the standard input up to an end-of-file and appends it to each user's mail file (mailbox). This program is intended to be used by sendmail(1M) as a mail delivery agent for local mail. It
is not a user interface agent.
Messages are appended to the user's mail file in the /var/mail directory. The user must be a valid user name.
Each delivered mail message in the mailbox is preceded by a "Unix From line" with the following format:
From sender_address time_stamp
The sender_address is extracted from the SMTP envelope address (the envelope address is specified with the -f option).
A trailing blank line is also added to the end of each message.
The mail files are locked with a .lock file while mail is appended.
The mail files are created with mode 660, owner is set to recipient, and group is set to mail. If the ``biff'' service is returned by getservbyname(3SOCKET), the biff server is notified of delivered mail. This program also computes the Content-Length: header which will be used by the mailbox reader to mark the message boundary.