Electronic Mail, better known as email, is one of the most widely used forms of communication today. Millions of people use email every day, and chances are if you are reading this online, you fall into that category and probably even have more than one email address.
Electronic Mail configuration is the subject of many System Administration books. If you plan on doing anything beyond setting up one mailhost for your network, you need industrial strength help.
Some parts of email configuration are controlled in the Domain Name System (DNS). If you are going to run your own DNS server, be sure to read /etc/namedb and man -k named.