X-Git-Url: https://git.exim.org/users/heiko/exim.git/blobdiff_plain/6372d4c990f39ba6ad84a91af0a3a61a63bd50a3..9122c6523b5c178a0ab4e28115e15179b1e6dea6:/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 5c8231123..aa93e07bf 100644
--- a/doc/doc-txt/experimental-spec.txt
+++ b/doc/doc-txt/experimental-spec.txt
@@ -793,7 +793,21 @@ 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".
 
@@ -805,7 +819,7 @@ 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
@@ -824,12 +838,18 @@ 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.