| 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 |
| 5 | about experimental features, all of which are unstable and |
| 6 | liable to incompatible change. |
| 7 | |
| 8 | |
| 9 | Brightmail AntiSpam (BMI) support |
| 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 |
| 33 | 2) Set up main BMI options (top section of Exim config file) |
| 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 | |
| 40 | These four steps are explained in more details below. |
| 41 | |
| 42 | 1) Adding support for BMI at compile time |
| 43 | |
| 44 | To compile with BMI support, you need to link Exim against |
| 45 | the Brightmail 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 |
| 52 | CFLAGS=-I/path/to/the/dir/with/the/includefile |
| 53 | EXTRALIBS_EXIM=-L/path/to/the/dir/with/the/library -lbmiclient_single |
| 54 | |
| 55 | If you use other CFLAGS or EXTRALIBS_EXIM settings then |
| 56 | merge the content of these lines with them. |
| 57 | |
| 58 | Note for BMI6.x users: You'll also have to add -lxml2_single |
| 59 | to the EXTRALIBS_EXIM line. Users of 5.5x do not need to do |
| 60 | this. |
| 61 | |
| 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 | |
| 69 | 2) Setting up BMI support in the Exim main configuration |
| 70 | |
| 71 | To enable BMI support in the main Exim configuration, you |
| 72 | should set the path to the main BMI configuration file with |
| 73 | the "bmi_config_file" option, like this: |
| 74 | |
| 75 | bmi_config_file = /opt/brightmail/etc/brightmail.cfg |
| 76 | |
| 77 | This must go into section 1 of Exim's configuration file (You |
| 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. |
| 84 | |
| 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 |
| 96 | the "accept" blocks from Exim's default configuration file: |
| 97 | |
| 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 |
| 108 | |
| 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 |
| 119 | at that stage. From Exim's view, a verdict can have the |
| 120 | following outcomes: |
| 121 | |
| 122 | o deliver the message normally |
| 123 | o deliver the message to an alternate location |
| 124 | o do not deliver the message |
| 125 | |
| 126 | To query the verdict for a recipient, the implementation |
| 127 | offers the following tools: |
| 128 | |
| 129 | |
| 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: |
| 134 | |
| 135 | o bmi_deliver_default |
| 136 | |
| 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. |
| 141 | |
| 142 | o bmi_deliver_alternate |
| 143 | |
| 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. |
| 150 | |
| 151 | o bmi_dont_deliver |
| 152 | |
| 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: |
| 157 | |
| 158 | # don't deliver messages handled by the BMI server |
| 159 | bmi_blackhole: |
| 160 | driver = redirect |
| 161 | bmi_dont_deliver |
| 162 | data = :blackhole: |
| 163 | |
| 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. |
| 168 | |
| 169 | |
| 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: |
| 175 | |
| 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 |
| 181 | |
| 182 | |
| 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: |
| 187 | |
| 188 | o $bmi_base64_verdict |
| 189 | |
| 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: |
| 193 | |
| 194 | localuser: |
| 195 | driver = accept |
| 196 | check_local_user |
| 197 | headers_add = X-Brightmail-Verdict: $bmi_base64_verdict |
| 198 | transport = local_delivery |
| 199 | |
| 200 | If there is no verdict available for the recipient being |
| 201 | routed, this variable contains the empty string. |
| 202 | |
| 203 | o $bmi_base64_tracker_verdict |
| 204 | |
| 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: |
| 209 | |
| 210 | localuser: |
| 211 | driver = accept |
| 212 | check_local_user |
| 213 | headers_add = X-Brightmail-Tracker: $bmi_base64_tracker_verdict |
| 214 | transport = local_delivery |
| 215 | |
| 216 | If there is no verdict available for the recipient being |
| 217 | routed, this variable contains the empty string. |
| 218 | |
| 219 | o $bmi_alt_location |
| 220 | |
| 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. |
| 229 | |
| 230 | o $bmi_deliver |
| 231 | |
| 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. |
| 235 | |
| 236 | $bmi_deliver is '0': the message should NOT be delivered. |
| 237 | $bmi_deliver is '1': the message should be delivered. |
| 238 | |
| 239 | |
| 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. |
| 248 | |
| 249 | |
| 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 |
| 257 | already look up recipient data in Exim anyway (which can |
| 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'. |
| 269 | |
| 270 | The file format: |
| 271 | |
| 272 | user1@mydomain.com: <OPTIN STRING1>:<OPTIN STRING2> |
| 273 | user2@thatdomain.com: <OPTIN STRING3> |
| 274 | |
| 275 | |
| 276 | The example: |
| 277 | |
| 278 | accept domains = +relay_to_domains |
| 279 | endpass |
| 280 | verify = recipient |
| 281 | bmi_optin = ${lookup{$local_part@$domain}lsearch{/etc/exim/bmi_optin_data}} |
| 282 | control = bmi_run |
| 283 | |
| 284 | Of course, you can also use any other lookup method that |
| 285 | Exim supports, including LDAP, Postgres, MySQL, Oracle etc., |
| 286 | as long as the result is a list of colon-separated opt-in |
| 287 | strings. |
| 288 | |
| 289 | For a list of available opt-in strings, please contact your |
| 290 | Brightmail representative. |
| 291 | |
| 292 | |
| 293 | |
| 294 | |
| 295 | SRS (Sender Rewriting Scheme) Support (using libsrs_alt) |
| 296 | -------------------------------------------------------------- |
| 297 | See also below, for an alternative native support implementation. |
| 298 | |
| 299 | Exim currently includes SRS support via Miles Wilton's |
| 300 | libsrs_alt library. The current version of the supported |
| 301 | library is 0.5, there are reports of 1.0 working. |
| 302 | |
| 303 | In order to use SRS, you must get a copy of libsrs_alt from |
| 304 | |
| 305 | https://opsec.eu/src/srs/ |
| 306 | |
| 307 | (not the original source, which has disappeared.) |
| 308 | |
| 309 | Unpack the tarball, then refer to MTAs/README.EXIM |
| 310 | to proceed. You need to set |
| 311 | |
| 312 | EXPERIMENTAL_SRS=yes |
| 313 | |
| 314 | in your Local/Makefile. |
| 315 | |
| 316 | The following main-section options become available: |
| 317 | srs_config string |
| 318 | srs_hashlength int |
| 319 | srs_hashmin int |
| 320 | srs_maxage int |
| 321 | srs_secrets string |
| 322 | srs_usehash bool |
| 323 | srs_usetimestamp bool |
| 324 | |
| 325 | The redirect router gains these options (all of type string, unset by default): |
| 326 | srs |
| 327 | srs_alias |
| 328 | srs_condition |
| 329 | srs_dbinsert |
| 330 | srs_dbselect |
| 331 | |
| 332 | The following variables become available: |
| 333 | $srs_db_address |
| 334 | $srs_db_key |
| 335 | $srs_orig_recipient |
| 336 | $srs_orig_sender |
| 337 | $srs_recipient |
| 338 | $srs_status |
| 339 | |
| 340 | The predefined feature-macro _HAVE_SRS will be present. |
| 341 | Additional delivery log line elements, tagged with "SRS=" will show the srs sender. |
| 342 | For configuration information see https://github.com/Exim/exim/wiki/SRS . |
| 343 | |
| 344 | |
| 345 | |
| 346 | |
| 347 | SRS (Sender Rewriting Scheme) Support (native) |
| 348 | -------------------------------------------------------------- |
| 349 | This is less full-featured than the libsrs_alt version above. |
| 350 | |
| 351 | The Exim build needs to be done with this in Local/Makefile: |
| 352 | EXPERIMENTAL_SRS_NATIVE=yes |
| 353 | |
| 354 | The following are provided: |
| 355 | - an expansion item "srs_encode" |
| 356 | This takes three arguments: |
| 357 | - a site SRS secret |
| 358 | - the return_path |
| 359 | - the pre-forwarding domain |
| 360 | |
| 361 | - an expansion condition "inbound_srs" |
| 362 | This takes two arguments: the local_part to check, and a site SRS secret. |
| 363 | If the secret is zero-length, only the pattern of the local_part is checked. |
| 364 | The $srs_recipient variable is set as a side-effect. |
| 365 | |
| 366 | - an expansion variable $srs_recipient |
| 367 | This gets the original return_path encoded in the SRS'd local_part |
| 368 | |
| 369 | - predefined macros _HAVE_SRS and _HAVE_NATIVE_SRS |
| 370 | |
| 371 | Sample usage: |
| 372 | |
| 373 | #macro |
| 374 | SRS_SECRET = <pick something unique for your site for this> |
| 375 | |
| 376 | #routers |
| 377 | |
| 378 | outbound: |
| 379 | driver = dnslookup |
| 380 | # if outbound, and forwarding has been done, use an alternate transport |
| 381 | domains = ! +my_domains |
| 382 | transport = ${if eq {$local_part@$domain} \ |
| 383 | {$original_local_part@$original_domain} \ |
| 384 | {remote_smtp} {remote_forwarded_smtp}} |
| 385 | |
| 386 | inbound_srs: |
| 387 | driver = redirect |
| 388 | senders = : |
| 389 | domains = +my_domains |
| 390 | # detect inbound bounces which are SRS'd, and decode them |
| 391 | condition = ${if inbound_srs {$local_part} {SRS_SECRET}} |
| 392 | data = $srs_recipient |
| 393 | |
| 394 | inbound_srs_failure: |
| 395 | driver = redirect |
| 396 | senders = : |
| 397 | domains = +my_domains |
| 398 | # detect inbound bounces which look SRS'd but are invalid |
| 399 | condition = ${if inbound_srs {$local_part} {}} |
| 400 | allow_fail |
| 401 | data = :fail: Invalid SRS recipient address |
| 402 | |
| 403 | #... further routers here |
| 404 | |
| 405 | |
| 406 | # transport; should look like the non-forward outbound |
| 407 | # one, plus the max_rcpt and return_path options |
| 408 | remote_forwarded_smtp: |
| 409 | driver = smtp |
| 410 | # modify the envelope from, for mails that we forward |
| 411 | max_rcpt = 1 |
| 412 | return_path = ${srs_encode {SRS_SECRET} {$return_path} {$original_domain}} |
| 413 | |
| 414 | |
| 415 | |
| 416 | |
| 417 | DCC Support |
| 418 | -------------------------------------------------------------- |
| 419 | Distributed Checksum Clearinghouse; http://www.rhyolite.com/dcc/ |
| 420 | |
| 421 | *) Building exim |
| 422 | |
| 423 | In order to build exim with DCC support add |
| 424 | |
| 425 | EXPERIMENTAL_DCC=yes |
| 426 | |
| 427 | to your Makefile. (Re-)build/install exim. exim -d should show |
| 428 | EXPERIMENTAL_DCC under "Support for". |
| 429 | |
| 430 | |
| 431 | *) Configuration |
| 432 | |
| 433 | In the main section of exim.cf add at least |
| 434 | dccifd_address = /usr/local/dcc/var/dccifd |
| 435 | or |
| 436 | dccifd_address = <ip> <port> |
| 437 | |
| 438 | In the DATA ACL you can use the new condition |
| 439 | dcc = * |
| 440 | |
| 441 | After that "$dcc_header" contains the X-DCC-Header. |
| 442 | |
| 443 | Return values are: |
| 444 | fail for overall "R", "G" from dccifd |
| 445 | defer for overall "T" from dccifd |
| 446 | accept for overall "A", "S" from dccifd |
| 447 | |
| 448 | dcc = */defer_ok works as for spamd. |
| 449 | |
| 450 | The "$dcc_result" variable contains the overall result from DCC |
| 451 | answer. There will an X-DCC: header added to the mail. |
| 452 | |
| 453 | Usually you'll use |
| 454 | defer !dcc = * |
| 455 | to greylist with DCC. |
| 456 | |
| 457 | If you set, in the main section, |
| 458 | dcc_direct_add_header = true |
| 459 | then the dcc header will be added "in deep" and if the spool |
| 460 | file was already written it gets removed. This forces Exim to |
| 461 | write it again if needed. This helps to get the DCC Header |
| 462 | through to eg. SpamAssassin. |
| 463 | |
| 464 | If you want to pass even more headers in the middle of the |
| 465 | DATA stage you can set |
| 466 | $acl_m_dcc_add_header |
| 467 | to tell the DCC routines to add more information; eg, you might set |
| 468 | this to some results from ClamAV. Be careful. Header syntax is |
| 469 | not checked and is added "as is". |
| 470 | |
| 471 | In case you've troubles with sites sending the same queue items from several |
| 472 | hosts and fail to get through greylisting you can use |
| 473 | $acl_m_dcc_override_client_ip |
| 474 | |
| 475 | Setting $acl_m_dcc_override_client_ip to an IP address overrides the default |
| 476 | of $sender_host_address. eg. use the following ACL in DATA stage: |
| 477 | |
| 478 | warn set acl_m_dcc_override_client_ip = \ |
| 479 | ${lookup{$sender_helo_name}nwildlsearch{/etc/mail/multipleip_sites}{$value}{}} |
| 480 | condition = ${if def:acl_m_dcc_override_client_ip} |
| 481 | log_message = dbg: acl_m_dcc_override_client_ip set to \ |
| 482 | $acl_m_dcc_override_client_ip |
| 483 | |
| 484 | Then set something like |
| 485 | # cat /etc/mail/multipleip_sites |
| 486 | mout-xforward.gmx.net 82.165.159.12 |
| 487 | mout.gmx.net 212.227.15.16 |
| 488 | |
| 489 | Use a reasonable IP. eg. one the sending cluster actually uses. |
| 490 | |
| 491 | |
| 492 | |
| 493 | DSN extra information |
| 494 | --------------------- |
| 495 | If compiled with EXPERIMENTAL_DSN_INFO extra information will be added |
| 496 | to DSN fail messages ("bounces"), when available. The intent is to aid |
| 497 | tracing of specific failing messages, when presented with a "bounce" |
| 498 | complaint and needing to search logs. |
| 499 | |
| 500 | |
| 501 | The remote MTA IP address, with port number if nonstandard. |
| 502 | Example: |
| 503 | Remote-MTA: X-ip; [127.0.0.1]:587 |
| 504 | Rationale: |
| 505 | Several addresses may correspond to the (already available) |
| 506 | dns name for the remote MTA. |
| 507 | |
| 508 | The remote MTA connect-time greeting. |
| 509 | Example: |
| 510 | X-Remote-MTA-smtp-greeting: X-str; 220 the.local.host.name ESMTP Exim x.yz Tue, 2 Mar 1999 09:44:33 +0000 |
| 511 | Rationale: |
| 512 | This string sometimes presents the remote MTA's idea of its |
| 513 | own name, and sometimes identifies the MTA software. |
| 514 | |
| 515 | The remote MTA response to HELO or EHLO. |
| 516 | Example: |
| 517 | X-Remote-MTA-helo-response: X-str; 250-the.local.host.name Hello localhost [127.0.0.1] |
| 518 | Limitations: |
| 519 | Only the first line of a multiline response is recorded. |
| 520 | Rationale: |
| 521 | This string sometimes presents the remote MTA's view of |
| 522 | the peer IP connecting to it. |
| 523 | |
| 524 | The reporting MTA detailed diagnostic. |
| 525 | Example: |
| 526 | X-Exim-Diagnostic: X-str; SMTP error from remote mail server after RCPT TO:<d3@myhost.test.ex>: 550 hard error |
| 527 | Rationale: |
| 528 | This string sometimes give extra information over the |
| 529 | existing (already available) Diagnostic-Code field. |
| 530 | |
| 531 | |
| 532 | Note that non-RFC-documented field names and data types are used. |
| 533 | |
| 534 | |
| 535 | LMDB Lookup support |
| 536 | ------------------- |
| 537 | LMDB is an ultra-fast, ultra-compact, crash-proof key-value embedded data store. |
| 538 | It is modeled loosely on the BerkeleyDB API. You should read about the feature |
| 539 | set as well as operation modes at https://symas.com/products/lightning-memory-mapped-database/ |
| 540 | |
| 541 | LMDB single key lookup support is provided by linking to the LMDB C library. |
| 542 | The current implementation does not support writing to the LMDB database. |
| 543 | |
| 544 | Visit https://github.com/LMDB/lmdb to download the library or find it in your |
| 545 | operating systems package repository. |
| 546 | |
| 547 | If building from source, this description assumes that headers will be in |
| 548 | /usr/local/include, and that the libraries are in /usr/local/lib. |
| 549 | |
| 550 | 1. In order to build exim with LMDB lookup support add or uncomment |
| 551 | |
| 552 | EXPERIMENTAL_LMDB=yes |
| 553 | |
| 554 | to your Local/Makefile. (Re-)build/install exim. exim -d should show |
| 555 | Experimental_LMDB in the line "Support for:". |
| 556 | |
| 557 | EXPERIMENTAL_LMDB=yes |
| 558 | LDFLAGS += -llmdb |
| 559 | # CFLAGS += -I/usr/local/include |
| 560 | # LDFLAGS += -L/usr/local/lib |
| 561 | |
| 562 | The first line sets the feature to include the correct code, and |
| 563 | the second line says to link the LMDB libraries into the |
| 564 | exim binary. The commented out lines should be uncommented if you |
| 565 | built LMDB from source and installed in the default location. |
| 566 | Adjust the paths if you installed them elsewhere, but you do not |
| 567 | need to uncomment them if an rpm (or you) installed them in the |
| 568 | package controlled locations (/usr/include and /usr/lib). |
| 569 | |
| 570 | 2. Create your LMDB files, you can use the mdb_load utility which is |
| 571 | part of the LMDB distribution our your favourite language bindings. |
| 572 | |
| 573 | 3. Add the single key lookups to your exim.conf file, example lookups |
| 574 | are below. |
| 575 | |
| 576 | ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}} |
| 577 | ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}{$value}fail} |
| 578 | ${lookup{$sender_address_domain}lmdb{/var/lib/baruwa/data/db/relaydomains.mdb}} |
| 579 | |
| 580 | |
| 581 | Queuefile transport |
| 582 | ------------------- |
| 583 | Queuefile is a pseudo transport which does not perform final delivery. |
| 584 | It simply copies the exim spool files out of the spool directory into |
| 585 | an external directory retaining the exim spool format. |
| 586 | |
| 587 | The spool files can then be processed by external processes and then |
| 588 | requeued into exim spool directories for final delivery. |
| 589 | However, note carefully the warnings in the main documentation on |
| 590 | qpool file formats. |
| 591 | |
| 592 | The motivation/inspiration for the transport is to allow external |
| 593 | processes to access email queued by exim and have access to all the |
| 594 | information which would not be available if the messages were delivered |
| 595 | to the process in the standard email formats. |
| 596 | |
| 597 | The mailscanner package is one of the processes that can take advantage |
| 598 | of this transport to filter email. |
| 599 | |
| 600 | The transport can be used in the same way as the other existing transports, |
| 601 | i.e by configuring a router to route mail to a transport configured with |
| 602 | the queuefile driver. |
| 603 | |
| 604 | The transport only takes one option: |
| 605 | |
| 606 | * directory - This is used to specify the directory messages should be |
| 607 | copied to. Expanded. |
| 608 | |
| 609 | The generic transport options (body_only, current_directory, disable_logging, |
| 610 | debug_print, delivery_date_add, envelope_to_add, event_action, group, |
| 611 | headers_add, headers_only, headers_remove, headers_rewrite, home_directory, |
| 612 | initgroups, max_parallel, message_size_limit, rcpt_include_affixes, |
| 613 | retry_use_local_part, return_path, return_path_add, shadow_condition, |
| 614 | shadow_transport, transport_filter, transport_filter_timeout, user) are |
| 615 | ignored. |
| 616 | |
| 617 | Sample configuration: |
| 618 | |
| 619 | (Router) |
| 620 | |
| 621 | scan: |
| 622 | driver = accept |
| 623 | transport = scan |
| 624 | |
| 625 | (Transport) |
| 626 | |
| 627 | scan: |
| 628 | driver = queuefile |
| 629 | directory = /var/spool/baruwa-scanner/input |
| 630 | |
| 631 | |
| 632 | In order to build exim with Queuefile transport support add or uncomment |
| 633 | |
| 634 | EXPERIMENTAL_QUEUEFILE=yes |
| 635 | |
| 636 | to your Local/Makefile. (Re-)build/install exim. exim -d should show |
| 637 | Experimental_QUEUEFILE in the line "Support for:". |
| 638 | |
| 639 | |
| 640 | ARC support |
| 641 | ----------- |
| 642 | Specification: https://tools.ietf.org/html/draft-ietf-dmarc-arc-protocol-11 |
| 643 | Note that this is not an RFC yet, so may change. |
| 644 | |
| 645 | [RFC 8617 was published 2019/06. Draft 11 was 2018/01. A review of the |
| 646 | changes has not yet been done] |
| 647 | |
| 648 | ARC is intended to support the utility of SPF and DKIM in the presence of |
| 649 | intermediaries in the transmission path - forwarders and mailinglists - |
| 650 | by establishing a cryptographically-signed chain in headers. |
| 651 | |
| 652 | Normally one would only bother doing ARC-signing when functioning as |
| 653 | an intermediary. One might do verify for local destinations. |
| 654 | |
| 655 | ARC uses the notion of a "ADministrative Management Domain" (ADMD). |
| 656 | Described in RFC 5598 (section 2.3), this is essentially a set of |
| 657 | mail-handling systems that mail transits that are all under the control |
| 658 | of one organisation. A label should be chosen to identify the ADMD. |
| 659 | Messages should be ARC-verified on entry to the ADMD, and ARC-signed on exit |
| 660 | from it. |
| 661 | |
| 662 | |
| 663 | Building with ARC Support |
| 664 | -- |
| 665 | Enable using EXPERIMENTAL_ARC=yes in your Local/Makefile. |
| 666 | You must also have DKIM present (not disabled), and you very likely |
| 667 | want to have SPF enabled. |
| 668 | |
| 669 | |
| 670 | Verification |
| 671 | -- |
| 672 | An ACL condition is provided to perform the "verifier actions" detailed |
| 673 | in section 6 of the above specification. It may be called from the DATA ACL |
| 674 | and succeeds if the result matches any of a given list. |
| 675 | It also records the highest ARC instance number (the chain size) |
| 676 | and verification result for later use in creating an Authentication-Results: |
| 677 | standard header. |
| 678 | |
| 679 | verify = arc/<acceptable_list> none:fail:pass |
| 680 | |
| 681 | add_header = :at_start:${authresults {<admd-identifier>}} |
| 682 | |
| 683 | Note that it would be wise to strip incoming messages of A-R headers |
| 684 | that claim to be from our own <admd-identifier>. |
| 685 | |
| 686 | There are four new variables: |
| 687 | |
| 688 | $arc_state One of pass, fail, none |
| 689 | $arc_state_reason (if fail, why) |
| 690 | $arc_domains colon-sep list of ARC chain domains, in chain order. |
| 691 | problematic elements may have empty list elements |
| 692 | $arc_oldest_pass lowest passing instance number of chain |
| 693 | |
| 694 | Example: |
| 695 | logwrite = oldest-p-ams: <${reduce {$lh_ARC-Authentication-Results:} \ |
| 696 | {} \ |
| 697 | {${if = {$arc_oldest_pass} \ |
| 698 | {${extract {i}{${extract {1}{;}{$item}}}}} \ |
| 699 | {$item} {$value}}} \ |
| 700 | }> |
| 701 | |
| 702 | Receive log lines for an ARC pass will be tagged "ARC". |
| 703 | |
| 704 | |
| 705 | Signing |
| 706 | -- |
| 707 | arc_sign = <admd-identifier> : <selector> : <privkey> [ : <options> ] |
| 708 | An option on the smtp transport, which constructs and prepends to the message |
| 709 | an ARC set of headers. The textually-first Authentication-Results: header |
| 710 | is used as a basis (you must have added one on entry to the ADMD). |
| 711 | Expanded as a whole; if unset, empty or forced-failure then no signing is done. |
| 712 | If it is set, all of the first three elements must be non-empty. |
| 713 | |
| 714 | The fourth element is optional, and if present consists of a comma-separated list |
| 715 | of options. The options implemented are |
| 716 | |
| 717 | timestamps Add a t= tag to the generated AMS and AS headers, with the |
| 718 | current time. |
| 719 | expire[=<val>] Add an x= tag to the generated AMS header, with an expiry time. |
| 720 | If the value <val> is an plain number it is used unchanged. |
| 721 | If it starts with a '+' then the following number is added |
| 722 | to the current time, as an offset in seconds. |
| 723 | If a value is not given it defaults to a one month offset. |
| 724 | |
| 725 | [As of writing, gmail insist that a t= tag on the AS is mandatory] |
| 726 | |
| 727 | Caveats: |
| 728 | * There must be an Authentication-Results header, presumably added by an ACL |
| 729 | while receiving the message, for the same ADMD, for arc_sign to succeed. |
| 730 | This requires careful coordination between inbound and outbound logic. |
| 731 | |
| 732 | Only one A-R header is taken account of. This is a limitation versus |
| 733 | the ARC spec (which says that all A-R headers from within the ADMD must |
| 734 | be used). |
| 735 | |
| 736 | * If passing a message to another system, such as a mailing-list manager |
| 737 | (MLM), between receipt and sending, be wary of manipulations to headers made |
| 738 | by the MLM. |
| 739 | + For instance, Mailman with REMOVE_DKIM_HEADERS==3 might improve |
| 740 | deliverability in a pre-ARC world, but that option also renames the |
| 741 | Authentication-Results header, which breaks signing. |
| 742 | |
| 743 | * Even if you use multiple DKIM keys for different domains, the ARC concept |
| 744 | should try to stick to one ADMD, so pick a primary domain and use that for |
| 745 | AR headers and outbound signing. |
| 746 | |
| 747 | Signing is not compatible with cutthrough delivery; any (before expansion) |
| 748 | value set for the option will result in cutthrough delivery not being |
| 749 | used via the transport in question. |
| 750 | |
| 751 | |
| 752 | |
| 753 | |
| 754 | TLS Session Resumption |
| 755 | ---------------------- |
| 756 | TLS Session Resumption for TLS 1.2 and TLS 1.3 connections can be used (defined |
| 757 | in RFC 5077 for 1.2). The support for this can be included by building with |
| 758 | EXPERIMENTAL_TLS_RESUME defined. This requires GnuTLS 3.6.3 or OpenSSL 1.1.1 |
| 759 | (or later). |
| 760 | |
| 761 | Session resumption (this is the "stateless" variant) involves the server sending |
| 762 | a "session ticket" to the client on one connection, which can be stored by the |
| 763 | client and used for a later session. The ticket contains sufficient state for |
| 764 | the server to reconstruct the TLS session, avoiding some expensive crypto |
| 765 | calculation and one full packet roundtrip time. |
| 766 | |
| 767 | Operational cost/benefit: |
| 768 | The extra data being transmitted costs a minor amount, and the client has |
| 769 | extra costs in storing and retrieving the data. |
| 770 | |
| 771 | In the Exim/Gnutls implementation the extra cost on an initial connection |
| 772 | which is TLS1.2 over a loopback path is about 6ms on 2017-laptop class hardware. |
| 773 | The saved cost on a subsequent connection is about 4ms; three or more |
| 774 | connections become a net win. On longer network paths, two or more |
| 775 | connections will have an average lower startup time thanks to the one |
| 776 | saved packet roundtrip. TLS1.3 will save the crypto cpu costs but not any |
| 777 | packet roundtrips. |
| 778 | |
| 779 | Since a new hints DB is used, the hints DB maintenance should be updated |
| 780 | to additionally handle "tls". |
| 781 | |
| 782 | Security aspects: |
| 783 | The session ticket is encrypted, but is obviously an additional security |
| 784 | vulnarability surface. An attacker able to decrypt it would have access |
| 785 | all connections using the resumed session. |
| 786 | The session ticket encryption key is not committed to storage by the server |
| 787 | and is rotated regularly (OpenSSL: 1hr, and one previous key is used for |
| 788 | overlap; GnuTLS 6hr but does not specify any overlap). |
| 789 | Tickets have limited lifetime (2hr, and new ones issued after 1hr under |
| 790 | OpenSSL. GnuTLS 2hr, appears to not do overlap). |
| 791 | |
| 792 | There is a question-mark over the security of the Diffie-Helman parameters |
| 793 | used for session negotiation. TBD. q-value; cf bug 1895 |
| 794 | |
| 795 | Observability: |
| 796 | New log_selector "tls_resumption", appends an asterisk to the tls_cipher "X=" |
| 797 | element. |
| 798 | |
| 799 | Variables $tls_{in,out}_resumption have bits 0-4 indicating respectively |
| 800 | support built, client requested ticket, client offered session, |
| 801 | server issued ticket, resume used. A suitable decode list is provided |
| 802 | in the builtin macro _RESUME_DECODE for ${listextract {}{}}. |
| 803 | |
| 804 | Issues: |
| 805 | In a resumed session: |
| 806 | $tls_{in,out}_cipher will have values different to the original (under GnuTLS) |
| 807 | $tls_{in,out}_ocsp will be "not requested" or "no response", and |
| 808 | hosts_require_ocsp will fail |
| 809 | |
| 810 | |
| 811 | |
| 812 | Dovecot authenticator via inet socket |
| 813 | ------------------------------------ |
| 814 | If Dovecot is configured similar to :- |
| 815 | |
| 816 | service auth { |
| 817 | ... |
| 818 | #SASL |
| 819 | inet_listener { |
| 820 | name = exim |
| 821 | port = 12345 |
| 822 | } |
| 823 | ... |
| 824 | } |
| 825 | |
| 826 | then an Exim authenticator can be configured :- |
| 827 | |
| 828 | dovecot-plain: |
| 829 | driver = dovecot |
| 830 | public_name = PLAIN |
| 831 | server_socket = dovecot_server_name 12345 |
| 832 | server_tls = true |
| 833 | server_set_id = $auth1 |
| 834 | |
| 835 | If the server_socket does not start with a / it is taken as a hostname (or IP); |
| 836 | and a whitespace-separated port number must be given. |
| 837 | |
| 838 | |
| 839 | |
| 840 | -------------------------------------------------------------- |
| 841 | End of file |
| 842 | -------------------------------------------------------------- |