1 files changed, 15 insertions, 0 deletions
diff --git a/src/mailman/interfaces/member.py b/src/mailman/interfaces/member.py
index 87ad19c83..66cf61581 100644
--- a/src/mailman/interfaces/member.py
+++ b/src/mailman/interfaces/member.py
@@ -28,6 +28,7 @@ __all__ = [
     'MemberRole',
     'MembershipError',
     'MembershipIsBannedError',
+    'NotAMemberError',
     ]
 
 
@@ -105,6 +106,20 @@ class MembershipIsBannedError(MembershipError):
             self._address, self._mlist)
 
 
+@error_status(400)
+class NotAMemberError(MembershipError):
+    """The address is not a member of the mailing list."""
+
+    def __init__(self, mlist, address):
+        super(NotAMemberError, self).__init__()
+        self._mlist = mlist
+        self._address = address
+
+    def __str__(self):
+        return '{0} is not a member of {1.fqdn_listname}'.format(
+            self._address, self._mlist)
+
+
 
 class IMember(Interface):
     """A member of a mailing list."""