Before you can run any of the mail server programs (normally called an MTA mail transfer agent) you must make a few simple configuration changes to your DNS file on the Internet server. Look back at Chapter 2 to find out more about the DNS file and its records.

The first step is to configure your local DNS file to describe the correct mail routing for your server. The DNS contains the registered domain name and IP address for your Web server; now you must add lines to register your new MTA. These are called MX records and tell the server where to find the utility that will handle incoming and outgoing mail.

A typical new record in the DNS file to manage e-mail would be:

  mycompany.com. IN MX 10 mail.mycompany.com.

With this record in place, any e-mail to USER@mycompany.com is delivered to USER@mail.mycompany.com. The MTA (sendmail in this case) will ask the DNS for its MX record to tell it how to deal with mail without this record, nothing will work!