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.