What is MX Record, how many XR Record are there?

An MX (Mail eXchange) record will redirect email sent to any user's machine (, for example) to a designated mailhost. It tells the MDA where to route email.

A mail exchange record(MX record) is a type of resource record in the DNS that specifies a mail server  responsible for accepting email messages on behalf of a recipient's domain, and a preference value used to prioritize mail delivery if multiple mail servers are available. The set of MX records of a domain name specifies how email should be routed with the Simple Mail Transfer Protocol (SMTP).

MX stands for Mail exchange (MX).its specify and prioritize the incoming mail servers that receive email messages sent to your domain name. you can prioritize the mail server for example : mx5,mx10, 

A mail exchanger record (MX record) is a type of resource record in the Domain Name System that specifies a mail server responsible for accepting email messages on behalf of a recipient's domain, and a preference value used to prioritize mail delivery if multiple mail servers are available.