X-Git-Url: https://git.exim.org/exim.git/blobdiff_plain/617d39327e65b7fccc41a12b4a5e2940d6327c9f..1bca4f5fc7d74ba4ec1ced72eef8b806ae2be989:/doc/doc-txt/experimental-spec.txt?ds=sidebyside diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt index 4ed6f2518..43f14237b 100644 --- a/doc/doc-txt/experimental-spec.txt +++ b/doc/doc-txt/experimental-spec.txt @@ -430,14 +430,13 @@ package controlled locations (/usr/include and /usr/lib). 2. Use the following global settings to configure DMARC: -Optional: +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/. - If unset, "/etc/exim/opendmarc.tlds" (hardcoded) - is used. + See also util/renew-opendmarc-tlds.sh script. Optional: dmarc_history_file Defines the location of a file to log results @@ -525,6 +524,9 @@ 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: @@ -548,9 +550,8 @@ expansion variables are available: are "none", "reject" and "quarantine". It is blank when there is any error, including no DMARC record. - o $dmarc_ar_header - This is the entire Authentication-Results header which you can - add using an add_header modifier. +A now-redundant variable $dmarc_ar_header has now been withdrawn. +Use the ${authresults } expansion instead. 5. How to enable DMARC advanced operation: @@ -590,7 +591,6 @@ b. Configure, somewhere before the DATA ACL, the control option to warn dmarc_status = accept : none : off !authenticated = * log_message = DMARC DEBUG: $dmarc_status $dmarc_used_domain - add_header = $dmarc_ar_header warn dmarc_status = !accept !authenticated = * @@ -609,6 +609,8 @@ b. Configure, somewhere before the DATA ACL, the control option to !authenticated = * message = Message from $dmarc_used_domain failed sender's DMARC policy, REJECT + warn add_header = :at_start:${authresults {$primary_hostname}} + DSN extra information @@ -723,7 +725,7 @@ the queuefile driver. The transport only takes one option: * directory - This is used to specify the directory messages should be -copied to +copied to. Expanded. The generic transport options (body_only, current_directory, disable_logging, debug_print, delivery_date_add, envelope_to_add, event_action, group, @@ -791,16 +793,102 @@ standard header. Note that it would be wise to strip incoming messages of A-R headers that claim to be from our own . +There are three new variables: $arc_state, $arc_state_reason, $arc_domains: + + $arc_state One of pass, fail, none + $arc_state_reason (if fail, why) + $arc_domains colon-sep list of ARC chain domains, in chain order. + problematic elements may have empty list elements + $arc_oldest_pass lowest passing instance number of chain + +Example: + logwrite = oldest-p-ams: <${reduce {$lh_ARC-Authentication-Results:} \ + {} \ + {${if = {$arc_oldest_pass} \ + {${extract {i}{${extract {1}{;}{$item}}}}} \ + {$item} {$value}}} \ + }> + Receive log lines for an ARC pass will be tagged "ARC". Signing -- -arc_sign = : : +arc_sign = : : [ : ] An option on the smtp transport, which constructs and prepends to the message an ARC set of headers. The textually-first Authentication-Results: header is used as a basis (you must have added one on entry to the ADMD). - +Expanded as a whole; if unset, empty or forced-failure then no signing is done. +If it is set, all of the first three elements must be non-empty. + +The fourth element is optional, and if present consists of a comma-separated list +of options. The options implemented are + + timestamps Add a t= tag to the generated AMS and AS headers, with the + current time. + expire[=] Add an x= tag to the generated AMS header, with an expiry time. + If the value is an plain number it is used unchanged. + If it starts with a '+' then the following number is added + to the current time, as an offset in seconds. + If a value is not given it defaults to a one month offset. + +[As of writing, gmail insist that a t= tag on the AS is mandatory] + +Caveats: + * There must be an Authentication-Results header, presumably added by an ACL + while receiving the message, for the same ADMD, for arc_sign to succeed. + This requires careful coordination between inbound and outbound logic. + + Only one A-R header is taken account of. This is a limitation versus + the ARC spec (which says that all A-R headers from within the ADMD must + be used). + + * If passing a message to another system, such as a mailing-list manager + (MLM), between receipt and sending, be wary of manipulations to headers made + by the MLM. + + For instance, Mailman with REMOVE_DKIM_HEADERS==3 might improve + deliverability in a pre-ARC world, but that option also renames the + Authentication-Results header, which breaks signing. + + * Even if you use multiple DKIM keys for different domains, the ARC concept + should try to stick to one ADMD, so pick a primary domain and use that for + AR headers and outbound signing. + +Signing is not compatible with cutthrough delivery; any (before expansion) +value set for the option will result in cutthrough delivery not being +used via the transport in question. + + + + +REQUIRETLS support +------------------ +Ref: https://tools.ietf.org/html/draft-ietf-uta-smtp-require-tls-03 + +If compiled with EXPERIMENTAL_REQUIRETLS support is included for this +feature, where a REQUIRETLS option is added to the MAIL command. +The client may not retry in clear if the MAIL+REQUIRETLS fails (or was never +offered), and the server accepts an obligation that any onward transmission +by SMTP of the messages accepted will also use REQUIRETLS - or generate a +fail DSN. + +The Exim implementation includes +- a main-part option tls_advertise_requiretls; host list, default "*" +- an observability variable $requiretls returning yes/no +- an ACL "control = requiretls" modifier for setting the requirement +- Log lines and Received: headers capitalise the S in the protocol + element: "P=esmtpS" + +Differences from spec: +- we support upgrading the requirement for REQUIRETLS, including adding + it from cold, withing an MTA. The spec only define the sourcing MUA + as being able to source the requirement, and makes no mention of upgrade. +- No support is coded for the RequireTLS header (which can be used + to annul DANE and/or STS policiy). [can this be done in ACL?] + +Note that REQUIRETLS is only advertised once a TLS connection is acheived +(in contrast to STARTTLS). If you want to check the advertising, do something +like "swaks -s 127.0.0.1 -tls -q HELO". --------------------------------------------------------------