X-Git-Url: https://git.exim.org/users/heiko/exim.git/blobdiff_plain/9604413b16bf7270395b92690ef429dca4a14eee..9122c6523b5c178a0ab4e28115e15179b1e6dea6:/doc/doc-txt/experimental-spec.txt

diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt
index 1a0ece574..aa93e07bf 100644
--- 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/.
+                    See also util/renew-opendmarc-tlds.sh script.
 
 Optional:
 dmarc_history_file  Defines the location of a file to log results
@@ -792,19 +793,70 @@ 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.
+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 = <admd-identifier> : <selector> : <privkey>
+arc_sign = <admd-identifier> : <selector> : <privkey> [ : <options> ]
 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.
+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[=<val>]	Add an x= tag to the generated AMS header, with an expiry time.
+			If the value <val> 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.