ARC: cutthrough delivery may not be used with ARC signing

[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 4ed6f2518ede4ceb7f72ed602a10760efcbae2de..4e244ac5fe93ffd83a80e0b8e3a0d687df86c83e 100644 (file)
--- a/doc/doc-txt/experimental-spec.txt
+++ b/doc/doc-txt/experimental-spec.txt
@@ -430,14 +430,12 @@ 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.
 
 Optional:
 dmarc_history_file  Defines the location of a file to log results
@@ -525,6 +523,9 @@ 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 +549,8 @@ 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+A now-redundant variable $dmarc_ar_header has now been withdrawn.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 +590,6 @@ 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 +608,8 @@ 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 +724,7 @@ 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,
@@ -791,6 +792,8 @@ standard header.
        Note that it would be wise to strip incoming messages of A-R headers
        that claim to be from our own <admd-identifier>.
 
+There are two new variables: $arc_state and $arc_state_reason.
+
 Receive log lines for an ARC pass will be tagged "ARC".
 
 
@@ -800,6 +803,26 @@ 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).
+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.