diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/doc-docbook/spec.xfpt | 249 | ||||
| -rw-r--r-- | doc/doc-txt/ChangeLog | 2 | ||||
| -rw-r--r-- | doc/doc-txt/OptionLists.txt | 6 | ||||
| -rw-r--r-- | doc/doc-txt/experimental-spec.txt | 233 |
4 files changed, 251 insertions, 239 deletions
diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt index 00ff91d85..c2adc9ea6 100644 --- a/doc/doc-docbook/spec.xfpt +++ b/doc/doc-docbook/spec.xfpt @@ -12079,6 +12079,15 @@ contain the trailing slash. If &$config_file$& does not contain a slash, .vindex "&$config_file$&" The name of the main configuration file Exim is using. +.new +.vitem &$dmarc_domain_policy$& &&& + &$dmarc_status$& &&& + &$dmarc_status_text$& &&& + &$dmarc_used_domains$& +Results of DMARC verification. +For details see section &<<SECDMARC>>&. +.wen + .vitem &$dkim_verify_status$& Results of DKIM verification. For details see section &<<SECDKIMVFY>>&. @@ -39752,11 +39761,11 @@ There is no dot-stuffing (and no dot-termination). . //////////////////////////////////////////////////////////////////////////// . //////////////////////////////////////////////////////////////////////////// -.chapter "DKIM and SPF" "CHAPdkim" &&& - "DKIM and SPF Support" -.cindex "DKIM" +.chapter "DKIM, SPF and DMARC" "CHAPdkim" &&& + "DKIM, SPF and DMARC Support" .section "DKIM (DomainKeys Identified Mail)" SECDKIM +.cindex "DKIM" DKIM is a mechanism by which messages sent by some entity can be provably linked to a domain which that entity controls. It permits reputation to @@ -40446,6 +40455,240 @@ The lookup will return the same result strings as can appear in + +.new +.section DMARC SECDMARC +.cindex DMARC verification + +DMARC combines feedback from SPF, DKIM, and header From: in order +to attempt to provide better indicators of the authenticity of an +email. This document does not explain the fundamentals; you +should read and understand how it works by visiting the website at +&url(http://www.dmarc.org/). + +If Exim is built with DMARC support, +the libopendmarc library is used. + +For building Exim yourself, obtain the library from +&url(http://sourceforge.net/projects/opendmarc/) +to obtain a copy, or find it in your favorite rpm package +repository. You will need to attend to the local/Makefile feature +SUPPORT_DMARC and the associated LDFLAGS addition. +This description assumes +that headers will be in /usr/local/include, and that the libraries +are in /usr/local/lib. + +. subsection + +There are three main-configuration options: +.cindex DMARC "configuration options" + +The &%dmarc_tld_file%& option +.oindex &%dmarc_tld_file%& +defines the location of a text file of valid +top level domains the opendmarc library uses +during domain parsing. Maintained by Mozilla, +the most current version can be downloaded +from a link at &url(http://publicsuffix.org/list/). +See also util/renew-opendmarc-tlds.sh script. +The default for the option is currently +/etc/exim/opendmarc.tlds + +The &%dmarc_history_file%& option, if set +.oindex &%dmarc_history_file%& +defines the location of a file to log results +of dmarc verification on inbound emails. The +contents are importable by the opendmarc tools +which will manage the data, send out DMARC +reports, and expire the data. Make sure the +directory of this file is writable by the user +exim runs as. +The default is unset. + +The &%dmarc_forensic_sender%& option +.oindex &%dmarc_forensic_sender%& +defines an alternate email address to use when sending a +forensic report detailing alignment failures +if a sender domain's dmarc record specifies it +and you have configured Exim to send them. +If set, this is expanded and used for the +From: header line; the address is extracted +from it and used for the envelope from. +If not set (the default), the From: header is expanded from +the dsn_from option, and <> is used for the +envelope from. + +. I wish we had subsections... + +.cindex DMARC controls +By default, the DMARC processing will run for any remote, +non-authenticated user. It makes sense to only verify DMARC +status of messages coming from remote, untrusted sources. You can +use standard conditions such as hosts, senders, etc, to decide that +DMARC verification should *not* be performed for them and disable +DMARC with a control setting: +.code + control = dmarc_disable_verify +.endd +A DMARC record can also specify a "forensic address", which gives +exim an email address to submit reports about failed alignment. +Exim does not do this by default because in certain conditions it +results in unintended information leakage (what lists a user might +be subscribed to, etc). You must configure exim to submit forensic +reports to the owner of the domain. If the DMARC record contains a +forensic address and you specify the control statement below, then +exim will send these forensic emails. It's also advised that you +configure a dmarc_forensic_sender because the default sender address +construction might be inadequate. +.code + control = dmarc_enable_forensic +.endd +(AGAIN: You can choose not to send these forensic reports by simply +not putting the dmarc_enable_forensic control line at any point in +your exim config. If you don't tell it to send them, it will not +send them.) + +There are no options to either control. Both must appear before +the DATA acl. + +. subsection + +DMARC checks cam be run on incoming SMTP messages by using the +"dmarc_status" ACL condition in the DATA ACL. You are required to +call the "spf" condition first in the ACLs, then the "dmarc_status" +condition. Putting this condition in the ACLs is required in order +for a DMARC check to actually occur. All of the variables are set +up before the DATA ACL, but there is no actual DMARC check that +occurs until a "dmarc_status" condition is encountered in the ACLs. + +The dmarc_status condition takes a list of strings on its +right-hand side. These strings describe recommended action based +on the DMARC check. To understand what the policy recommendations +mean, refer to the DMARC website above. Valid strings are: +.display +&'accept '& The DMARC check passed and the library recommends accepting the email. +&'reject '& The DMARC check failed and the library recommends rejecting the email. +&'quarantine '& The DMARC check failed and the library recommends keeping it for further inspection. +&'none '& The DMARC check passed and the library recommends no specific action, neutral. +&'norecord '& No policy section in the DMARC record for this sender domain. +&'nofrom '& Unable to determine the domain of the sender. +&'temperror '& Library error or dns error. +&'off '& The DMARC check was disabled for this email. +.endd +You can prefix each string with an exclamation mark to invert its +meaning, for example "!accept" will match all results but +"accept". The string list is evaluated left-to-right in a +short-circuit fashion. When a string matches the outcome of the +DMARC check, the condition succeeds. If none of the listed +strings matches the outcome of the DMARC check, the condition +fails. + +Of course, you can also use any other lookup method that Exim +supports, including LDAP, Postgres, MySQL, etc, as long as the +result is a list of colon-separated strings. + +Performing the check sets up information used by the +&%authresults%& expansion item. + +Several expansion variables are set before the DATA ACL is +processed, and you can use them in this ACL. The following +expansion variables are available: + +&$dmarc_status$& +.vindex &$dmarc_status$& +.cindex DMARC result +is a one word status indicating what the DMARC library +thinks of the email. It is a combination of the results of +DMARC record lookup and the SPF/DKIM/DMARC processing results +(if a DMARC record was found). The actual policy declared +in the DMARC record is in a separate expansion variable. + +&$dmarc_status_text$& +.vindex &$dmarc_status_text$& +is a slightly longer, human readable status. + +&$dmarc_used_domain$& +.vindex &$dmarc_used_domain$& +is the domain which DMARC used to look up the DMARC policy record. + +&$dmarc_domain_policy$& +.vindex &$dmarc_domain_policy$& +is the policy declared in the DMARC record. Valid values +are "none", "reject" and "quarantine". It is blank when there +is any error, including no DMARC record. + +. subsection + +By default, Exim's DMARC configuration is intended to be +non-intrusive and conservative. To facilitate this, Exim will not +create any type of logging files without explicit configuration by +you, the admin. Nor will Exim send out any emails/reports about +DMARC issues without explicit configuration by you, the admin (other +than typical bounce messages that may come about due to ACL +processing or failure delivery issues). + +In order to log statistics suitable to be imported by the opendmarc +tools, you need to: +.ilist +Configure the global setting dmarc_history_file +.next +Configure cron jobs to call the appropriate opendmarc history +import scripts and truncating the dmarc_history_file +.endlist + +In order to send forensic reports, you need to: +.ilist +Configure the global setting dmarc_forensic_sender +.next +Configure, somewhere before the DATA ACL, the control option to +enable sending DMARC forensic reports +.endlist + +. subsection + +Example usage: +.code +(RCPT ACL) + warn domains = +local_domains + hosts = +local_hosts + control = dmarc_disable_verify + + warn !domains = +screwed_up_dmarc_records + control = dmarc_enable_forensic + + warn condition = (lookup if destined to mailing list) + set acl_m_mailing_list = 1 + +(DATA ACL) + warn dmarc_status = accept : none : off + !authenticated = * + log_message = DMARC DEBUG: $dmarc_status $dmarc_used_domain + + warn dmarc_status = !accept + !authenticated = * + log_message = DMARC DEBUG: '$dmarc_status' for $dmarc_used_domain + + warn dmarc_status = quarantine + !authenticated = * + set $acl_m_quarantine = 1 + # Do something in a transport with this flag variable + + deny condition = ${if eq{$dmarc_domain_policy}{reject}} + condition = ${if eq{$acl_m_mailing_list}{1}} + message = Messages from $dmarc_used_domain break mailing lists + + deny dmarc_status = reject + !authenticated = * + message = Message from $dmarc_used_domain failed sender's DMARC policy, REJECT + + warn add_header = :at_start:${authresults {$primary_hostname}} +.endd + +.wen + + + + . //////////////////////////////////////////////////////////////////////////// . //////////////////////////////////////////////////////////////////////////// diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog index 22a38981b..293ff201a 100644 --- a/doc/doc-txt/ChangeLog +++ b/doc/doc-txt/ChangeLog @@ -183,6 +183,8 @@ JH/38 Bug 1395: Teach the DNS negative-cache about TTL value from the SOA in HS/05 Handle trailing backslash gracefully. (CVE-2019-15846) +JH/39 Promote DMARC support to mainline. + Exim version 4.92 ----------------- diff --git a/doc/doc-txt/OptionLists.txt b/doc/doc-txt/OptionLists.txt index abc09ece1..1618e4279 100644 --- a/doc/doc-txt/OptionLists.txt +++ b/doc/doc-txt/OptionLists.txt @@ -182,9 +182,9 @@ directory_transport string* unset redirect disable_ipv6 boolean false main 4.61 disable_logging boolean false routers 4.11 false transports 4.11 -dmarc_forensic_sender string unset main 4.82 if experimental_dmarc -dmarc_history_file string unset main 4.82 if experimental_dmarc -dmarc_tld_file string unset main 4.82 if experimental_dmarc +dmarc_forensic_sender string unset main 4.82 if experimental_dmarc, 4.93 mainline +dmarc_history_file string unset main 4.82 if experimental_dmarc, 4.93 mainline +dmarc_tld_file string unset main 4.82 if experimental_dmarc, 4.93 mainline dns_again_means_nonexist domain list unset main 1.89 dns_check_names_pattern string + main 2.11 dns_cname_loops integer 0 main 4.92 Set to 9 for older behaviour diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt index f748f6146..2b77d2647 100644 --- a/doc/doc-txt/experimental-spec.txt +++ b/doc/doc-txt/experimental-spec.txt @@ -390,239 +390,6 @@ Use a reasonable IP. eg. one the sending cluster actually uses. -DMARC Support --------------------------------------------------------------- - -DMARC combines feedback from SPF, DKIM, and header From: in order -to attempt to provide better indicators of the authenticity of an -email. This document does not explain the fundamentals, you -should read and understand how it works by visiting the website at -http://www.dmarc.org/. - -DMARC support is added via the libopendmarc library. Visit: - - http://sourceforge.net/projects/opendmarc/ - -to obtain a copy, or find it in your favorite rpm package -repository. If building from source, this description assumes -that headers will be in /usr/local/include, and that the libraries -are in /usr/local/lib. - -1. To compile Exim with DMARC support, you must first enable SPF. -Please read the Local/Makefile comments on enabling the SUPPORT_SPF -feature. You must also have DKIM support, so you cannot set the -DISABLE_DKIM feature. Once both of those conditions have been met -you can enable DMARC in Local/Makefile: - -EXPERIMENTAL_DMARC=yes -LDFLAGS += -lopendmarc -# CFLAGS += -I/usr/local/include -# LDFLAGS += -L/usr/local/lib - -The first line sets the feature to include the correct code, and -the second line says to link the libopendmarc libraries into the -exim binary. The commented out lines should be uncommented if you -built opendmarc from source and installed in the default location. -Adjust the paths if you installed them elsewhere, but you do not -need to uncomment them if an rpm (or you) installed them in the -package controlled locations (/usr/include and /usr/lib). - - -2. Use the following global options to configure DMARC: - -Required: -dmarc_tld_file Defines the location of a text file of valid - top level domains the opendmarc library uses - during domain parsing. Maintained by Mozilla, - the most current version can be downloaded - from a link at http://publicsuffix.org/list/. - See also util/renew-opendmarc-tlds.sh script. - The default for the option is currently - /etc/exim/opendmarc.tlds - -Optional: -dmarc_history_file Defines the location of a file to log results - of dmarc verification on inbound emails. The - contents are importable by the opendmarc tools - which will manage the data, send out DMARC - reports, and expire the data. Make sure the - directory of this file is writable by the user - exim runs as. - -dmarc_forensic_sender Alternate email address to use when sending a - forensic report detailing alignment failures - if a sender domain's dmarc record specifies it - and you have configured Exim to send them. - - If set, this is expanded and used for the - From: header line; the address is extracted - from it and used for the envelope from. - If not set, the From: header is expanded from - the dsn_from option, and <> is used for the - envelope from. - - Default: unset. - - -3. By default, the DMARC processing will run for any remote, -non-authenticated user. It makes sense to only verify DMARC -status of messages coming from remote, untrusted sources. You can -use standard conditions such as hosts, senders, etc, to decide that -DMARC verification should *not* be performed for them and disable -DMARC with a control setting: - - control = dmarc_disable_verify - -A DMARC record can also specify a "forensic address", which gives -exim an email address to submit reports about failed alignment. -Exim does not do this by default because in certain conditions it -results in unintended information leakage (what lists a user might -be subscribed to, etc). You must configure exim to submit forensic -reports to the owner of the domain. If the DMARC record contains a -forensic address and you specify the control statement below, then -exim will send these forensic emails. It's also advised that you -configure a dmarc_forensic_sender because the default sender address -construction might be inadequate. - - control = dmarc_enable_forensic - -(AGAIN: You can choose not to send these forensic reports by simply -not putting the dmarc_enable_forensic control line at any point in -your exim config. If you don't tell it to send them, it will not -send them.) - -There are no options to either control. Both must appear before -the DATA acl. - - -4. You can now run DMARC checks in incoming SMTP by using the -"dmarc_status" ACL condition in the DATA ACL. You are required to -call the spf condition first in the ACLs, then the "dmarc_status" -condition. Putting this condition in the ACLs is required in order -for a DMARC check to actually occur. All of the variables are set -up before the DATA ACL, but there is no actual DMARC check that -occurs until a "dmarc_status" condition is encountered in the ACLs. - -The dmarc_status condition takes a list of strings on its -right-hand side. These strings describe recommended action based -on the DMARC check. To understand what the policy recommendations -mean, refer to the DMARC website above. Valid strings are: - - o accept The DMARC check passed and the library recommends - accepting the email. - o reject The DMARC check failed and the library recommends - rejecting the email. - o quarantine The DMARC check failed and the library recommends - keeping it for further inspection. - o none The DMARC check passed and the library recommends - no specific action, neutral. - o norecord No policy section in the DMARC record for this - sender domain. - o nofrom Unable to determine the domain of the sender. - o temperror Library error or dns error. - o off The DMARC check was disabled for this email. - -You can prefix each string with an exclamation mark to invert its -meaning, for example "!accept" will match all results but -"accept". The string list is evaluated left-to-right in a -short-circuit fashion. When a string matches the outcome of the -DMARC check, the condition succeeds. If none of the listed -strings matches the outcome of the DMARC check, the condition -fails. - -Of course, you can also use any other lookup method that Exim -supports, including LDAP, Postgres, MySQL, etc, as long as the -result is a list of colon-separated strings. - -Performing the check sets up information used by the -${authresults } expansion item. - -Several expansion variables are set before the DATA ACL is -processed, and you can use them in this ACL. The following -expansion variables are available: - - o $dmarc_status - This is a one word status indicating what the DMARC library - thinks of the email. It is a combination of the results of - DMARC record lookup and the SPF/DKIM/DMARC processing results - (if a DMARC record was found). The actual policy declared - in the DMARC record is in a separate expansion variable. - - o $dmarc_status_text - This is a slightly longer, human readable status. - - o $dmarc_used_domain - This is the domain which DMARC used to look up the DMARC - policy record. - - o $dmarc_domain_policy - This is the policy declared in the DMARC record. Valid values - are "none", "reject" and "quarantine". It is blank when there - is any error, including no DMARC record. - -A now-redundant variable $dmarc_ar_header has now been withdrawn. -Use the ${authresults } expansion instead. - - -5. How to enable DMARC advanced operation: -By default, Exim's DMARC configuration is intended to be -non-intrusive and conservative. To facilitate this, Exim will not -create any type of logging files without explicit configuration by -you, the admin. Nor will Exim send out any emails/reports about -DMARC issues without explicit configuration by you, the admin (other -than typical bounce messages that may come about due to ACL -processing or failure delivery issues). - -In order to log statistics suitable to be imported by the opendmarc -tools, you need to: -a. Configure the global setting dmarc_history_file. -b. Configure cron jobs to call the appropriate opendmarc history - import scripts and truncating the dmarc_history_file. - -In order to send forensic reports, you need to: -a. Configure the global setting dmarc_forensic_sender. -b. Configure, somewhere before the DATA ACL, the control option to - enable sending DMARC forensic reports. - - -6. Example usage: -(RCPT ACL) - warn domains = +local_domains - hosts = +local_hosts - control = dmarc_disable_verify - - warn !domains = +screwed_up_dmarc_records - control = dmarc_enable_forensic - - warn condition = (lookup if destined to mailing list) - set acl_m_mailing_list = 1 - -(DATA ACL) - warn dmarc_status = accept : none : off - !authenticated = * - log_message = DMARC DEBUG: $dmarc_status $dmarc_used_domain - - warn dmarc_status = !accept - !authenticated = * - log_message = DMARC DEBUG: '$dmarc_status' for $dmarc_used_domain - - warn dmarc_status = quarantine - !authenticated = * - set $acl_m_quarantine = 1 - # Do something in a transport with this flag variable - - deny condition = ${if eq{$dmarc_domain_policy}{reject}} - condition = ${if eq{$acl_m_mailing_list}{1}} - message = Messages from $dmarc_used_domain break mailing lists - - deny dmarc_status = reject - !authenticated = * - message = Message from $dmarc_used_domain failed sender's DMARC policy, REJECT - - warn add_header = :at_start:${authresults {$primary_hostname}} - - - DSN extra information --------------------- If compiled with EXPERIMENTAL_DSN_INFO extra information will be added |