mail  -  send mail to designated users

     mail [ -yn ] [ person ... ]

     Mail with no argument searches for a file called .mail,
     prints it if it is nonempty, then asks if it should be
     saved.  If the answer is y, the mail is added to mbox.
     Finally .mail is truncated to zero length.  To leave the
     mailbox untouched, hit `delete.'  The question can be
     answered on the command line with the argument `-y' or `-n'.

     When persons are named, mail takes the standard input up to
     an end of file and adds it to each person's .mail file.  The
     message is preceded by the sender's name and a postmark.

     A person is either a user name recognized by login (I), in
     which case the mail is sent to the default working directory
     of that user; or the path name of a directory, in which case
     .mail in that directory is used.

     When a user logs in he is informed of the presence of mail.
     No mail will be received from a sender to whom .mail is
     inaccessible or unwritable.

     /etc/passwd     to identify sender and locate persons
     /etc/utmp       to identify sender
     mbox            saved mail
     /tmp/m# temp file

     write (I)