gbiff2 periodically checks for mail and displays headers when new mail has arrived. It relies on the GNOME and GTK libraries, but can be compiled and used with or without GNOME support. The protocols it supports are POP3, APOP, IMAP4, mh, qmail, and mailfile. Furthermore, gbiff2 is fully configurable, with a lot of options like polltime, poptime, sounds, mail reader, mailbox title, etc.
gnubiff is a mail notification program that periodically checks for mail and displays headers when new mail has arrived. It supports multiple mailboxes, pop3, apop, imap4, mh, qmail and mailfile, SSL and certificates, GNOME with integration to the panel, GTK standalone, automatic detection of mailbox format, mail header and content display, PNG animation, HIG 2.0 compliance, and spam filtering.