Biff may be obsolete, but if you use X try xbuffy. It's VERY nice. I
use procmail to automatically sort mail to a set of folders (currently
36), and xbuffy monitors them all continuously, showing in inverted
video those who have new msgs. and the number of them. If you click on
the box of the folder it pops up a windows showing the sender and
subject of the msgs. It can be configured to pop up the window with
the list of msgs. for certain important folders, so that you don't
miss you boss calling you :-)
Just for completeness, I use VM under emacs to read the msgs. sorted
by procmail. The whole scheme takes 3 config files, but for large
numbers of msgs. and folders it pays off.
PS: I recommend version 3.3 of xbuffy. It's unreleased, but can be
obtained from the author. I can give the details to those interested.