1 files changed, 33 insertions, 0 deletions

diff --git a/src/mailman/utilities/email.py b/src/mailman/utilities/email.py
index 4b1023ce1..38c9980a2 100644
--- a/src/mailman/utilities/email.py
+++ b/src/mailman/utilities/email.py
@@ -21,10 +21,17 @@ from __future__ import absolute_import, unicode_literals
 
 __metaclass__ = type
 __all__ = [
+    'add_message_hash',
     'split_email',
     ]
 
 
+from base64 import b32encode
+from hashlib import sha1
+
+
+
+
 def split_email(address):
     """Split an email address into a user name and domain.
 
@@ -39,3 +46,29 @@ def split_email(address):
         # There was no at-sign in the email address.
         return local_part, None
     return local_part, domain.split('.')
+
+
+def add_message_hash(msg):
+    """Add a X-Message-ID-Hash header derived from Message-ID.
+
+    This function works by side-effect; the original message is mutated.  Any
+    existing X-Message-ID-Headers are deleted if a Message-ID header is
+    found.  If no Message-ID header is found, the original message is not
+    modified.
+
+    :param msg: An email message
+    :type msg: `email.message.Message` or derived
+    """
+    message_id = msg.get('message-id')
+    if message_id is None:
+        return
+    # The angle brackets are not part of the Message-ID.  See RFC 2822
+    # and http://wiki.list.org/display/DEV/Stable+URLs
+    if message_id.startswith('<') and message_id.endswith('>'):
+        message_id = message_id[1:-1]
+    else:
+        message_id = message_id.strip()
+    digest = sha1(message_id).digest()
+    message_id_hash = b32encode(digest)
+    del msg['x-message-id-hash']
+    msg['X-Message-ID-Hash'] = message_id_hash