This is an implementation of a fast and smart algorithm for threading mail messages, as described by Jamie Zawinski at http://www.jwz.org/doc/threading.html. Don't send problems with this code to him, though; instead contact the author at amk@amk.ca, or bring it up on the oedipus-devel list at SourceForge. This code is under a BSD-style license; see the LICENSE file for the full text. --amk