB files, you can use the mdb_load utility which is | |
500 | part of the LMDB distribution our your favourite language bindings. | |
501 | ||
502 | 3. Add the single key lookups to your exim.conf file, example lookups | |
503 | are below. | |
504 | ||
505 | ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}} | |
506 | ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}fail} | |
507 | ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}} | |
895fbaf2 | 508 | |
ed0512a1 | 509 | |
3369a853 ACK |
510 | Queuefile transport |
511 | ------------------- | |
512 | Queuefile is a pseudo transport which does not perform final delivery. | |
513 | It simply copies the exim spool files out of the spool directory into | |
514 | an external directory retaining the exim spool format. | |
515 | ||
516 | The spool files can then be processed by external processes and then | |
517 | requeued into exim spool directories for final delivery. | |
20751c76 JH |
518 | However, note carefully the warnings in the main documentation on |
519 | qpool file formats. | |
3369a853 ACK |
520 | |
521 | The motivation/inspiration for the transport is to allow external | |
522 | processes to access email queued by exim and have access to all the | |
523 | information which would not be available if the messages were delivered | |
524 | to the process in the standard email formats. | |
525 | ||
526 | The mailscanner package is one of the processes that can take advantage | |
527 | of this transport to filter email. | |
528 | ||
529 | The transport can be used in the same way as the other existing transports, | |
530 | i.e by configuring a router to route mail to a transport configured with | |
531 | the queuefile driver. | |
532 | ||
533 | The transport only takes one option: | |
534 | ||
535 | * directory - This is used to specify the directory messages should be | |
9604413b | 536 | copied to. Expanded. |
3369a853 ACK |
537 | |
538 | The generic transport options (body_only, current_directory, disable_logging, | |
539 | debug_print, delivery_date_add, envelope_to_add, event_action, group, | |
540 | headers_add, headers_only, headers_remove, headers_rewrite, home_directory, | |
541 | initgroups, max_parallel, message_size_limit, rcpt_include_affixes, | |
542 | retry_use_local_part, return_path, return_path_add, shadow_condition, | |
543 | shadow_transport, transport_filter, transport_filter_timeout, user) are | |
544 | ignored. | |
545 | ||
546 | Sample configuration: | |
547 | ||
548 | (Router) | |
549 | ||
550 | scan: | |
551 | driver = accept | |
552 | transport = scan | |
553 | ||
554 | (Transport) | |
555 | ||
556 | scan: | |
557 | driver = queuefile | |
558 | directory = /var/spool/baruwa-scanner/input | |
559 | ||
560 | ||
561 | In order to build exim with Queuefile transport support add or uncomment | |
562 | ||
563 | EXPERIMENTAL_QUEUEFILE=yes | |
564 | ||
565 | to your Local/Makefile. (Re-)build/install exim. exim -d should show | |
566 | Experimental_QUEUEFILE in the line "Support for:". | |
567 | ||
568 | ||
617d3932 JH |
569 | ARC support |
570 | ----------- | |
571 | Specification: https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-11 | |
572 | Note that this is not an RFC yet, so may change. | |
573 | ||
dc2d885a JH |
574 | [RFC 8617 was published 2019/06. Draft 11 was 2018/01. A review of the |
575 | changes has not yet been done] | |
576 | ||
617d3932 JH |
577 | ARC is intended to support the utility of SPF and DKIM in the presence of |
578 | intermediaries in the transmission path - forwarders and mailinglists - | |
579 | by establishing a cryptographically-signed chain in headers. | |
580 | ||
581 | Normally one would only bother doing ARC-signing when functioning as | |
582 | an intermediary. One might do verify for local destinations. | |
583 | ||
584 | ARC uses the notion of a "ADministrative Management Domain" (ADMD). | |
dc2d885a JH |
585 | Described in RFC 5598 (section 2.3), this is essentially a set of |
586 | mail-handling systems that mail transits that are all under the control | |
587 | of one organisation. A label should be chosen to identify the ADMD. | |
588 | Messages should be ARC-verified on entry to the ADMD, and ARC-signed on exit | |
589 | from it. | |
617d3932 JH |
590 | |
591 | ||
2b2cfa83 JH |
592 | Building with ARC Support |
593 | -- | |
594 | Enable using EXPERIMENTAL_ARC=yes in your Local/Makefile. | |
595 | You must also have DKIM present (not disabled), and you very likely | |
596 | want to have SPF enabled. | |
597 | ||
598 | ||
617d3932 JH |
599 | Verification |
600 | -- | |
601 | An ACL condition is provided to perform the "verifier actions" detailed | |
602 | in section 6 of the above specification. It may be called from the DATA ACL | |
603 | and succeeds if the result matches any of a given list. | |
604 | It also records the highest ARC instance number (the chain size) | |
605 | and verification result for later use in creating an Authentication-Results: | |
606 | standard header. | |
607 | ||
608 | verify = arc/<acceptable_list> none:fail:pass | |
609 | ||
610 | add_header = :at_start:${authresults {<admd-identifier>}} | |
611 | ||
612 | Note that it would be wise to strip incoming messages of A-R headers | |
613 | that claim to be from our own <admd-identifier>. | |
614 | ||
a1d4300b | 615 | There are four new variables: |
9cffa436 JH |
616 | |
617 | $arc_state One of pass, fail, none | |
618 | $arc_state_reason (if fail, why) | |
08bd2689 JH |
619 | $arc_domains colon-sep list of ARC chain domains, in chain order. |
620 | problematic elements may have empty list elements | |
ea7b1f16 | 621 | $arc_oldest_pass lowest passing instance number of chain |
93c931f8 | 622 | |
bce15b62 JH |
623 | Example: |
624 | logwrite = oldest-p-ams: <${reduce {$lh_ARC-Authentication-Results:} \ | |
625 | {} \ | |
626 | {${if = {$arc_oldest_pass} \ | |
627 | {${extract {i}{${extract {1}{;}{$item}}}}} \ | |
628 | {$item} {$value}}} \ | |
629 | }> | |
630 | ||
617d3932 JH |
631 | Receive log lines for an ARC pass will be tagged "ARC". |
632 | ||
633 | ||
634 | Signing | |
635 | -- | |
a93dbf44 | 636 | arc_sign = <admd-identifier> : <selector> : <privkey> [ : <options> ] |
617d3932 JH |
637 | An option on the smtp transport, which constructs and prepends to the message |
638 | an ARC set of headers. The textually-first Authentication-Results: header | |
639 | is used as a basis (you must have added one on entry to the ADMD). | |
9f7d9fa1 | 640 | Expanded as a whole; if unset, empty or forced-failure then no signing is done. |
5054c4fd | 641 | If it is set, all of the first three elements must be non-empty. |
617d3932 | 642 | |
a93dbf44 | 643 | The fourth element is optional, and if present consists of a comma-separated list |
0e83c148 JH |
644 | of options. The options implemented are |
645 | ||
646 | timestamps Add a t= tag to the generated AMS and AS headers, with the | |
647 | current time. | |
648 | expire[=<val>] Add an x= tag to the generated AMS header, with an expiry time. | |
649 | If the value <val> is an plain number it is used unchanged. | |
650 | If it starts with a '+' then the following number is added | |
651 | to the current time, as an offset in seconds. | |
652 | If a value is not given it defaults to a one month offset. | |
a93dbf44 JH |
653 | |
654 | [As of writing, gmail insist that a t= tag on the AS is mandatory] | |
655 | ||
afcdd656 PP |
656 | Caveats: |
657 | * There must be an Authentication-Results header, presumably added by an ACL | |
658 | while receiving the message, for the same ADMD, for arc_sign to succeed. | |
659 | This requires careful coordination between inbound and outbound logic. | |
5054c4fd JH |
660 | |
661 | Only one A-R header is taken account of. This is a limitation versus | |
662 | the ARC spec (which says that all A-R headers from within the ADMD must | |
663 | be used). | |
664 | ||
afcdd656 PP |
665 | * If passing a message to another system, such as a mailing-list manager |
666 | (MLM), between receipt and sending, be wary of manipulations to headers made | |
667 | by the MLM. | |
668 | + For instance, Mailman with REMOVE_DKIM_HEADERS==3 might improve | |
669 | deliverability in a pre-ARC world, but that option also renames the | |
670 | Authentication-Results header, which breaks signing. | |
5054c4fd | 671 | |
afcdd656 PP |
672 | * Even if you use multiple DKIM keys for different domains, the ARC concept |
673 | should try to stick to one ADMD, so pick a primary domain and use that for | |
674 | AR headers and outbound signing. | |
675 | ||
5add7dc4 JH |
676 | Signing is not compatible with cutthrough delivery; any (before expansion) |
677 | value set for the option will result in cutthrough delivery not being | |
678 | used via the transport in question. | |
679 | ||
617d3932 JH |
680 | |
681 | ||
8ac90765 | 682 | |
b10c87b3 JH |
683 | TLS Session Resumption |
684 | ---------------------- | |
43e2db44 | 685 | TLS Session Resumption for TLS 1.2 and TLS 1.3 connections can be used (defined |
b10c87b3 | 686 | in RFC 5077 for 1.2). The support for this can be included by building with |
43e2db44 JH |
687 | EXPERIMENTAL_TLS_RESUME defined. This requires GnuTLS 3.6.3 or OpenSSL 1.1.1 |
688 | (or later). | |
b10c87b3 JH |
689 | |
690 | Session resumption (this is the "stateless" variant) involves the server sending | |
691 | a "session ticket" to the client on one connection, which can be stored by the | |
692 | client and used for a later session. The ticket contains sufficient state for | |
693 | the server to reconstruct the TLS session, avoiding some expensive crypto | |
694 | calculation and one full packet roundtrip time. | |
695 | ||
696 | Operational cost/benefit: | |
697 | The extra data being transmitted costs a minor amount, and the client has | |
68c62739 | 698 | extra costs in storing and retrieving the data. |
b10c87b3 | 699 | |
68c62739 JH |
700 | In the Exim/Gnutls implementation the extra cost on an initial connection |
701 | which is TLS1.2 over a loopback path is about 6ms on 2017-laptop class hardware. | |
702 | The saved cost on a subsequent connection is about 4ms; three or more | |
703 | connections become a net win. On longer network paths, two or more | |
704 | connections will have an average lower startup time thanks to the one | |
705 | saved packet roundtrip. TLS1.3 will save the crypto cpu costs but not any | |
706 | packet roundtrips. | |
707 | ||
708 | Since a new hints DB is used, the hints DB maintenance should be updated | |
709 | to additionally handle "tls". | |
b10c87b3 JH |
710 | |
711 | Security aspects: | |
712 | The session ticket is encrypted, but is obviously an additional security | |
68c62739 JH |
713 | vulnarability surface. An attacker able to decrypt it would have access |
714 | all connections using the resumed session. | |
715 | The session ticket encryption key is not committed to storage by the server | |
dea4b568 JH |
716 | and is rotated regularly (OpenSSL: 1hr, and one previous key is used for |
717 | overlap; GnuTLS 6hr but does not specify any overlap). | |
718 | Tickets have limited lifetime (2hr, and new ones issued after 1hr under | |
719 | OpenSSL. GnuTLS 2hr, appears to not do overlap). | |
b10c87b3 | 720 | |
68c62739 JH |
721 | There is a question-mark over the security of the Diffie-Helman parameters |
722 | used for session negotiation. TBD. q-value; cf bug 1895 | |
b10c87b3 JH |
723 | |
724 | Observability: | |
725 | New log_selector "tls_resumption", appends an asterisk to the tls_cipher "X=" | |
68c62739 JH |
726 | element. |
727 | ||
4a1bd6b9 | 728 | Variables $tls_{in,out}_resumption have bits 0-4 indicating respectively |
68c62739 JH |
729 | support built, client requested ticket, client offered session, |
730 | server issued ticket, resume used. A suitable decode list is provided | |
731 | in the builtin macro _RESUME_DECODE for ${listextract {}{}}. | |
732 | ||
733 | Issues: | |
734 | In a resumed session: | |
11c4a22b | 735 | $tls_{in,out}_cipher will have values different to the original (under GnuTLS) |
4f1d23a1 | 736 | $tls_{in,out}_ocsp will be "not requested" or "no response", and |
f4e62a87 | 737 | hosts_require_ocsp will fail |
b10c87b3 JH |
738 | |
739 | ||
ee161e8f PH |
740 | -------------------------------------------------------------- |
741 | End of file | |
742 | -------------------------------------------------------------- |