biff — Be notified if mail arrives and who it is from
biff informs the system whether you want to be notified when mail arrives during the current terminal session.
When mail notification is enabled, the header and first few lines of the message will be printed on your screen whenever mail arrives. A
command is often included in the file .login or .profile to be executed at each login.
Biff operates asynchronously. For synchronous notification use the MAIL variable of sh or the mail variable of csh.
csh, mail, sh, comsat
The biff command appeared in BSD 4.0.