diff --git a/Lib/mailbox.py b/Lib/mailbox.py
index 98e61f2..b1c082d 100755
--- a/Lib/mailbox.py
+++ b/Lib/mailbox.py
@@ -15,7 +15,7 @@
         self.factory = factory
 
     def __iter__(self):
-        return self
+        return iter(self.next, None)
 
     def next(self):
         while 1:
@@ -195,7 +195,7 @@
         self.factory = factory
 
     def __iter__(self):
-        return self
+        return iter(self.next, None)
 
     def next(self):
         if not self.boxes:
@@ -226,7 +226,7 @@
         self.boxes = boxes
 
     def __iter__(self):
-        return self
+        return iter(self.next, None)
 
     def next(self):
         if not self.boxes: