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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 | ||
fd98a5c6 JH |
9 | PRDR support |
10 | -------------------------------------------------------------- | |
11 | ||
12 | Per-Recipient Data Reponse is an SMTP extension proposed by Eric Hall | |
13 | in a (now-expired) IETF draft from 2007. It's not hit mainstream | |
14 | use, but has apparently been implemented in the META1 MTA. | |
15 | ||
16 | There is mention at http://mail.aegee.org/intern/sendmail.html | |
17 | of a patch to sendmail "to make it PRDR capable". | |
18 | ||
19 | ref: http://www.eric-a-hall.com/specs/draft-hall-prdr-00.txt | |
20 | ||
21 | If Exim is built with EXPERIMENTAL_PRDR there is a new config | |
22 | boolean "prdr_enable" which controls whether PRDR is advertised | |
23 | as part of an EHLO response, a new "acl_data_smtp_prdr" ACL | |
24 | (called for each recipient, after data arrives but before the | |
25 | data ACL), and a new smtp transport option "hosts_try_prdr". | |
26 | ||
27 | PRDR may be used to support per-user content filtering. Without it | |
28 | one must defer any recipient after the first that has a different | |
29 | content-filter configuration. With PRDR, the RCPT-time check | |
30 | for this can be disabled when the MAIL-time $smtp_command included | |
31 | "PRDR". Any required difference in behaviour of the main DATA-time | |
32 | ACL should however depend on the PRDR-time ACL having run, as Exim | |
33 | will avoid doing so in some situations (eg. single-recipient mails). | |
34 | ||
35 | ||
36 | ||
3f7eeb86 PP |
37 | OCSP Stapling support |
38 | -------------------------------------------------------------- | |
39 | ||
d36a0501 | 40 | X.509 PKI certificates expire and can be revoked; to handle this, the |
3f7eeb86 PP |
41 | clients need some way to determine if a particular certificate, from a |
42 | particular Certificate Authority (CA), is still valid. There are three | |
43 | main ways to do so. | |
44 | ||
45 | The simplest way is to serve up a Certificate Revocation List (CRL) with | |
46 | an ordinary web-server, regenerating the CRL before it expires. The | |
47 | downside is that clients have to periodically re-download a potentially | |
48 | huge file from every certificate authority it knows of. | |
49 | ||
50 | The way with most moving parts at query time is Online Certificate | |
51 | Status Protocol (OCSP), where the client verifies the certificate | |
52 | against an OCSP server run by the CA. This lets the CA track all | |
53 | usage of the certs. This requires running software with access to the | |
54 | private key of the CA, to sign the responses to the OCSP queries. OCSP | |
55 | is based on HTTP and can be proxied accordingly. | |
56 | ||
57 | The only widespread OCSP server implementation (known to this writer) | |
58 | comes as part of OpenSSL and aborts on an invalid request, such as | |
59 | connecting to the port and then disconnecting. This requires | |
60 | re-entering the passphrase each time some random client does this. | |
61 | ||
62 | The third way is OCSP Stapling; in this, the server using a certificate | |
63 | issued by the CA periodically requests an OCSP proof of validity from | |
64 | the OCSP server, then serves it up inline as part of the TLS | |
65 | negotiation. This approach adds no extra round trips, does not let the | |
66 | CA track users, scales well with number of certs issued by the CA and is | |
67 | resilient to temporary OCSP server failures, as long as the server | |
68 | starts retrying to fetch an OCSP proof some time before its current | |
69 | proof expires. The downside is that it requires server support. | |
70 | ||
71 | If Exim is built with EXPERIMENTAL_OCSP and it was built with OpenSSL, | |
72 | then it gains one new option: "tls_ocsp_file". | |
73 | ||
74 | The file specified therein is expected to be in DER format, and contain | |
75 | an OCSP proof. Exim will serve it as part of the TLS handshake. This | |
76 | option will be re-expanded for SNI, if the tls_certificate option | |
77 | contains $tls_sni, as per other TLS options. | |
78 | ||
79 | Exim does not at this time implement any support for fetching a new OCSP | |
80 | proof. The burden is on the administrator to handle this, outside of | |
81 | Exim. The file specified should be replaced atomically, so that the | |
82 | contents are always valid. Exim will expand the "tls_ocsp_file" option | |
83 | on each connection, so a new file will be handled transparently on the | |
84 | next connection. | |
85 | ||
98a3b527 | 86 | Exim will check for a valid next update timestamp in the OCSP proof; |
3f7eeb86 PP |
87 | if not present, or if the proof has expired, it will be ignored. |
88 | ||
89 | At this point in time, we're gathering feedback on use, to determine if | |
90 | it's worth adding complexity to the Exim daemon to periodically re-fetch | |
98a3b527 PP |
91 | OCSP files and somehow handling multiple files. There is no client support |
92 | for OCSP in Exim, this is feature expected to be used by mail clients. | |
3f7eeb86 PP |
93 | |
94 | ||
95 | ||
96 | ||
0b23848a | 97 | Brightmail AntiSpam (BMI) suppport |
ee161e8f PH |
98 | -------------------------------------------------------------- |
99 | ||
100 | Brightmail AntiSpam is a commercial package. Please see | |
101 | http://www.brightmail.com for more information on | |
102 | the product. For the sake of clarity, we'll refer to it as | |
103 | "BMI" from now on. | |
104 | ||
105 | ||
106 | 0) BMI concept and implementation overview | |
107 | ||
108 | In contrast to how spam-scanning with SpamAssassin is | |
109 | implemented in exiscan-acl, BMI is more suited for per | |
110 | -recipient scanning of messages. However, each messages is | |
111 | scanned only once, but multiple "verdicts" for multiple | |
112 | recipients can be returned from the BMI server. The exiscan | |
113 | implementation passes the message to the BMI server just | |
114 | before accepting it. It then adds the retrieved verdicts to | |
115 | the messages header file in the spool. These verdicts can then | |
116 | be queried in routers, where operation is per-recipient | |
117 | instead of per-message. To use BMI, you need to take the | |
118 | following steps: | |
119 | ||
120 | 1) Compile Exim with BMI support | |
3ec3e3bb | 121 | 2) Set up main BMI options (top section of Exim config file) |
ee161e8f PH |
122 | 3) Set up ACL control statement (ACL section of the config |
123 | file) | |
124 | 4) Set up your routers to use BMI verdicts (routers section | |
125 | of the config file). | |
126 | 5) (Optional) Set up per-recipient opt-in information. | |
127 | ||
8ff3788c | 128 | These four steps are explained in more details below. |
ee161e8f PH |
129 | |
130 | 1) Adding support for BMI at compile time | |
131 | ||
132 | To compile with BMI support, you need to link Exim against | |
133 | the Brighmail client SDK, consisting of a library | |
134 | (libbmiclient_single.so) and a header file (bmi_api.h). | |
135 | You'll also need to explicitly set a flag in the Makefile to | |
136 | include BMI support in the Exim binary. Both can be achieved | |
137 | with these lines in Local/Makefile: | |
138 | ||
139 | EXPERIMENTAL_BRIGHTMAIL=yes | |
47bbda99 | 140 | CFLAGS=-I/path/to/the/dir/with/the/includefile |
ee161e8f | 141 | EXTRALIBS_EXIM=-L/path/to/the/dir/with/the/library -lbmiclient_single |
8ff3788c | 142 | |
ee161e8f PH |
143 | If you use other CFLAGS or EXTRALIBS_EXIM settings then |
144 | merge the content of these lines with them. | |
145 | ||
7c0c8547 | 146 | Note for BMI6.x users: You'll also have to add -lxml2_single |
ee161e8f PH |
147 | to the EXTRALIBS_EXIM line. Users of 5.5x do not need to do |
148 | this. | |
8ff3788c | 149 | |
ee161e8f PH |
150 | You should also include the location of |
151 | libbmiclient_single.so in your dynamic linker configuration | |
152 | file (usually /etc/ld.so.conf) and run "ldconfig" | |
153 | afterwards, or else the produced Exim binary will not be | |
154 | able to find the library file. | |
155 | ||
156 | ||
3ec3e3bb | 157 | 2) Setting up BMI support in the Exim main configuration |
ee161e8f | 158 | |
3ec3e3bb | 159 | To enable BMI support in the main Exim configuration, you |
ee161e8f PH |
160 | should set the path to the main BMI configuration file with |
161 | the "bmi_config_file" option, like this: | |
8ff3788c | 162 | |
ee161e8f | 163 | bmi_config_file = /opt/brightmail/etc/brightmail.cfg |
8ff3788c | 164 | |
3ec3e3bb | 165 | This must go into section 1 of Exim's configuration file (You |
ee161e8f PH |
166 | can put it right on top). If you omit this option, it |
167 | defaults to /opt/brightmail/etc/brightmail.cfg. | |
168 | ||
169 | Note for BMI6.x users: This file is in XML format in V6.xx | |
170 | and its name is /opt/brightmail/etc/bmiconfig.xml. So BMI | |
171 | 6.x users MUST set the bmi_config_file option. | |
8ff3788c | 172 | |
ee161e8f PH |
173 | |
174 | 3) Set up ACL control statement | |
175 | ||
176 | To optimize performance, it makes sense only to process | |
177 | messages coming from remote, untrusted sources with the BMI | |
178 | server. To set up a messages for processing by the BMI | |
179 | server, you MUST set the "bmi_run" control statement in any | |
180 | ACL for an incoming message. You will typically do this in | |
181 | an "accept" block in the "acl_check_rcpt" ACL. You should | |
182 | use the "accept" block(s) that accept messages from remote | |
183 | servers for your own domain(s). Here is an example that uses | |
3ec3e3bb | 184 | the "accept" blocks from Exim's default configuration file: |
8ff3788c | 185 | |
ee161e8f PH |
186 | |
187 | accept domains = +local_domains | |
188 | endpass | |
189 | verify = recipient | |
190 | control = bmi_run | |
191 | ||
192 | accept domains = +relay_to_domains | |
193 | endpass | |
194 | verify = recipient | |
195 | control = bmi_run | |
8ff3788c | 196 | |
ee161e8f PH |
197 | If bmi_run is not set in any ACL during reception of the |
198 | message, it will NOT be passed to the BMI server. | |
199 | ||
200 | ||
201 | 4) Setting up routers to use BMI verdicts | |
202 | ||
203 | When a message has been run through the BMI server, one or | |
204 | more "verdicts" are present. Different recipients can have | |
205 | different verdicts. Each recipient is treated individually | |
206 | during routing, so you can query the verdicts by recipient | |
3ec3e3bb | 207 | at that stage. From Exim's view, a verdict can have the |
ee161e8f | 208 | following outcomes: |
8ff3788c | 209 | |
ee161e8f PH |
210 | o deliver the message normally |
211 | o deliver the message to an alternate location | |
212 | o do not deliver the message | |
8ff3788c | 213 | |
ee161e8f PH |
214 | To query the verdict for a recipient, the implementation |
215 | offers the following tools: | |
8ff3788c TK |
216 | |
217 | ||
ee161e8f PH |
218 | - Boolean router preconditions. These can be used in any |
219 | router. For a simple implementation of BMI, these may be | |
220 | all that you need. The following preconditions are | |
221 | available: | |
8ff3788c | 222 | |
ee161e8f | 223 | o bmi_deliver_default |
8ff3788c | 224 | |
ee161e8f PH |
225 | This precondition is TRUE if the verdict for the |
226 | recipient is to deliver the message normally. If the | |
227 | message has not been processed by the BMI server, this | |
228 | variable defaults to TRUE. | |
8ff3788c | 229 | |
ee161e8f | 230 | o bmi_deliver_alternate |
8ff3788c | 231 | |
ee161e8f PH |
232 | This precondition is TRUE if the verdict for the |
233 | recipient is to deliver the message to an alternate | |
234 | location. You can get the location string from the | |
235 | $bmi_alt_location expansion variable if you need it. See | |
236 | further below. If the message has not been processed by | |
237 | the BMI server, this variable defaults to FALSE. | |
8ff3788c | 238 | |
ee161e8f | 239 | o bmi_dont_deliver |
8ff3788c | 240 | |
ee161e8f PH |
241 | This precondition is TRUE if the verdict for the |
242 | recipient is NOT to deliver the message to the | |
243 | recipient. You will typically use this precondition in a | |
244 | top-level blackhole router, like this: | |
8ff3788c | 245 | |
ee161e8f PH |
246 | # don't deliver messages handled by the BMI server |
247 | bmi_blackhole: | |
248 | driver = redirect | |
249 | bmi_dont_deliver | |
250 | data = :blackhole: | |
8ff3788c | 251 | |
ee161e8f PH |
252 | This router should be on top of all others, so messages |
253 | that should not be delivered do not reach other routers | |
254 | at all. If the message has not been processed by | |
255 | the BMI server, this variable defaults to FALSE. | |
8ff3788c TK |
256 | |
257 | ||
ee161e8f PH |
258 | - A list router precondition to query if rules "fired" on |
259 | the message for the recipient. Its name is "bmi_rule". You | |
260 | use it by passing it a colon-separated list of rule | |
261 | numbers. You can use this condition to route messages that | |
262 | matched specific rules. Here is an example: | |
8ff3788c | 263 | |
ee161e8f PH |
264 | # special router for BMI rule #5, #8 and #11 |
265 | bmi_rule_redirect: | |
266 | driver = redirect | |
267 | bmi_rule = 5:8:11 | |
268 | data = postmaster@mydomain.com | |
8ff3788c TK |
269 | |
270 | ||
ee161e8f PH |
271 | - Expansion variables. Several expansion variables are set |
272 | during routing. You can use them in custom router | |
273 | conditions, for example. The following variables are | |
274 | available: | |
8ff3788c | 275 | |
ee161e8f | 276 | o $bmi_base64_verdict |
8ff3788c | 277 | |
ee161e8f PH |
278 | This variable will contain the BASE64 encoded verdict |
279 | for the recipient being routed. You can use it to add a | |
280 | header to messages for tracking purposes, for example: | |
8ff3788c | 281 | |
ee161e8f PH |
282 | localuser: |
283 | driver = accept | |
284 | check_local_user | |
285 | headers_add = X-Brightmail-Verdict: $bmi_base64_verdict | |
286 | transport = local_delivery | |
8ff3788c | 287 | |
ee161e8f PH |
288 | If there is no verdict available for the recipient being |
289 | routed, this variable contains the empty string. | |
8ff3788c | 290 | |
ee161e8f | 291 | o $bmi_base64_tracker_verdict |
8ff3788c | 292 | |
ee161e8f PH |
293 | This variable will contain a BASE64 encoded subset of |
294 | the verdict information concerning the "rules" that | |
295 | fired on the message. You can add this string to a | |
296 | header, commonly named "X-Brightmail-Tracker". Example: | |
8ff3788c | 297 | |
ee161e8f PH |
298 | localuser: |
299 | driver = accept | |
300 | check_local_user | |
301 | headers_add = X-Brightmail-Tracker: $bmi_base64_tracker_verdict | |
302 | transport = local_delivery | |
8ff3788c | 303 | |
ee161e8f PH |
304 | If there is no verdict available for the recipient being |
305 | routed, this variable contains the empty string. | |
8ff3788c | 306 | |
ee161e8f | 307 | o $bmi_alt_location |
8ff3788c | 308 | |
ee161e8f PH |
309 | If the verdict is to redirect the message to an |
310 | alternate location, this variable will contain the | |
311 | alternate location string returned by the BMI server. In | |
312 | its default configuration, this is a header-like string | |
313 | that can be added to the message with "headers_add". If | |
314 | there is no verdict available for the recipient being | |
315 | routed, or if the message is to be delivered normally, | |
316 | this variable contains the empty string. | |
8ff3788c | 317 | |
ee161e8f | 318 | o $bmi_deliver |
8ff3788c | 319 | |
ee161e8f PH |
320 | This is an additional integer variable that can be used |
321 | to query if the message should be delivered at all. You | |
322 | should use router preconditions instead if possible. | |
8ff3788c | 323 | |
ee161e8f PH |
324 | $bmi_deliver is '0': the message should NOT be delivered. |
325 | $bmi_deliver is '1': the message should be delivered. | |
8ff3788c TK |
326 | |
327 | ||
ee161e8f PH |
328 | IMPORTANT NOTE: Verdict inheritance. |
329 | The message is passed to the BMI server during message | |
330 | reception, using the target addresses from the RCPT TO: | |
331 | commands in the SMTP transaction. If recipients get expanded | |
332 | or re-written (for example by aliasing), the new address(es) | |
333 | inherit the verdict from the original address. This means | |
334 | that verdicts also apply to all "child" addresses generated | |
335 | from top-level addresses that were sent to the BMI server. | |
8ff3788c TK |
336 | |
337 | ||
ee161e8f PH |
338 | 5) Using per-recipient opt-in information (Optional) |
339 | ||
340 | The BMI server features multiple scanning "profiles" for | |
341 | individual recipients. These are usually stored in a LDAP | |
342 | server and are queried by the BMI server itself. However, | |
343 | you can also pass opt-in data for each recipient from the | |
344 | MTA to the BMI server. This is particularly useful if you | |
3ec3e3bb | 345 | already look up recipient data in Exim anyway (which can |
ee161e8f PH |
346 | also be stored in a SQL database or other source). This |
347 | implementation enables you to pass opt-in data to the BMI | |
348 | server in the RCPT ACL. This works by setting the | |
349 | 'bmi_optin' modifier in a block of that ACL. If should be | |
350 | set to a list of comma-separated strings that identify the | |
351 | features which the BMI server should use for that particular | |
352 | recipient. Ideally, you would use the 'bmi_optin' modifier | |
353 | in the same ACL block where you set the 'bmi_run' control | |
354 | flag. Here is an example that will pull opt-in data for each | |
355 | recipient from a flat file called | |
356 | '/etc/exim/bmi_optin_data'. | |
8ff3788c | 357 | |
ee161e8f | 358 | The file format: |
8ff3788c | 359 | |
ee161e8f PH |
360 | user1@mydomain.com: <OPTIN STRING1>:<OPTIN STRING2> |
361 | user2@thatdomain.com: <OPTIN STRING3> | |
8ff3788c TK |
362 | |
363 | ||
ee161e8f | 364 | The example: |
8ff3788c | 365 | |
ee161e8f PH |
366 | accept domains = +relay_to_domains |
367 | endpass | |
368 | verify = recipient | |
369 | bmi_optin = ${lookup{$local_part@$domain}lsearch{/etc/exim/bmi_optin_data}} | |
8ff3788c TK |
370 | control = bmi_run |
371 | ||
ee161e8f | 372 | Of course, you can also use any other lookup method that |
3ec3e3bb | 373 | Exim supports, including LDAP, Postgres, MySQL, Oracle etc., |
ee161e8f PH |
374 | as long as the result is a list of colon-separated opt-in |
375 | strings. | |
8ff3788c | 376 | |
ee161e8f PH |
377 | For a list of available opt-in strings, please contact your |
378 | Brightmail representative. | |
ee161e8f | 379 | |
8ff3788c TK |
380 | |
381 | ||
382 | ||
0b23848a | 383 | Sender Policy Framework (SPF) support |
ee161e8f PH |
384 | -------------------------------------------------------------- |
385 | ||
f413481d | 386 | To learn more about SPF, visit http://www.openspf.org. This |
ee161e8f PH |
387 | document does not explain the SPF fundamentals, you should |
388 | read and understand the implications of deploying SPF on your | |
389 | system before doing so. | |
390 | ||
8ff3788c | 391 | SPF support is added via the libspf2 library. Visit |
ee161e8f PH |
392 | |
393 | http://www.libspf2.org/ | |
8ff3788c | 394 | |
ee161e8f PH |
395 | to obtain a copy, then compile and install it. By default, |
396 | this will put headers in /usr/local/include and the static | |
397 | library in /usr/local/lib. | |
398 | ||
3ec3e3bb | 399 | To compile Exim with SPF support, set these additional flags in |
ee161e8f PH |
400 | Local/Makefile: |
401 | ||
402 | EXPERIMENTAL_SPF=yes | |
403 | CFLAGS=-DSPF -I/usr/local/include | |
404 | EXTRALIBS_EXIM=-L/usr/local/lib -lspf2 | |
405 | ||
406 | This assumes that the libspf2 files are installed in | |
407 | their default locations. | |
408 | ||
409 | You can now run SPF checks in incoming SMTP by using the "spf" | |
410 | ACL condition in either the MAIL, RCPT or DATA ACLs. When | |
d36a0501 | 411 | using it in the RCPT ACL, you can make the checks dependent on |
ee161e8f PH |
412 | the RCPT address (or domain), so you can check SPF records |
413 | only for certain target domains. This gives you the | |
414 | possibility to opt-out certain customers that do not want | |
415 | their mail to be subject to SPF checking. | |
416 | ||
417 | The spf condition takes a list of strings on its right-hand | |
418 | side. These strings describe the outcome of the SPF check for | |
419 | which the spf condition should succeed. Valid strings are: | |
420 | ||
421 | o pass The SPF check passed, the sending host | |
422 | is positively verified by SPF. | |
423 | o fail The SPF check failed, the sending host | |
424 | is NOT allowed to send mail for the domain | |
425 | in the envelope-from address. | |
426 | o softfail The SPF check failed, but the queried | |
427 | domain can't absolutely confirm that this | |
428 | is a forgery. | |
429 | o none The queried domain does not publish SPF | |
430 | records. | |
431 | o neutral The SPF check returned a "neutral" state. | |
432 | This means the queried domain has published | |
433 | a SPF record, but wants to allow outside | |
434 | servers to send mail under its domain as well. | |
435 | o err_perm This indicates a syntax error in the SPF | |
436 | record of the queried domain. This should be | |
437 | treated like "none". | |
438 | o err_temp This indicates a temporary error during all | |
3ec3e3bb | 439 | processing, including Exim's SPF processing. |
ee161e8f | 440 | You may defer messages when this occurs. |
8ff3788c | 441 | |
ee161e8f PH |
442 | You can prefix each string with an exclamation mark to invert |
443 | is meaning, for example "!fail" will match all results but | |
444 | "fail". The string list is evaluated left-to-right, in a | |
445 | short-circuit fashion. When a string matches the outcome of | |
446 | the SPF check, the condition succeeds. If none of the listed | |
447 | strings matches the outcome of the SPF check, the condition | |
448 | fails. | |
449 | ||
f413481d TK |
450 | Here is an example to fail forgery attempts from domains that |
451 | publish SPF records: | |
ee161e8f PH |
452 | |
453 | /* ----------------- | |
f413481d TK |
454 | deny message = $sender_host_address is not allowed to send mail from ${if def:sender_address_domain {$sender_address_domain}{$sender_helo_name}}. \ |
455 | Please see http://www.openspf.org/Why?scope=${if def:sender_address_domain {mfrom}{helo}};identity=${if def:sender_address_domain {$sender_address}{$sender_helo_name}};ip=$sender_host_address | |
ee161e8f PH |
456 | spf = fail |
457 | --------------------- */ | |
458 | ||
459 | You can also give special treatment to specific domains: | |
460 | ||
461 | /* ----------------- | |
462 | deny message = AOL sender, but not from AOL-approved relay. | |
463 | sender_domains = aol.com | |
464 | spf = fail:neutral | |
465 | --------------------- */ | |
466 | ||
467 | Explanation: AOL publishes SPF records, but is liberal and | |
468 | still allows non-approved relays to send mail from aol.com. | |
469 | This will result in a "neutral" state, while mail from genuine | |
470 | AOL servers will result in "pass". The example above takes | |
471 | this into account and treats "neutral" like "fail", but only | |
472 | for aol.com. Please note that this violates the SPF draft. | |
473 | ||
474 | When the spf condition has run, it sets up several expansion | |
475 | variables. | |
476 | ||
477 | $spf_header_comment | |
478 | This contains a human-readable string describing the outcome | |
479 | of the SPF check. You can add it to a custom header or use | |
480 | it for logging purposes. | |
8ff3788c | 481 | |
ee161e8f | 482 | $spf_received |
8fe685ad | 483 | This contains a complete Received-SPF: header that can be |
ee161e8f PH |
484 | added to the message. Please note that according to the SPF |
485 | draft, this header must be added at the top of the header | |
486 | list. Please see section 10 on how you can do this. | |
8ff3788c | 487 | |
65a7d8c3 NM |
488 | Note: in case of "Best-guess" (see below), the convention is |
489 | to put this string in a header called X-SPF-Guess: instead. | |
490 | ||
ee161e8f PH |
491 | $spf_result |
492 | This contains the outcome of the SPF check in string form, | |
493 | one of pass, fail, softfail, none, neutral, err_perm or | |
494 | err_temp. | |
8ff3788c | 495 | |
ee161e8f PH |
496 | $spf_smtp_comment |
497 | This contains a string that can be used in a SMTP response | |
498 | to the calling party. Useful for "fail". | |
8ff3788c | 499 | |
65a7d8c3 NM |
500 | In addition to SPF, you can also perform checks for so-called |
501 | "Best-guess". Strictly speaking, "Best-guess" is not standard | |
502 | SPF, but it is supported by the same framework that enables SPF | |
503 | capability. Refer to http://www.openspf.org/FAQ/Best_guess_record | |
504 | for a description of what it means. | |
505 | ||
506 | To access this feature, simply use the spf_guess condition in place | |
507 | of the spf one. For example: | |
508 | ||
509 | /* ----------------- | |
510 | deny message = $sender_host_address doesn't look trustworthy to me | |
511 | spf_guess = fail | |
512 | --------------------- */ | |
513 | ||
514 | In case you decide to reject messages based on this check, you | |
515 | should note that although it uses the same framework, "Best-guess" | |
516 | is NOT SPF, and therefore you should not mention SPF at all in your | |
517 | reject message. | |
518 | ||
519 | When the spf_guess condition has run, it sets up the same expansion | |
520 | variables as when spf condition is run, described above. | |
521 | ||
d36a0501 | 522 | Additionally, since Best-guess is not standardized, you may redefine |
65a7d8c3 NM |
523 | what "Best-guess" means to you by redefining spf_guess variable in |
524 | global config. For example, the following: | |
525 | ||
526 | /* ----------------- | |
527 | spf_guess = v=spf1 a/16 mx/16 ptr ?all | |
528 | --------------------- */ | |
529 | ||
530 | would relax host matching rules to a broader network range. | |
8ff3788c | 531 | |
ee161e8f | 532 | |
0b23848a | 533 | SRS (Sender Rewriting Scheme) Support |
ee161e8f PH |
534 | -------------------------------------------------------------- |
535 | ||
536 | Exiscan currently includes SRS support via Miles Wilton's | |
8ff3788c | 537 | libsrs_alt library. The current version of the supported |
ee161e8f PH |
538 | library is 0.5. |
539 | ||
540 | In order to use SRS, you must get a copy of libsrs_alt from | |
541 | ||
542 | http://srs.mirtol.com/ | |
543 | ||
544 | Unpack the tarball, then refer to MTAs/README.EXIM | |
545 | to proceed. You need to set | |
546 | ||
547 | EXPERIMENTAL_SRS=yes | |
548 | ||
549 | in your Local/Makefile. | |
550 | ||
551 | ||
0e1ccf44 PP |
552 | DCC Support |
553 | -------------------------------------------------------------- | |
554 | ||
555 | *) Building exim | |
556 | ||
557 | In order to build exim with DCC support add | |
558 | ||
559 | EXPERIMENTAL_DCC=yes | |
560 | ||
561 | to your Makefile. (Re-)build/install exim. exim -d should show | |
562 | EXPERIMENTAL_DCC under "Support for". | |
563 | ||
564 | ||
565 | *) Configuration | |
566 | ||
567 | In the main section of exim.cf add at least | |
568 | dccifd_address = /usr/local/dcc/var/dccifd | |
569 | or | |
570 | dccifd_address = <ip> <port> | |
571 | ||
572 | In the DATA ACL you can use the new condition | |
573 | dcc = * | |
574 | ||
575 | After that "$dcc_header" contains the X-DCC-Header. | |
576 | ||
d36a0501 | 577 | Return values are: |
0e1ccf44 PP |
578 | fail for overall "R", "G" from dccifd |
579 | defer for overall "T" from dccifd | |
580 | accept for overall "A", "S" from dccifd | |
581 | ||
582 | dcc = */defer_ok works as for spamd. | |
583 | ||
584 | The "$dcc_result" variable contains the overall result from DCC | |
585 | answer. There will an X-DCC: header added to the mail. | |
586 | ||
587 | Usually you'll use | |
588 | defer !dcc = * | |
589 | to greylist with DCC. | |
590 | ||
591 | If you set, in the main section, | |
592 | dcc_direct_add_header = true | |
593 | then the dcc header will be added "in deep" and if the spool | |
594 | file was already written it gets removed. This forces Exim to | |
595 | write it again if needed. This helps to get the DCC Header | |
596 | through to eg. SpamAssassin. | |
597 | ||
598 | If you want to pass even more headers in the middle of the | |
599 | DATA stage you can set | |
600 | $acl_m_dcc_add_header | |
05c39afa | 601 | to tell the DCC routines to add more information; eg, you might set |
0e1ccf44 PP |
602 | this to some results from ClamAV. Be careful. Header syntax is |
603 | not checked and is added "as is". | |
604 | ||
05c39afa JH |
605 | In case you've troubles with sites sending the same queue items from several |
606 | hosts and fail to get through greylisting you can use | |
607 | $acl_m_dcc_override_client_ip | |
608 | ||
609 | Setting $acl_m_dcc_override_client_ip to an IP address overrides the default | |
610 | of $sender_host_address. eg. use the following ACL in DATA stage: | |
611 | ||
612 | warn set acl_m_dcc_override_client_ip = \ | |
613 | ${lookup{$sender_helo_name}nwildlsearch{/etc/mail/multipleip_sites}{$value}{}} | |
614 | condition = ${if def:acl_m_dcc_override_client_ip} | |
615 | log_message = dbg: acl_m_dcc_override_client_ip set to \ | |
616 | $acl_m_dcc_override_client_ip | |
617 | ||
618 | Then set something like | |
619 | # cat /etc/mail/multipleip_sites | |
620 | mout-xforward.gmx.net 82.165.159.12 | |
621 | mout.gmx.net 212.227.15.16 | |
622 | ||
623 | Use a reasonable IP. eg. one the sending cluster acutally uses. | |
0e1ccf44 | 624 | |
ee161e8f PH |
625 | -------------------------------------------------------------- |
626 | End of file | |
627 | -------------------------------------------------------------- |