--- a/conf/acl.conf	Sun May 11 10:55:34 2014 +0200
+++ b/conf/acl.conf	Sun May 11 15:38:32 2014 +0200
@@ -7,9 +7,12 @@
 
     accept  domains = +local_domains
             local_parts = postmaster
-    ….
+    …
     require message = relaying denied
             domains = +local_domains
+
+    require message = unknown recipient
+            verify = recipient/callout=use_sender,defer_ok
     …
     accept