3.1.5.4. MX

The MX record specifies the address of the mail server that should receive incoming mail for the given domain. The address can be a domain or subdomain, but an IP address cannot be used. The domain or subdomain from the address must have an A record.

Each MX record has its own priority. It is used only in case the servers are unavailable. For example, if there are two records with priorities 10 and 20, the mail will first be directed to the server from the record with priority 10, and only if it is unavailable will it be sent to the server from the record with priority 20.