diff -ruN mailman-2.1.12-a/Mailman/Handlers/CookHeaders.py mailman-2.1.12-b/Mailman/Handlers/CookHeaders.py
--- mailman-2.1.12-a/Mailman/Handlers/CookHeaders.py	2009-02-23 22:23:35.000000000 +0100
+++ mailman-2.1.12-b/Mailman/Handlers/CookHeaders.py	2009-07-28 12:19:54.000000000 +0200
@@ -215,8 +215,6 @@
         # Add this header if we're archiving
         if mlist.archive:
             archiveurl = mlist.GetBaseArchiveURL()
-            if archiveurl.endswith('/'):
-                archiveurl = archiveurl[:-1]
             headers['List-Archive'] = '<%s>' % archiveurl
     # First we delete any pre-existing headers because the RFC permits only
     # one copy of each, and we want to be sure it's ours.