ARC: on the smtp transport option take empty or forced-fail to disable signing

diff --git a/doc/doc-txt/experimental-spec.txt b/doc/doc-txt/experimental-spec.txt
index ce140c553f1fdf3948919949cb0c145b1168ff08..149598ee8934b5465983a5271cd9634a65688bb6 100644 (file)
--- a/doc/doc-txt/experimental-spec.txt
+++ b/doc/doc-txt/experimental-spec.txt
@@ -799,6 +799,7 @@ 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; if unset, empty or forced-failure then no signing is done.
 
 
 

diff --git a/src/src/transports/smtp.c b/src/src/transports/smtp.c
index c4a6c028350eec39448da697281b1c7a15eb6240..23083f5d879c829a4ed5d7d0ff2a851fa696fb5d 100644 (file)
--- a/src/src/transports/smtp.c
+++ b/src/src/transports/smtp.c
@@ -2999,15 +2999,21 @@ else
     uschar * s = sx.ob->arc_sign;
     if (s)
       {
-      if (!(sx.ob->dkim.arc_signspec = expand_string(s)))
+      if (!(sx.ob->dkim.arc_signspec = s = expand_string(s)))
        {
-       message = US"failed to expand arc_sign";
-       sx.ok = FALSE;
-       goto SEND_FAILED;
+       if (!expand_string_forcedfail)
+         {
+         message = US"failed to expand arc_sign";
+         sx.ok = FALSE;
+         goto SEND_FAILED;
+         }
+       }
+      else if (*s)
+       {
+       /* Ask dkim code to hash the body for ARC */
+       (void) arc_ams_setup_sign_bodyhash();
+       sx.ob->dkim.force_bodyhash = TRUE;
        }
-      /* Ask dkim code to hash the body for ARC */
-      (void) arc_ams_setup_sign_bodyhash();
-      sx.ob->dkim.force_bodyhash = TRUE;
       }
     }
 # endif