Diffs for draft 11
[exim.git] / doc / doc-txt / experimental-spec.txt
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1From time to time, experimental features may be added to Exim.
2While a feature is experimental, there will be a build-time
3option whose name starts "EXPERIMENTAL_" that must be set in
4order to include the feature. This file contains information
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5about experimental features, all of which are unstable and
6liable to incompatible change.
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7
8
0b23848a 9Brightmail AntiSpam (BMI) suppport
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10--------------------------------------------------------------
11
12Brightmail AntiSpam is a commercial package. Please see
13http://www.brightmail.com for more information on
14the product. For the sake of clarity, we'll refer to it as
15"BMI" from now on.
16
17
180) BMI concept and implementation overview
19
20In contrast to how spam-scanning with SpamAssassin is
21implemented in exiscan-acl, BMI is more suited for per
22-recipient scanning of messages. However, each messages is
23scanned only once, but multiple "verdicts" for multiple
24recipients can be returned from the BMI server. The exiscan
25implementation passes the message to the BMI server just
26before accepting it. It then adds the retrieved verdicts to
27the messages header file in the spool. These verdicts can then
28be queried in routers, where operation is per-recipient
29instead of per-message. To use BMI, you need to take the
30following steps:
31
32 1) Compile Exim with BMI support
3ec3e3bb 33 2) Set up main BMI options (top section of Exim config file)
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34 3) Set up ACL control statement (ACL section of the config
35 file)
36 4) Set up your routers to use BMI verdicts (routers section
37 of the config file).
38 5) (Optional) Set up per-recipient opt-in information.
39
8ff3788c 40These four steps are explained in more details below.
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41
421) Adding support for BMI at compile time
43
44 To compile with BMI support, you need to link Exim against
45 the Brighmail client SDK, consisting of a library
46 (libbmiclient_single.so) and a header file (bmi_api.h).
47 You'll also need to explicitly set a flag in the Makefile to
48 include BMI support in the Exim binary. Both can be achieved
49 with these lines in Local/Makefile:
50
51 EXPERIMENTAL_BRIGHTMAIL=yes
47bbda99 52 CFLAGS=-I/path/to/the/dir/with/the/includefile
ee161e8f 53 EXTRALIBS_EXIM=-L/path/to/the/dir/with/the/library -lbmiclient_single
8ff3788c 54
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55 If you use other CFLAGS or EXTRALIBS_EXIM settings then
56 merge the content of these lines with them.
57
7c0c8547 58 Note for BMI6.x users: You'll also have to add -lxml2_single
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59 to the EXTRALIBS_EXIM line. Users of 5.5x do not need to do
60 this.
8ff3788c 61
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62 You should also include the location of
63 libbmiclient_single.so in your dynamic linker configuration
64 file (usually /etc/ld.so.conf) and run "ldconfig"
65 afterwards, or else the produced Exim binary will not be
66 able to find the library file.
67
68
3ec3e3bb 692) Setting up BMI support in the Exim main configuration
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3ec3e3bb 71 To enable BMI support in the main Exim configuration, you
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72 should set the path to the main BMI configuration file with
73 the "bmi_config_file" option, like this:
8ff3788c 74
ee161e8f 75 bmi_config_file = /opt/brightmail/etc/brightmail.cfg
8ff3788c 76
3ec3e3bb 77 This must go into section 1 of Exim's configuration file (You
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78 can put it right on top). If you omit this option, it
79 defaults to /opt/brightmail/etc/brightmail.cfg.
80
81 Note for BMI6.x users: This file is in XML format in V6.xx
82 and its name is /opt/brightmail/etc/bmiconfig.xml. So BMI
83 6.x users MUST set the bmi_config_file option.
8ff3788c 84
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85
863) Set up ACL control statement
87
88 To optimize performance, it makes sense only to process
89 messages coming from remote, untrusted sources with the BMI
90 server. To set up a messages for processing by the BMI
91 server, you MUST set the "bmi_run" control statement in any
92 ACL for an incoming message. You will typically do this in
93 an "accept" block in the "acl_check_rcpt" ACL. You should
94 use the "accept" block(s) that accept messages from remote
95 servers for your own domain(s). Here is an example that uses
3ec3e3bb 96 the "accept" blocks from Exim's default configuration file:
8ff3788c 97
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98
99 accept domains = +local_domains
100 endpass
101 verify = recipient
102 control = bmi_run
103
104 accept domains = +relay_to_domains
105 endpass
106 verify = recipient
107 control = bmi_run
8ff3788c 108
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109 If bmi_run is not set in any ACL during reception of the
110 message, it will NOT be passed to the BMI server.
111
112
1134) Setting up routers to use BMI verdicts
114
115 When a message has been run through the BMI server, one or
116 more "verdicts" are present. Different recipients can have
117 different verdicts. Each recipient is treated individually
118 during routing, so you can query the verdicts by recipient
3ec3e3bb 119 at that stage. From Exim's view, a verdict can have the
ee161e8f 120 following outcomes:
8ff3788c 121
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122 o deliver the message normally
123 o deliver the message to an alternate location
124 o do not deliver the message
8ff3788c 125
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126 To query the verdict for a recipient, the implementation
127 offers the following tools:
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128
129
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130 - Boolean router preconditions. These can be used in any
131 router. For a simple implementation of BMI, these may be
132 all that you need. The following preconditions are
133 available:
8ff3788c 134
ee161e8f 135 o bmi_deliver_default
8ff3788c 136
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137 This precondition is TRUE if the verdict for the
138 recipient is to deliver the message normally. If the
139 message has not been processed by the BMI server, this
140 variable defaults to TRUE.
8ff3788c 141
ee161e8f 142 o bmi_deliver_alternate
8ff3788c 143
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144 This precondition is TRUE if the verdict for the
145 recipient is to deliver the message to an alternate
146 location. You can get the location string from the
147 $bmi_alt_location expansion variable if you need it. See
148 further below. If the message has not been processed by
149 the BMI server, this variable defaults to FALSE.
8ff3788c 150
ee161e8f 151 o bmi_dont_deliver
8ff3788c 152
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153 This precondition is TRUE if the verdict for the
154 recipient is NOT to deliver the message to the
155 recipient. You will typically use this precondition in a
156 top-level blackhole router, like this:
8ff3788c 157
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158 # don't deliver messages handled by the BMI server
159 bmi_blackhole:
160 driver = redirect
161 bmi_dont_deliver
162 data = :blackhole:
8ff3788c 163
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164 This router should be on top of all others, so messages
165 that should not be delivered do not reach other routers
166 at all. If the message has not been processed by
167 the BMI server, this variable defaults to FALSE.
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168
169
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170 - A list router precondition to query if rules "fired" on
171 the message for the recipient. Its name is "bmi_rule". You
172 use it by passing it a colon-separated list of rule
173 numbers. You can use this condition to route messages that
174 matched specific rules. Here is an example:
8ff3788c 175
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176 # special router for BMI rule #5, #8 and #11
177 bmi_rule_redirect:
178 driver = redirect
179 bmi_rule = 5:8:11
180 data = postmaster@mydomain.com
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181
182
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183 - Expansion variables. Several expansion variables are set
184 during routing. You can use them in custom router
185 conditions, for example. The following variables are
186 available:
8ff3788c 187
ee161e8f 188 o $bmi_base64_verdict
8ff3788c 189
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190 This variable will contain the BASE64 encoded verdict
191 for the recipient being routed. You can use it to add a
192 header to messages for tracking purposes, for example:
8ff3788c 193
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194 localuser:
195 driver = accept
196 check_local_user
197 headers_add = X-Brightmail-Verdict: $bmi_base64_verdict
198 transport = local_delivery
8ff3788c 199
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200 If there is no verdict available for the recipient being
201 routed, this variable contains the empty string.
8ff3788c 202
ee161e8f 203 o $bmi_base64_tracker_verdict
8ff3788c 204
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205 This variable will contain a BASE64 encoded subset of
206 the verdict information concerning the "rules" that
207 fired on the message. You can add this string to a
208 header, commonly named "X-Brightmail-Tracker". Example:
8ff3788c 209
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210 localuser:
211 driver = accept
212 check_local_user
213 headers_add = X-Brightmail-Tracker: $bmi_base64_tracker_verdict
214 transport = local_delivery
8ff3788c 215
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216 If there is no verdict available for the recipient being
217 routed, this variable contains the empty string.
8ff3788c 218
ee161e8f 219 o $bmi_alt_location
8ff3788c 220
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221 If the verdict is to redirect the message to an
222 alternate location, this variable will contain the
223 alternate location string returned by the BMI server. In
224 its default configuration, this is a header-like string
225 that can be added to the message with "headers_add". If
226 there is no verdict available for the recipient being
227 routed, or if the message is to be delivered normally,
228 this variable contains the empty string.
8ff3788c 229
ee161e8f 230 o $bmi_deliver
8ff3788c 231
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232 This is an additional integer variable that can be used
233 to query if the message should be delivered at all. You
234 should use router preconditions instead if possible.
8ff3788c 235
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236 $bmi_deliver is '0': the message should NOT be delivered.
237 $bmi_deliver is '1': the message should be delivered.
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238
239
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240 IMPORTANT NOTE: Verdict inheritance.
241 The message is passed to the BMI server during message
242 reception, using the target addresses from the RCPT TO:
243 commands in the SMTP transaction. If recipients get expanded
244 or re-written (for example by aliasing), the new address(es)
245 inherit the verdict from the original address. This means
246 that verdicts also apply to all "child" addresses generated
247 from top-level addresses that were sent to the BMI server.
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248
249
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2505) Using per-recipient opt-in information (Optional)
251
252 The BMI server features multiple scanning "profiles" for
253 individual recipients. These are usually stored in a LDAP
254 server and are queried by the BMI server itself. However,
255 you can also pass opt-in data for each recipient from the
256 MTA to the BMI server. This is particularly useful if you
3ec3e3bb 257 already look up recipient data in Exim anyway (which can
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258 also be stored in a SQL database or other source). This
259 implementation enables you to pass opt-in data to the BMI
260 server in the RCPT ACL. This works by setting the
261 'bmi_optin' modifier in a block of that ACL. If should be
262 set to a list of comma-separated strings that identify the
263 features which the BMI server should use for that particular
264 recipient. Ideally, you would use the 'bmi_optin' modifier
265 in the same ACL block where you set the 'bmi_run' control
266 flag. Here is an example that will pull opt-in data for each
267 recipient from a flat file called
268 '/etc/exim/bmi_optin_data'.
8ff3788c 269
ee161e8f 270 The file format:
8ff3788c 271
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272 user1@mydomain.com: <OPTIN STRING1>:<OPTIN STRING2>
273 user2@thatdomain.com: <OPTIN STRING3>
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274
275
ee161e8f 276 The example:
8ff3788c 277
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278 accept domains = +relay_to_domains
279 endpass
280 verify = recipient
281 bmi_optin = ${lookup{$local_part@$domain}lsearch{/etc/exim/bmi_optin_data}}
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282 control = bmi_run
283
ee161e8f 284 Of course, you can also use any other lookup method that
3ec3e3bb 285 Exim supports, including LDAP, Postgres, MySQL, Oracle etc.,
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286 as long as the result is a list of colon-separated opt-in
287 strings.
8ff3788c 288
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289 For a list of available opt-in strings, please contact your
290 Brightmail representative.
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292
293
294
0b23848a 295Sender Policy Framework (SPF) support
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296--------------------------------------------------------------
297
f413481d 298To learn more about SPF, visit http://www.openspf.org. This
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299document does not explain the SPF fundamentals, you should
300read and understand the implications of deploying SPF on your
301system before doing so.
302
8ff3788c 303SPF support is added via the libspf2 library. Visit
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304
305 http://www.libspf2.org/
8ff3788c 306
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307to obtain a copy, then compile and install it. By default,
308this will put headers in /usr/local/include and the static
309library in /usr/local/lib.
310
3ec3e3bb 311To compile Exim with SPF support, set these additional flags in
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312Local/Makefile:
313
314EXPERIMENTAL_SPF=yes
315CFLAGS=-DSPF -I/usr/local/include
316EXTRALIBS_EXIM=-L/usr/local/lib -lspf2
317
318This assumes that the libspf2 files are installed in
319their default locations.
320
321You can now run SPF checks in incoming SMTP by using the "spf"
322ACL condition in either the MAIL, RCPT or DATA ACLs. When
d36a0501 323using it in the RCPT ACL, you can make the checks dependent on
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324the RCPT address (or domain), so you can check SPF records
325only for certain target domains. This gives you the
326possibility to opt-out certain customers that do not want
327their mail to be subject to SPF checking.
328
329The spf condition takes a list of strings on its right-hand
330side. These strings describe the outcome of the SPF check for
331which the spf condition should succeed. Valid strings are:
332
333 o pass The SPF check passed, the sending host
334 is positively verified by SPF.
335 o fail The SPF check failed, the sending host
336 is NOT allowed to send mail for the domain
337 in the envelope-from address.
338 o softfail The SPF check failed, but the queried
339 domain can't absolutely confirm that this
340 is a forgery.
341 o none The queried domain does not publish SPF
342 records.
343 o neutral The SPF check returned a "neutral" state.
344 This means the queried domain has published
345 a SPF record, but wants to allow outside
346 servers to send mail under its domain as well.
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347 This should be treated like "none".
348 o permerror This indicates a syntax error in the SPF
349 record of the queried domain. You may deny
350 messages when this occurs. (Changed in 4.83)
351 o temperror This indicates a temporary error during all
3ec3e3bb 352 processing, including Exim's SPF processing.
ee161e8f 353 You may defer messages when this occurs.
8ddef691 354 (Changed in 4.83)
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355 o err_temp Same as permerror, deprecated in 4.83, will be
356 removed in a future release.
357 o err_perm Same as temperror, deprecated in 4.83, will be
358 removed in a future release.
8ff3788c 359
ee161e8f 360You can prefix each string with an exclamation mark to invert
982650ec 361its meaning, for example "!fail" will match all results but
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362"fail". The string list is evaluated left-to-right, in a
363short-circuit fashion. When a string matches the outcome of
364the SPF check, the condition succeeds. If none of the listed
365strings matches the outcome of the SPF check, the condition
366fails.
367
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368Here is an example to fail forgery attempts from domains that
369publish SPF records:
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370
371/* -----------------
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372deny message = $sender_host_address is not allowed to send mail from ${if def:sender_address_domain {$sender_address_domain}{$sender_helo_name}}. \
373 Please see http://www.openspf.org/Why?scope=${if def:sender_address_domain {mfrom}{helo}};identity=${if def:sender_address_domain {$sender_address}{$sender_helo_name}};ip=$sender_host_address
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374 spf = fail
375--------------------- */
376
377You can also give special treatment to specific domains:
378
379/* -----------------
380deny message = AOL sender, but not from AOL-approved relay.
381 sender_domains = aol.com
382 spf = fail:neutral
383--------------------- */
384
385Explanation: AOL publishes SPF records, but is liberal and
386still allows non-approved relays to send mail from aol.com.
387This will result in a "neutral" state, while mail from genuine
388AOL servers will result in "pass". The example above takes
389this into account and treats "neutral" like "fail", but only
390for aol.com. Please note that this violates the SPF draft.
391
392When the spf condition has run, it sets up several expansion
393variables.
394
395 $spf_header_comment
396 This contains a human-readable string describing the outcome
397 of the SPF check. You can add it to a custom header or use
398 it for logging purposes.
8ff3788c 399
ee161e8f 400 $spf_received
8fe685ad 401 This contains a complete Received-SPF: header that can be
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402 added to the message. Please note that according to the SPF
403 draft, this header must be added at the top of the header
404 list. Please see section 10 on how you can do this.
8ff3788c 405
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406 Note: in case of "Best-guess" (see below), the convention is
407 to put this string in a header called X-SPF-Guess: instead.
408
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409 $spf_result
410 This contains the outcome of the SPF check in string form,
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411 one of pass, fail, softfail, none, neutral, permerror or
412 temperror.
8ff3788c 413
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414 $spf_smtp_comment
415 This contains a string that can be used in a SMTP response
416 to the calling party. Useful for "fail".
8ff3788c 417
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418In addition to SPF, you can also perform checks for so-called
419"Best-guess". Strictly speaking, "Best-guess" is not standard
420SPF, but it is supported by the same framework that enables SPF
421capability. Refer to http://www.openspf.org/FAQ/Best_guess_record
422for a description of what it means.
423
424To access this feature, simply use the spf_guess condition in place
425of the spf one. For example:
426
427/* -----------------
428deny message = $sender_host_address doesn't look trustworthy to me
429 spf_guess = fail
430--------------------- */
431
432In case you decide to reject messages based on this check, you
433should note that although it uses the same framework, "Best-guess"
434is NOT SPF, and therefore you should not mention SPF at all in your
435reject message.
436
437When the spf_guess condition has run, it sets up the same expansion
438variables as when spf condition is run, described above.
439
d36a0501 440Additionally, since Best-guess is not standardized, you may redefine
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441what "Best-guess" means to you by redefining spf_guess variable in
442global config. For example, the following:
443
444/* -----------------
445spf_guess = v=spf1 a/16 mx/16 ptr ?all
446--------------------- */
447
448would relax host matching rules to a broader network range.
8ff3788c 449
ee161e8f 450
0b23848a 451SRS (Sender Rewriting Scheme) Support
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452--------------------------------------------------------------
453
454Exiscan currently includes SRS support via Miles Wilton's
8ff3788c 455libsrs_alt library. The current version of the supported
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456library is 0.5.
457
458In order to use SRS, you must get a copy of libsrs_alt from
459
460http://srs.mirtol.com/
461
462Unpack the tarball, then refer to MTAs/README.EXIM
463to proceed. You need to set
464
465EXPERIMENTAL_SRS=yes
466
467in your Local/Makefile.
468
469
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470DCC Support
471--------------------------------------------------------------
472
473*) Building exim
474
475In order to build exim with DCC support add
476
477EXPERIMENTAL_DCC=yes
478
479to your Makefile. (Re-)build/install exim. exim -d should show
480EXPERIMENTAL_DCC under "Support for".
481
482
483*) Configuration
484
485In the main section of exim.cf add at least
486 dccifd_address = /usr/local/dcc/var/dccifd
487or
488 dccifd_address = <ip> <port>
489
490In the DATA ACL you can use the new condition
491 dcc = *
492
493After that "$dcc_header" contains the X-DCC-Header.
494
d36a0501 495Return values are:
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496 fail for overall "R", "G" from dccifd
497 defer for overall "T" from dccifd
498 accept for overall "A", "S" from dccifd
499
500dcc = */defer_ok works as for spamd.
501
502The "$dcc_result" variable contains the overall result from DCC
503answer. There will an X-DCC: header added to the mail.
504
505Usually you'll use
506 defer !dcc = *
507to greylist with DCC.
508
509If you set, in the main section,
510 dcc_direct_add_header = true
511then the dcc header will be added "in deep" and if the spool
512file was already written it gets removed. This forces Exim to
513write it again if needed. This helps to get the DCC Header
514through to eg. SpamAssassin.
515
516If you want to pass even more headers in the middle of the
517DATA stage you can set
518 $acl_m_dcc_add_header
05c39afa 519to tell the DCC routines to add more information; eg, you might set
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520this to some results from ClamAV. Be careful. Header syntax is
521not checked and is added "as is".
522
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523In case you've troubles with sites sending the same queue items from several
524hosts and fail to get through greylisting you can use
525$acl_m_dcc_override_client_ip
526
527Setting $acl_m_dcc_override_client_ip to an IP address overrides the default
528of $sender_host_address. eg. use the following ACL in DATA stage:
529
530 warn set acl_m_dcc_override_client_ip = \
531 ${lookup{$sender_helo_name}nwildlsearch{/etc/mail/multipleip_sites}{$value}{}}
532 condition = ${if def:acl_m_dcc_override_client_ip}
533 log_message = dbg: acl_m_dcc_override_client_ip set to \
534 $acl_m_dcc_override_client_ip
535
536Then set something like
537# cat /etc/mail/multipleip_sites
538mout-xforward.gmx.net 82.165.159.12
539mout.gmx.net 212.227.15.16
540
541Use a reasonable IP. eg. one the sending cluster acutally uses.
0e1ccf44 542
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543DMARC Support
544--------------------------------------------------------------
545
546DMARC combines feedback from SPF, DKIM, and header From: in order
547to attempt to provide better indicators of the authenticity of an
548email. This document does not explain the fundamentals, you
549should read and understand how it works by visiting the website at
550http://www.dmarc.org/.
551
552DMARC support is added via the libopendmarc library. Visit:
553
554 http://sourceforge.net/projects/opendmarc/
555
556to obtain a copy, or find it in your favorite rpm package
557repository. If building from source, this description assumes
558that headers will be in /usr/local/include, and that the libraries
559are in /usr/local/lib.
560
5611. To compile Exim with DMARC support, you must first enable SPF.
562Please read the above section on enabling the EXPERIMENTAL_SPF
563feature. You must also have DKIM support, so you cannot set the
564DISABLE_DKIM feature. Once both of those conditions have been met
565you can enable DMARC in Local/Makefile:
566
567EXPERIMENTAL_DMARC=yes
568LDFLAGS += -lopendmarc
569# CFLAGS += -I/usr/local/include
570# LDFLAGS += -L/usr/local/lib
571
572The first line sets the feature to include the correct code, and
573the second line says to link the libopendmarc libraries into the
574exim binary. The commented out lines should be uncommented if you
575built opendmarc from source and installed in the default location.
576Adjust the paths if you installed them elsewhere, but you do not
577need to uncomment them if an rpm (or you) installed them in the
578package controlled locations (/usr/include and /usr/lib).
579
580
5812. Use the following global settings to configure DMARC:
582
583Required:
584dmarc_tld_file Defines the location of a text file of valid
585 top level domains the opendmarc library uses
586 during domain parsing. Maintained by Mozilla,
587 the most current version can be downloaded
588 from a link at http://publicsuffix.org/list/.
589
590Optional:
591dmarc_history_file Defines the location of a file to log results
592 of dmarc verification on inbound emails. The
593 contents are importable by the opendmarc tools
594 which will manage the data, send out DMARC
595 reports, and expire the data. Make sure the
596 directory of this file is writable by the user
597 exim runs as.
598
599dmarc_forensic_sender The email address to use when sending a
600 forensic report detailing alignment failures
601 if a sender domain's dmarc record specifies it
602 and you have configured Exim to send them.
603 Default: do-not-reply@$default_hostname
604
605
6063. By default, the DMARC processing will run for any remote,
607non-authenticated user. It makes sense to only verify DMARC
608status of messages coming from remote, untrusted sources. You can
609use standard conditions such as hosts, senders, etc, to decide that
610DMARC verification should *not* be performed for them and disable
611DMARC with a control setting:
612
12d0043d 613 control = dmarc_disable_verify
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614
615A DMARC record can also specify a "forensic address", which gives
616exim an email address to submit reports about failed alignment.
617Exim does not do this by default because in certain conditions it
618results in unintended information leakage (what lists a user might
619be subscribed to, etc). You must configure exim to submit forensic
620reports to the owner of the domain. If the DMARC record contains a
621forensic address and you specify the control statement below, then
622exim will send these forensic emails. It's also advised that you
623configure a dmarc_forensic_sender because the default sender address
624construction might be inadequate.
625
626 control = dmarc_forensic_enable
627
628(AGAIN: You can choose not to send these forensic reports by simply
629not putting the dmarc_forensic_enable control line at any point in
630your exim config. If you don't tell it to send them, it will not
631send them.)
632
633There are no options to either control. Both must appear before
634the DATA acl.
635
636
6374. You can now run DMARC checks in incoming SMTP by using the
638"dmarc_status" ACL condition in the DATA ACL. You are required to
639call the spf condition first in the ACLs, then the "dmarc_status"
640condition. Putting this condition in the ACLs is required in order
641for a DMARC check to actually occur. All of the variables are set
642up before the DATA ACL, but there is no actual DMARC check that
643occurs until a "dmarc_status" condition is encountered in the ACLs.
644
645The dmarc_status condition takes a list of strings on its
646right-hand side. These strings describe recommended action based
647on the DMARC check. To understand what the policy recommendations
648mean, refer to the DMARC website above. Valid strings are:
649
650 o accept The DMARC check passed and the library recommends
651 accepting the email.
652 o reject The DMARC check failed and the library recommends
653 rejecting the email.
654 o quarantine The DMARC check failed and the library recommends
655 keeping it for further inspection.
7a8678e6 656 o none The DMARC check passed and the library recommends
657 no specific action, neutral.
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658 o norecord No policy section in the DMARC record for this
659 sender domain.
660 o nofrom Unable to determine the domain of the sender.
7a8678e6 661 o temperror Library error or dns error.
05070e30 662 o off The DMARC check was disabled for this email.
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663
664You can prefix each string with an exclamation mark to invert its
665meaning, for example "!accept" will match all results but
666"accept". The string list is evaluated left-to-right in a
667short-circuit fashion. When a string matches the outcome of the
668DMARC check, the condition succeeds. If none of the listed
669strings matches the outcome of the DMARC check, the condition
670fails.
671
672Of course, you can also use any other lookup method that Exim
673supports, including LDAP, Postgres, MySQL, etc, as long as the
8c8b8274 674result is a list of colon-separated strings.
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675
676Several expansion variables are set before the DATA ACL is
677processed, and you can use them in this ACL. The following
678expansion variables are available:
679
680 o $dmarc_status
681 This is a one word status indicating what the DMARC library
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682 thinks of the email. It is a combination of the results of
683 DMARC record lookup and the SPF/DKIM/DMARC processing results
684 (if a DMARC record was found). The actual policy declared
685 in the DMARC record is in a separate expansion variable.
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686
687 o $dmarc_status_text
688 This is a slightly longer, human readable status.
689
690 o $dmarc_used_domain
691 This is the domain which DMARC used to look up the DMARC
692 policy record.
693
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694 o $dmarc_domain_policy
695 This is the policy declared in the DMARC record. Valid values
696 are "none", "reject" and "quarantine". It is blank when there
697 is any error, including no DMARC record.
698
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699 o $dmarc_ar_header
700 This is the entire Authentication-Results header which you can
701 add using an add_header modifier.
702
703
7045. How to enable DMARC advanced operation:
705By default, Exim's DMARC configuration is intended to be
706non-intrusive and conservative. To facilitate this, Exim will not
707create any type of logging files without explicit configuration by
708you, the admin. Nor will Exim send out any emails/reports about
709DMARC issues without explicit configuration by you, the admin (other
710than typical bounce messages that may come about due to ACL
711processing or failure delivery issues).
712
713In order to log statistics suitable to be imported by the opendmarc
714tools, you need to:
715a. Configure the global setting dmarc_history_file.
716b. Configure cron jobs to call the appropriate opendmarc history
717 import scripts and truncating the dmarc_history_file.
718
719In order to send forensic reports, you need to:
720a. Configure the global setting dmarc_forensic_sender.
721b. Configure, somewhere before the DATA ACL, the control option to
722 enable sending DMARC forensic reports.
723
724
7256. Example usage:
726(RCPT ACL)
727 warn domains = +local_domains
728 hosts = +local_hosts
12d0043d 729 control = dmarc_disable_verify
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730
731 warn !domains = +screwed_up_dmarc_records
732 control = dmarc_enable_forensic
733
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734 warn condition = (lookup if destined to mailing list)
735 set acl_m_mailing_list = 1
736
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737(DATA ACL)
738 warn dmarc_status = accept : none : off
739 !authenticated = *
740 log_message = DMARC DEBUG: $dmarc_status $dmarc_used_domain
741 add_header = $dmarc_ar_header
742
743 warn dmarc_status = !accept
744 !authenticated = *
745 log_message = DMARC DEBUG: '$dmarc_status' for $dmarc_used_domain
746
747 warn dmarc_status = quarantine
748 !authenticated = *
749 set $acl_m_quarantine = 1
750 # Do something in a transport with this flag variable
751
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752 deny condition = ${if eq{$dmarc_domain_policy}{reject}}
753 condition = ${if eq{$acl_m_mailing_list}{1}}
754 message = Messages from $dmarc_used_domain break mailing lists
755
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756 deny dmarc_status = reject
757 !authenticated = *
758 message = Message from $domain_used_domain failed sender's DMARC policy, REJECT
759
760
761
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762Transport post-delivery actions
763--------------------------------------------------------------
764
765An arbitrary per-transport string can be expanded on successful delivery,
766and (for SMTP transports) a second string on deferrals caused by a host error.
767This feature may be used, for example, to write exim internal log information
768(not available otherwise) into a database.
769
770In order to use the feature, you must set
771
772EXPERIMENTAL_TPDA=yes
773
774in your Local/Makefile
775
776and define the expandable strings in the runtime config file, to
777be executed at end of delivery.
778
779Additionally, there are 6 more variables, available at end of
780delivery:
781
782tpda_delivery_ip IP of host, which has accepted delivery
783tpda_delivery_port Port of remote host which has accepted delivery
784tpda_delivery_fqdn FQDN of host, which has accepted delivery
785tpda_delivery_local_part local part of address being delivered
786tpda_delivery_domain domain part of address being delivered
787tpda_delivery_confirmation SMTP confirmation message
788
789In case of a deferral caused by a host-error:
790tpda_defer_errno Error number
791tpda_defer_errstr Error string possibly containing more details
792
793The $router_name and $transport_name variables are also usable.
794
795
796To take action after successful deliveries, set the following option
797on any transport of interest.
798
799tpda_delivery_action
800
801An example might look like:
802
803tpda_delivery_action = \
804${lookup pgsql {SELECT * FROM record_Delivery( \
805 '${quote_pgsql:$sender_address_domain}',\
806 '${quote_pgsql:${lc:$sender_address_local_part}}', \
807 '${quote_pgsql:$tpda_delivery_domain}', \
808 '${quote_pgsql:${lc:$tpda_delivery_local_part}}', \
809 '${quote_pgsql:$tpda_delivery_ip}', \
810 '${quote_pgsql:${lc:$tpda_delivery_fqdn}}', \
811 '${quote_pgsql:$message_exim_id}')}}
812
813The string is expanded after the delivery completes and any
814side-effects will happen. The result is then discarded.
815Note that for complex operations an ACL expansion can be used.
816
817
818In order to log host deferrals, add the following option to an SMTP
819transport:
820
821tpda_host_defer_action
822
823This is a private option of the SMTP transport. It is intended to
824log failures of remote hosts. It is executed only when exim has
825attempted to deliver a message to a remote host and failed due to
826an error which doesn't seem to be related to the individual
827message, sender, or recipient address.
7c261cc6 828See section 47.2 of the exim documentation for more details on how
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829this is determined.
830
831Example:
832
833tpda_host_defer_action = \
834${lookup mysql {insert into delivlog set \
835 msgid = '${quote_mysql:$message_exim_id}', \
836 senderlp = '${quote_mysql:${lc:$sender_address_local_part}}', \
837 senderdom = '${quote_mysql:$sender_address_domain}', \
838 delivlp = '${quote_mysql:${lc:$tpda_delivery_local_part}}', \
839 delivdom = '${quote_mysql:$tpda_delivery_domain}', \
840 delivip = '${quote_mysql:$tpda_delivery_ip}', \
841 delivport = '${quote_mysql:$tpda_delivery_port}', \
842 delivfqdn = '${quote_mysql:$tpda_delivery_fqdn}', \
843 deliverrno = '${quote_mysql:$tpda_defer_errno}', \
844 deliverrstr = '${quote_mysql:$tpda_defer_errstr}' \
845 }}
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847
848Redis Lookup
849--------------------------------------------------------------
850
851Redis is open source advanced key-value data store. This document
852does not explain the fundamentals, you should read and understand how
853it works by visiting the website at http://www.redis.io/.
854
855Redis lookup support is added via the hiredis library. Visit:
856
857 https://github.com/redis/hiredis
858
859to obtain a copy, or find it in your operating systems package repository.
860If building from source, this description assumes that headers will be in
861/usr/local/include, and that the libraries are in /usr/local/lib.
862
8631. In order to build exim with Redis lookup support add
864
865EXPERIMENTAL_REDIS=yes
866
867to your Local/Makefile. (Re-)build/install exim. exim -d should show
868Experimental_Redis in the line "Support for:".
869
870EXPERIMENTAL_REDIS=yes
871LDFLAGS += -lhiredis
872# CFLAGS += -I/usr/local/include
873# LDFLAGS += -L/usr/local/lib
874
875The first line sets the feature to include the correct code, and
876the second line says to link the hiredis libraries into the
877exim binary. The commented out lines should be uncommented if you
878built hiredis from source and installed in the default location.
879Adjust the paths if you installed them elsewhere, but you do not
880need to uncomment them if an rpm (or you) installed them in the
881package controlled locations (/usr/include and /usr/lib).
882
883
8842. Use the following global settings to configure Redis lookup support:
885
886Required:
887redis_servers This option provides a list of Redis servers
888 and associated connection data, to be used in
889 conjunction with redis lookups. The option is
890 only available if Exim is configured with Redis
891 support.
892
893For example:
894
895redis_servers = 127.0.0.1/10/ - using database 10 with no password
896redis_servers = 127.0.0.1//password - to make use of the default database of 0 with a password
897redis_servers = 127.0.0.1// - for default database of 0 with no password
898
8993. Once you have the Redis servers defined you can then make use of the
900experimental Redis lookup by specifying ${lookup redis{}} in a lookup query.
901
9024. Example usage:
903
904(Host List)
905hostlist relay_from_ips = <\n ${lookup redis{SMEMBERS relay_from_ips}}
906
907Where relay_from_ips is a Redis set which contains entries such as "192.168.0.0/24" "10.0.0.0/8" and so on.
908The result set is returned as
909192.168.0.0/24
91010.0.0.0/8
911..
912.
913
914(Domain list)
915domainlist virtual_domains = ${lookup redis {HGET $domain domain}}
916
917Where $domain is a hash which includes the key 'domain' and the value '$domain'.
918
919(Adding or updating an existing key)
920set acl_c_spammer = ${if eq{${lookup redis{SPAMMER_SET}}}{OK}}
921
922Where SPAMMER_SET is a macro and it is defined as
923
924"SET SPAMMER <some_value>"
925
926(Getting a value from Redis)
927
928set acl_c_spam_host = ${lookup redis{GET...}}
929
930
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931Proxy Protocol Support
932--------------------------------------------------------------
933
934Exim now has Experimental "Proxy Protocol" support. It was built on
935specifications from:
936http://haproxy.1wt.eu/download/1.5/doc/proxy-protocol.txt
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937Above URL revised May 2014 to change version 2 spec:
938http://git.1wt.eu/web?p=haproxy.git;a=commitdiff;h=afb768340c9d7e50d8e
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939
940The purpose of this function is so that an application load balancer,
941such as HAProxy, can sit in front of several Exim servers and Exim
942will log the IP that is connecting to the proxy server instead of
943the IP of the proxy server when it connects to Exim. It resets the
944$sender_address_host and $sender_address_port to the IP:port of the
945connection to the proxy. It also re-queries the DNS information for
946this new IP address so that the original sender's hostname and IP
947get logged in the Exim logfile. There is no logging if a host passes or
948fails Proxy Protocol negotiation, but it can easily be determined and
949recorded in an ACL (example is below).
950
9511. To compile Exim with Proxy Protocol support, put this in
952Local/Makefile:
953
954EXPERIMENTAL_PROXY=yes
955
9562. Global configuration settings:
957
958proxy_required_hosts = HOSTLIST
959
960The proxy_required_hosts option will require any IP in that hostlist
961to use Proxy Protocol. The specification of Proxy Protocol is very
962strict, and if proxy negotiation fails, Exim will not allow any SMTP
963command other than QUIT. (See end of this section for an example.)
964The option is expanded when used, so it can be a hostlist as well as
965string of IP addresses. Since it is expanded, specifying an alternate
966separator is supported for ease of use with IPv6 addresses.
967
968To log the IP of the proxy in the incoming logline, add:
969 log_selector = +proxy
970
971A default incoming logline (wrapped for appearance) will look like this:
972
973 2013-11-04 09:25:06 1VdNti-0001OY-1V <= me@example.net
974 H=mail.example.net [1.2.3.4] P=esmtp S=433
975
976With the log selector enabled, an email that was proxied through a
977Proxy Protocol server at 192.168.1.2 will look like this:
978
979 2013-11-04 09:25:06 1VdNti-0001OY-1V <= me@example.net
980 H=mail.example.net [1.2.3.4] P=esmtp PRX=192.168.1.2 S=433
981
9823. In the ACL's the following expansion variables are available.
983
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984proxy_host_address The (internal) src IP of the proxy server
985 making the connection to the Exim server.
986proxy_host_port The (internal) src port the proxy server is
987 using to connect to the Exim server.
988proxy_target_address The dest (public) IP of the remote host to
989 the proxy server.
990proxy_target_port The dest port the remote host is using to
991 connect to the proxy server.
992proxy_session Boolean, yes/no, the connected host is required
993 to use Proxy Protocol.
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994
995There is no expansion for a failed proxy session, however you can detect
996it by checking if $proxy_session is true but $proxy_host is empty. As
997an example, in my connect ACL, I have:
998
999 warn condition = ${if and{ {bool{$proxy_session}} \
a3bddaa8 1000 {eq{$proxy_host_address}{}} } }
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1001 log_message = Failed required proxy protocol negotiation \
1002 from $sender_host_name [$sender_host_address]
1003
1004 warn condition = ${if and{ {bool{$proxy_session}} \
a3bddaa8 1005 {!eq{$proxy_host_address}{}} } }
a3c86431 1006 # But don't log health probes from the proxy itself
a3bddaa8 1007 condition = ${if eq{$proxy_host_address}{$sender_host_address} \
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1008 {false}{true}}
1009 log_message = Successfully proxied from $sender_host_name \
1010 [$sender_host_address] through proxy protocol \
a3bddaa8 1011 host $proxy_host_address
a3c86431 1012
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1013 # Possibly more clear
1014 warn logwrite = Remote Source Address: $sender_host_address:$sender_host_port
1015 logwrite = Proxy Target Address: $proxy_target_address:$proxy_target_port
1016 logwrite = Proxy Internal Address: $proxy_host_address:$proxy_host_port
1017 logwrite = Internal Server Address: $received_ip_address:$received_port
1018
1019
2365d793 10204. Recommended ACL additions:
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1021 - Since the real connections are all coming from your proxy, and the
1022 per host connection tracking is done before Proxy Protocol is
1023 evaluated, smtp_accept_max_per_host must be set high enough to
1024 handle all of the parallel volume you expect per inbound proxy.
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1025 - With the smtp_accept_max_per_host set so high, you lose the ability
1026 to protect your server from massive numbers of inbound connections
1027 from one IP. In order to prevent your server from being DOS'd, you
1028 need to add a per connection ratelimit to your connect ACL. I
1029 suggest something like this:
1030
1031 # Set max number of connections per host
1032 LIMIT = 5
1033 # Or do some kind of IP lookup in a flat file or database
1034 # LIMIT = ${lookup{$sender_host_address}iplsearch{/etc/exim/proxy_limits}}
1035
1036 defer message = Too many connections from this IP right now
1037 ratelimit = LIMIT / 5s / per_conn / strict
1038
1039
10405. Runtime issues to be aware of:
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1041 - The proxy has 3 seconds (hard-coded in the source code) to send the
1042 required Proxy Protocol header after it connects. If it does not,
1043 the response to any commands will be:
1044 "503 Command refused, required Proxy negotiation failed"
1045 - If the incoming connection is configured in Exim to be a Proxy
1046 Protocol host, but the proxy is not sending the header, the banner
1047 does not get sent until the timeout occurs. If the sending host
1048 sent any input (before the banner), this causes a standard Exim
1049 synchronization error (i.e. trying to pipeline before PIPELINING
1050 was advertised).
1051 - This is not advised, but is mentioned for completeness if you have
1052 a specific internal configuration that you want this: If the Exim
1053 server only has an internal IP address and no other machines in your
1054 organization will connect to it to try to send email, you may
1055 simply set the hostlist to "*", however, this will prevent local
1056 mail programs from working because that would require mail from
1057 localhost to use Proxy Protocol. Again, not advised!
1058
2365d793 10596. Example of a refused connection because the Proxy Protocol header was
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1060not sent from a host configured to use Proxy Protocol. In the example,
1061the 3 second timeout occurred (when a Proxy Protocol banner should have
1062been sent), the banner was displayed to the user, but all commands are
1063rejected except for QUIT:
1064
1065# nc mail.example.net 25
1066220-mail.example.net, ESMTP Exim 4.82+proxy, Mon, 04 Nov 2013 10:45:59
1067220 -0800 RFC's enforced
1068EHLO localhost
1069503 Command refused, required Proxy negotiation failed
1070QUIT
1071221 mail.example.net closing connection
1072
1073
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1074DSN Support
1075--------------------------------------------------------------
1076
1077DSN Support tries to add RFC 3461 support to Exim. It adds support for
1078*) the additional parameters for MAIL FROM and RCPT TO
1079*) RFC complient MIME DSN messages for all of
1080 success, failure and delay notifications
1081*) dsn_advertise_hosts main option to select which hosts are able
1082 to use the extension
1083*) dsn_lasthop router switch to end DSN processing
1084
1085In case of failure reports this means that the last three parts, the message body
1086intro, size info and final text, of the defined template are ignored since there is no
1087logical place to put them in the MIME message.
1088
1089All the other changes are made without changing any defaults
1090
1091Building exim:
1092--------------
1093
1094Define
1095EXPERIMENTAL_DSN=YES
1096in your Local/Makefile.
1097
1098Configuration:
1099--------------
1100All DSNs are sent in MIME format if you built exim with EXPERIMENTAL_DSN=YES
1101No option needed to activate it, and no way to turn it off.
1102
1103Failure and delay DSNs are triggered as usual except a sender used NOTIFY=...
1104to prevent them.
1105
1106Support for Success DSNs is added and activated by NOTIFY=SUCCESS by clients.
1107
1108Add
1109dsn_advertise_hosts = *
1110or a more restrictive host_list to announce DSN in EHLO answers
1111
1112Those hosts can then use NOTIFY,ENVID,RET,ORCPT options.
1113
1114If a message is relayed to a DSN aware host without changing the envelope
1115recipient the options are passed along and no success DSN is generated.
1116
1117A redirect router will always trigger a success DSN if requested and the DSN
1118options are not passed any further.
1119
1120A success DSN always contains the recipient address as submitted by the
1121client as required by RFC. Rewritten addresses are never exposed.
1122
1123If you used DSN patch up to 1.3 before remove all "dsn_process" switches from
1124your routers since you don't need them anymore. There is no way to "gag"
1125success DSNs anymore. Announcing DSN means answering as requested.
1126
1127You can prevent Exim from passing DSN options along to other DSN aware hosts by defining
1128dsn_lasthop
1129in a router. Exim will then send the success DSN himself if requested as if
1130the next hop does not support DSN.
1131Adding it to a redirect router makes no difference.
9bdd29ad 1132
043b1248 1133
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1134Certificate name checking
1135--------------------------------------------------------------
1136The X509 certificates used for TLS are supposed be verified
1137that they are owned by the expected host. The coding of TLS
1138support to date has not made these checks.
1139
1140If built with EXPERIMENTAL_CERTNAMES defined, code is
1141included to do so, and a new smtp transport option
1142"tls_verify_cert_hostname" supported which takes a list of
1143names for which the checks must be made. The host must
1144also be in "tls_verify_hosts".
1145
1146Both Subject and Subject-Alternate-Name certificate fields
1147are supported, as are wildcard certificates (limited to
1148a single wildcard being the initial component of a 3-or-more
1149component FQDN).
1150
1151
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1152DANE
1153------------------------------------------------------------
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1154DNS-based Authentication of Named Entities, as applied
1155to SMTP over TLS, provides assurance to a client that
1156it is actually talking to the server it wants to rather
1157than some attacker operating a Man In The Middle (MITM)
1158operation. The latter can terminate the TLS connection
1159you make, and make another one to the server (so both
1160you and the server still think you have an encrypted
1161connection) and, if one of the "well known" set of
1162Certificate Authorities has been suborned - something
1163which *has* been seen already (2014), a verifiable
1164certificate (if you're using normal root CAs, eg. the
1165Mozilla set, as your trust anchors).
1166
1167What DANE does is replace the CAs with the DNS as the
1168trust anchor. The assurance is limited to a) the possibility
1169that the DNS has been suborned, b) mistakes made by the
1170admins of the target server. The attack surface presented
1171by (a) is thought to be smaller than that of the set
1172of root CAs.
1173
1174DANE scales better than having to maintain (and
1175side-channel communicate) copies of server certificates
1176for every possible target server. It also scales
1177(slightly) better than having to maintain on an SMTP
1178client a copy of the standard CAs bundle. It also
1179means not having to pay a CA for certificates.
1180
1181DANE requires a server operator to do three things:
11821) run DNSSEC. This provides assurance to clients
1183that DNS lookups they do for the server have not
1184been tampered with.
11852) add TLSA DNS records. These say what the server
1186certificate for a TLS connection should be.
11873) offer a server certificate, or certificate chain,
1188in TLS connections which is traceable to the one
1189defined by (one of?) the TSLA records
1190
1191There are no changes to Exim specific to server-side
1192operation of DANE.
1193
1194The TLSA record for the server may have "certificate
1195usage" of DANE_TA(2) or DANE_EE(3). The latter specifies
1196the End Entity directly, i.e. the certificate involved
1197is that of the server (and should be the sole one transmitted
1198during the TLS handshake); this is appropriate for a
1199single system, using a self-signed certificate.
1200 DANE_TA usage is effectively declaring a specific CA
1201to be used; this might be a private CA or a public,
1202well-known one. A private CA at simplest is just
1203a self-signed certificate which is used to sign
1204cerver certificates, but running one securely does
1205require careful arrangement. If a private CA is used
1206then either all clients must be primed with it, or
1207(probably simpler) the server TLS handshake must transmit
1208the entire certificate chain from CA to server-certificate.
1209If a public CA is used then all clients must be primed with it
1210(losing one advantage of DANE) - but the attack surface is
1211reduced from all public CAs to that single CA.
1212DANE_TA is commonly used for several services and/or
1213servers, each having a TLSA query-domain CNAME record,
1214all of which point to a single TLSA record.
1215
1216The TLSA record should have a Selector field of SPKI(1)
1217and a Matching Type fiels of SHA2-512(2).
1218
1219For use with the DANE_TA model, server certificates
1220must have a correct name (SubjectName or SubjectAltName).
1221
1222The use of OCSP-stapling should be considered, allowing
1223for fast revocation of certificates (which would otherwise
1224be limited by the DNS TTL on the TLSA records).
1225
1226
7a31d643
JH
1227For client-side DANE there are two new smtp transport options,
1228hosts_try_dane and hosts_require_dane. They do the obvious thing.
1229[ should they be domain-based rather than host-based? ]
7cac846b
JH
1230
1231DANE will only be usable if the target host has DNSSEC-secured
1232MX, A and TLSA records.
1233
1234(TODO: specify when fallback happens vs. when the host is not used)
1235
043b1248
JH
1236If dane is in use the following transport options are ignored:
1237 tls_verify_hosts
1238 tls_try_verify_hosts
1239 tls_verify_certificates
1240 tls_crl
1241 tls_verify_cert_hostnames
7cac846b 1242 hosts_require_ocsp (might rethink those two)
043b1248
JH
1243 hosts_request_ocsp
1244
7cac846b
JH
1245Currently dnssec_request_domains must be active (need to think about that)
1246and dnssec_require_domains is ignored.
043b1248 1247
e51c7be2 1248
ee161e8f
PH
1249--------------------------------------------------------------
1250End of file
1251--------------------------------------------------------------