comsat is the server process which receives reports of incoming mail and notifies users if they have requested this service.
comsat 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:
user@mailbox-offset
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 user's terminal. Lines which appear to be part of the message header other than the “From” or “Subject” lines are not included in the displayed message.