This document does not deal with exchanging mail messages between local machine and other nodes (inside a local area network or over the internet). This exchange should be carried out by messages transfer agents (MTAs) such as
smail ftp://ftp.planix.com/pub/Smail, etc.
In this document it is presupposed that this method of send/receive messages outside of the local computer is already installed and working in a correct way. If you can send a message and read your mail with the
$ mail -s <subject> <email@example.com>
write here the text, and finish with an alone point in the next line
you must have installed any type of MTA that is doing the messages transfer. In other way, you can get documentation about setting it up in the manual pages of smail:
$ man smail
or the MTA that you have, and fetchmail:
$ man fetchmail
or in other similar document that makes reference to those programs.