LetterBox is a POP3 e-mail notification program that sits quietly in your System Tray and, at a preset interval, checks to see whether any e-mail has arrived for you. Fully configurable. Bundles of features - plays WAV files; runs your e-mail client or whatever when new e-mail is found; support for multiple mailboxes; delete-off-server (for getting rid of spam etc.); automatic delete-off-server according to rules you specify and so on. Can be set to check for new e-mail only when you're already on-line so that it doesn't keep dialing up when you don't want it to.