2 files changed, 14 insertions, 3 deletions

diff --git a/src/mailman/email/message.py b/src/mailman/email/message.py
index ebfef9d9b..26bc35b78 100644
--- a/src/mailman/email/message.py
+++ b/src/mailman/email/message.py
@@ -93,9 +93,10 @@ class Message(email.message.Message):
                                if envelope_sender is not None
                                else '')
             else:
-                field_values = self.get_all(header, [])
-                senders.extend(address.lower() for (display_name, address)
-                               in email.utils.getaddresses(field_values))
+                for field_value in self.get_all(header, []):
+                    # Convert the header to str in case it's a Header instance.
+                    name, address = email.utils.parseaddr(str(field_value))
+                    senders.append(address.lower())
         # Filter out None and the empty string, and convert to unicode.
         clean_senders = []
         for sender in senders:
diff --git a/src/mailman/email/tests/test_message.py b/src/mailman/email/tests/test_message.py
index 3ec099904..c23d37f7f 100644
--- a/src/mailman/email/tests/test_message.py
+++ b/src/mailman/email/tests/test_message.py
@@ -19,6 +19,7 @@
 
 import unittest
 
+from email.header import Header
 from email.parser import FeedParser
 from mailman.app.lifecycle import create_list
 from mailman.email.message import Message, UserNotification
@@ -52,6 +53,9 @@ class TestMessage(unittest.TestCase):
 
 
 class TestMessageSubclass(unittest.TestCase):
+
+    layer = ConfigLayer
+
     def test_i18n_filenames(self):
         parser = FeedParser(_factory=Message)
         parser.feed("""\
@@ -79,3 +83,9 @@ Test content
         except TypeError as error:
             self.fail(error)
         self.assertEqual(filename, u'd\xe9jeuner.txt')
+
+    def test_senders_header_instances(self):
+        msg = Message()
+        msg['From'] = Header('test@example.com')
+        # Make sure the senders property does not fail
+        self.assertEqual(msg.senders, ["test@example.com"])