MX records or mail exchange 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.
A MX record is a type of DNS record which is responsible for accepting incoming email and routing it to a specified mail server, based on the information in the record.
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.