Mailwatch is a plugin for the Xfce 4 panel.

Features

    *   IMAP and Secure IMAP support
    *   POP3 and Secure POP3 support
    *   Local Mbox mailbox support
    *   Local Maildir mailbox support
    *   Local MH-Maildir mailbox support
    *   GMail support
    *   Fully multithreaded design: no panel lockups
    *   Informative new-message breakdown in tooltip
    *   Ability to run program on new messages or button click
    *   Informative logger to help track down mail connection problems

WWW:	http://spuriousinterrupt.org/projects/mailwatch