ARC: Fix signing for case when DKIM signing failed

[exim.git] / doc / doc-txt / experimental-spec.txt

diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt
index ce140c553f1fdf3948919949cb0c145b1168ff08..0eeb2275897d9783a03d1f2f8c459af84d48c2ce 100644 (file)
--- a/doc/doc-txt/experimental-spec.txt
+++ b/doc/doc-txt/experimental-spec.txt
@@ -436,6 +436,7 @@ dmarc_tld_file      Defines the location of a text file of valid
                     during domain parsing. Maintained by Mozilla,
                     the most current version can be downloaded
                     from a link at http://publicsuffix.org/list/.
                     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.

 
 Optional:
 dmarc_history_file  Defines the location of a file to log results
 
 Optional:
 dmarc_history_file  Defines the location of a file to log results


@@ -523,6 +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.
 
 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:
 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:


@@ -587,7 +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
   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 = *
 
   warn    dmarc_status   = !accept
           !authenticated = *


@@ -606,6 +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
 
           !authenticated = *
           message        = Message from $dmarc_used_domain failed sender's DMARC policy, REJECT
 

+  warn    add_header     = :at_start:${authresults {$primary_hostname}}
+

 
 
 DSN extra information
 
 
 DSN extra information


@@ -720,7 +725,7 @@ the queuefile driver.
 The transport only takes one option:
 
 * directory - This is used to specify the directory messages should be
 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,
 
 The generic transport options (body_only, current_directory, disable_logging,
 debug_print, delivery_date_add, envelope_to_add, event_action, group,


@@ -799,6 +804,26 @@ arc_sign = <admd-identifier> : <selector> : <privkey>
 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).
 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 three elements must be non-empty.
+
+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.
+ * 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.