MX records specify which mail servers are responsible for a particular domain. This entry is not mandatory, and as with the A record several entries may be made. One special feature is $priority numbers, which provide information to the querying mail server about which mail server should be used first. The next entry is tried only when the mail server with the highest priority is not available. The priority of $priority numbers rises in opposition to the value of the number, meaning that lower numbers have a higher priority.

Another special feature is that only domains may be entered for mail servers. An entry referencing an IP results in an error.