xlbiff binary package in Ubuntu Xenial amd64

 Xlbiff lurks in the background, monitoring your mailbox file (normally
 /var/spool/mail/<yourusername>). When something shows up there, it
 invokes the MH scan(1) command and displays the output in a window.
 If more mail comes in, it scans again and resizes accordingly.
 .
 Clicking the left mouse button anywhere in the window causes it to
 vanish. It will also vanish if you inc(1) and the mailbox becomes
 empty. Xlbiff is modeled after xconsole -- its job is to sit invisibly
 and pop up only when something demands your attention.

Source package