What is Mail Exchange Record (MX Record)?
A mail exchange record (MX record) is a resource record or setting within the Domain Name System (DNS) that forwards e-mails to a specific mail server that accepts e-mails on behalf of a domain or from users. Within an MX record, you can set routing priorities using preference values for which the mail server is used when there are multiple servers.
Mail exchange records and other types of resource records are the basic information elements of DNS and are distinguished by type identification such as MX, NS, A, etc. along with a DNS class. These records have a certain period of validity before the information in them has to be updated by an authoritative name server.
In its simplest form, a domain can have a single mail server, that is, when a mail transfer agent (MTA) queries the MX records for www.something.com for a mail server and the DNS with only one mail server mail.something replies .com, even with a large preference number like 60, the MTA will select that single mail server for mail delivery. In this case it does not matter which preference number there is, as there is only one single mail server.