--- f:/MM_bzr/2.1/Mailman/Handlers/CookHeaders.py	2008-06-17 17:35:26.000000000 -0700
+++ f:/test-mailman/Mailman/Handlers/CookHeaders.py	2010-09-20 07:29:10.281250000 -0700
@@ -136,6 +136,11 @@
             orig = msg.get_all('reply-to', [])
             for pair in getaddresses(orig):
                 add(pair)
+            # If there was no Reply-To, add the From: or Sender: address(es)
+            if not orig:
+                for pair in getaddresses(
+                        msg.get_all('from', msg.get_all('sender', []))):
+                    add(pair)
         # Set Reply-To: header to point back to this list.  Add this last
         # because some folks think that some MUAs make it easier to delete
         # addresses from the right than from the left.