biff binary package in Ubuntu Focal amd64

 biff is a small program that prints a message to your terminal
 when new email arrives. Actually, the message is printed by
 the comsat daemon, and biff just enables/disables the u+x
 permission flag for the terminal, which comsat uses to determine
 whether or not to write to your terminal.
 .
 biff is mainly of historic interest, since there are much better
 alternatives (such as xlbiff and gbuffy) that are network-aware and
 do not require a daemon. Although there are no known security
 problems, running additional services is often considered risky.
 .
 By default, the biff service is disabled. To use biff email
 notification, you must enable this service by running 'update-inetd
 --enable biff' after the package is installed. You may also need
 to modify the configuration of your mail transport agent to enable
 comsat notification.

Source package