Here is a small Python script to expire junk mail in an IMAP mailbox.
Apple Mail can automatically delete old junk mail, but I also use KMail and SquirrelMail, and it’s often a long wait between the times I load up Mail, so I need something else. It requires Python 2.4 (perhaps earlier, but I’ve not tried it), and that’s it. Run it with a --help to get started.
Incidentally, the script is also in a Bazaar repository, and you can branch it if you want:
bzr branch \
http://www.premolo.net/~gavin/Scripts
Right now the script doesn’t care about SSL (I run it on the same box as my Courier IMAP server) and it uses CRAM-MD5 authentication which may not be to your taste. It’s not had a lot of testing either, so be careful, and take some backups first :-) It’s in the public domain though, so happy hacking, and I’m more than willing to merge patches.