Add entry for the mailbox fixups.

Doc/whatsnew/3.2.rst

@@ -2144,6 +2144,34 @@ parameters, the return types will also be an ASCII-encoded byte strings:
 (Work by Nick Coghlan, Dan Mahn, and Senthil Kumaran in :issue:`2987`,
 :issue:`5468`, and :issue:`9873`.)
 
+mailbox
+-------
+
+Thanks to a concerted effort by R. David Murray, the :mod:`mailbox` module has
+been fixed for Python 3.2.  The challenge was that mailbox had been originally
+designed with a text interface, but email messages are best represented with
+:class:`bytes` because various parts of a message may have different encodings.
+
+The solution harnessed the :mod:`email` package's binary support for parsing
+arbitrary email messages.  In addition, the solution required a number of API
+changes.
+
+As expected, the :meth:`~mailbox.Mailbox.add` method for
+:class:`mailbox.Mailbox` objects now accepts binary input.
+
+:class:`~io.StringIO` and text file input are deprecated.  Also, string input
+will fail early if non-ASCII characters are used.  Previously it would fail when
+the email was processed in a later step.
+
+There is also support for binary output.  The :meth:`~mailbox.Mailbox.get_file`
+method now returns a file in the binary mode (where it used to incorrectly set
+the file to text-mode).  There is also a new :meth:`~mailbox.Mailbox.get_bytes`
+method that returns a :class:`bytes` representation of a message corresponding
+to a given *key*.
+
+(Contributed by R. David Murray with efforts from Steffen Daode Nurpmeso and
+Victor Stinner in :issue:`9124`.)
+
 turtledemo
 ----------