UNIX® Shells by Example, Third Edition

mail—mail, rmail—read mail or send mail to users

Sending mail mail [ –tw ] [ –m message_type ] recipient... rmail [ –tw ] [ –m message_type ] recipient...Reading mail mail [ –ehpPqr ] [ –f filename ]Forwarding mail mail –F recipient...Debugging mail [ –x debug_level ] [ other_mail_options ] recipient... mail [ –T mailsurr_file ] recipient...

A recipient is usually a username recognized by login. When recipients are named, mail assumes a message is being sent. It reads from the standard input up to an end-of-file (Ctrl-D), or if reading from a terminal, until it reads a line consisting of just a period. When either of those indicators is received, mail adds the letter to the mailfile for each recipient.