1 files changed, 6 insertions, 3 deletions

diff --git a/src/mailman/archiving/prototype.py b/src/mailman/archiving/prototype.py
index b5df11f78..73c296b5d 100644
--- a/src/mailman/archiving/prototype.py
+++ b/src/mailman/archiving/prototype.py
@@ -58,10 +58,13 @@ class Prototype:
     @staticmethod
     def permalink(mlist, msg):
         """See `IArchiver`."""
-        # It is the LMTP server's responsibility to ensure that the message
-        # has a X-Message-ID-Hash header.  If it doesn't then there's no
+        # It is the LMTP server's responsibility to ensure that the message has
+        # a Message-ID-Hash header.  For backward compatibility, fall back to
+        # X-Message-ID-Hash.  If the message has neither, then there's no
         # permalink.
-        message_id_hash = msg.get('x-message-id-hash')
+        message_id_hash = msg.get('message-id-hash')
+        if message_id_hash is None:
+            message_id_hash = msg.get('x-message-id-hash')
         if message_id_hash is None:
             return None
         if isinstance(message_id_hash, bytes):