Bad email addresses cause all undelivered mail to be returned to the sender. For the owner of at the email discussion lists (Dave Houldershaw at Birkbeck), this can mean a number bounces in the mailbox, and this will become more problematic as the course hots up. `Offenders' will be listed here, although they may simply not know, and suspect we have forgotten them :( The causes are sometimes beyond anybody's control (machine outages, superhighway roadworks, upgrades, departmental moves, etc).