--- /usr/local/mailman/Mailman/Handlers/CookHeaders.py-dist	2008-08-03 11:19:50.000000000 +0900
+++ /usr/local/mailman/Mailman/Handlers/CookHeaders.py	2008-10-01 13:59:34.000000000 +0900
@@ -238,6 +238,10 @@
     prefix = mlist.subject_prefix.strip()
     if not prefix:
         return
+    # overwrite message-id.
+    msg['X-Original-Message-ID'] = msg.get('message-id', '')
+    del msg['message-id']
+    msg['Message-ID'] = Utils.unique_message_id(mlist)
     subject = msg.get('subject', '')
     # Try to figure out what the continuation_ws is for the header
     if isinstance(subject, Header):