Xlbiff lets you preview new mail to decide if you want to read it
immediately.  Regular xbiff lets you know when you have mail but not what
it is.

Xlbiff lurks in the background, monitoring your mailbox file.  When
something shows up there, it invokes the scanCommand (MH's scan by
default), and displays the output in a window.  If more mail comes in, it
scans again and resizes accordingly.

If you're a Berkeley mail person, you can set scanCommand to:

	echo x | mail | grep "^.[NU]"

Or use the ``frm'' utility that is part of the Elm port as your
scanCommand.  A simular utility is the ``fromwho'' package, posted to
comp.sources.unix volume 25.