Domain Name System (DNS)

Mail Exchanger [MX] Record

A MX Record identifies the mail server(s) responsible for a domain name. When sending an e-mail to user@xyz.com, your mail server must first look up the MX Record for xyz.com to see which mail server actually handles mail for xyz.com (this could be mail.xyz.com - or someone else's mail server like mail.isp.com). Then it looks up the A Record for the mail server to connect to its IP-address.

A MX Record has a Preference number indicating the order in which the mail server should be used (only relevant when multiple MX Records are defined for the same domain name). Mail servers will attempt to deliver mail to the server with the lowest preference number first, and if unsuccessful continue with the next lowest and so on.