Also, add a clause to the big-if to handle message/delivery-status
content types. These create a message with subparts that are
Message instances, which best represent the header blocks of this
content type.
<http://sf.net/projects/mimelib>. There /are/ API differences between
mimelib and email, but most of the implementations are shared (except
where cool Py2.2 stuff like generators are used).