diff -r 184ddd9acd5a Lib/mailbox.py
--- a/Lib/mailbox.py	Wed Apr 06 09:35:57 2011 -0400
+++ b/Lib/mailbox.py	Wed Apr 06 22:29:41 2011 +0200
@@ -76,7 +76,13 @@
         if not self._factory:
             return self.get_message(key)
         else:
-            return self._factory(self.get_file(key))
+            file = self.get_file(key)
+            message = self._factory(file)
+            try:
+                file.close()
+            except AttributeError:
+                del file
+            return message
 
     def get_message(self, key):
         """Return a Message representation or raise a KeyError."""