The comsat utility is the server process which receives reports of incoming mail and notifies users if they have requested this service. The comsat utility receives messages on a datagram port associated with the "biff" service specification (see services(5) and inetd(8)). The one line messages are of the form:
If the user specified is logged in to the system and the associated terminal has the owner execute bit turned on (by a "biff y"), the offset is used as a seek offset into the appropriate mailbox file and the first 7 lines or 560 characters of the message are printed on the users terminal. Lines which appear to be part of the message header other than the "From", "To", "Date", or "Subject" lines are not included in the displayed message.
If the user specified is logged in to the system and the associated terminal has the group execute bit turned on (by a "biff b"), two bell characters ( ASCII \007) are printed on the users terminal.
If mailbox-name omitted, standard mailbox assumed.