This section outlines the basic steps needed to set up this machine as a mail server. The first step would be to give this machine a hostname. After that, you can specify a relay host, if needed. Relay hosts need to be created only if this machine cannot send mail directly to the Internet. If defined, the mail server will forward all outgoing mail to the relay host.
You should select a client restrictions policy for this mail server. These restrictions are applied to machines trying to send mail to our server. Client restrictions help reject illegitimate mail, mostly spam.