MX - DNS Record

An MX record or Mail exchanger record is a type of resource record in the Domain Name System (DNS) specifying how Internet e-mail should be routed using the Simple Mail Transfer Protocol (SMTP). Each MX record contains a preference and a host name, so that the collection of MX records for a given domain name point to the servers that should receive e-mail for that domain, and their priority relative to each other.
MX records are used to notify users where email directed to a domain name should be sent.
The Mail Exchange (MX) record identifies the server to which e-mail is directed. It also contains a priority field so that mail can be directed to multiple servers in a prescribed order.