diff options
Diffstat (limited to 'doc/doc-txt/experimental-spec.txt')
| -rw-r--r-- | doc/doc-txt/experimental-spec.txt | 233 |
1 files changed, 0 insertions, 233 deletions
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 |