diff --git a/lib/nntp/tiny/message.py b/lib/nntp/tiny/message.py
index e34bbee..9110d9a 100644
--- a/lib/nntp/tiny/message.py
+++ b/lib/nntp/tiny/message.py
@@ -348,7 +348,8 @@ class Message(DatabaseTable):
         current = self.message_id
 
         if current is None:
-            remote = sender.split('@', 2)[1]
+            parts  = sender.split('@', 2)
+            remote = 'unknown.host' if len(parts) == 0 else parts[1]
 
             self.message_id = '<%s@%s>' % (
                 str(uuid.uuid4()),