GBuffy will poll multiple mailboxes for new mail. It will list the
number of new messages in each mailbox you configure. It will also
highlight the mailboxes which have new mail. Pressing the left mouse
button on a mailbox with new mail will display the Sender and Subject
of each new message. Additionally, GBuffy will display the X-Face
header for messages which have them. Pressing the middle mouse button
on a mailbox will launch the configured command, generally a command
to read the mailbox with your favorite mailreader. Pressing the right
mouse button will bring up the configure menu.
   
GBuffy is currently capable of watching MBOX, MMDF, Maildir and MH
Folders.  This version also supports IMAP4rev1 and NNTP with XOVER.
Support for an external program for notification is planned.

WWW: http://www.fiction.net/blong/programs/gbuffy/