diff --git a/Lib/mailbox.py b/Lib/mailbox.py
--- a/Lib/mailbox.py
+++ b/Lib/mailbox.py
@@ -382,7 +382,7 @@
     def get_file(self, key):
         """Return a file-like representation or raise a KeyError."""
         f = open(os.path.join(self._path, self._lookup(key)), 'rb')
-        return _ProxyFile(f)
+        return _ProxyFile(f, close=True)
 
     def iterkeys(self):
         """Return an iterator over keys."""
@@ -1032,7 +1032,7 @@
                 raise KeyError('No message with key: %s' % key)
             else:
                 raise
-        return _ProxyFile(f)
+        return _ProxyFile(f, close=True)
 
     def iterkeys(self):
         """Return an iterator over keys."""
@@ -1867,13 +1867,15 @@
 class _ProxyFile:
     """A read-only wrapper of a file."""
 
-    def __init__(self, f, pos=None):
+    def __init__(self, f, pos=None, close=False):
         """Initialize a _ProxyFile."""
         self._file = f
         if pos is None:
             self._pos = f.tell()
         else:
             self._pos = pos
+        self._do_close = close
+        self._is_open = True
 
     def read(self, size=None):
         """Read bytes."""
@@ -1919,9 +1921,11 @@
 
     def close(self):
         """Close the file."""
-        if hasattr(self._file, 'close'):
+        if self._do_close:
+            self._do_close = False
             self._file.close()
-        del self._file
+            del self._file
+        self._is_open = False
 
     def _read(self, size, read_method):
         """Read size bytes using read_method."""
@@ -1953,7 +1957,7 @@
 
     @property
     def closed(self):
-        return self._file.closed
+        return not self._is_open
 
 
 class _PartialFile(_ProxyFile):
@@ -1988,11 +1992,6 @@
             size = remaining
         return _ProxyFile._read(self, size, read_method)
 
-    def close(self):
-        # do *not* close the underlying file object for partial files,
-        # since it's global to the mailbox object
-        del self._file
-
 
 def _lock_file(f, dotlock=True):
     """Lock file f using lockf and dot locking."""