Mail Exchanger (MX) records are used to directs email to a mail server according to the domain owners’ preference.
These preferences should be routed in accordance with Simple Mail Transfer Protocol (SMTP, the standard protocol for all email.)
The MX record itself specifies which server(s) to attempt to use to deliver mail to when this type of request is made to the domain.
Some email providers have only one MX record and some have well over two. The number of MX entries you will need to create depends largely on the mail provider and how they expect the load on these email servers to be handled.
The MX record differs from A Records and CNAMEs in the way that they also require a “priority” value as a part of their entry. The priority number is used to indicate which of the servers listed as MX records it should attempt to use first.
NB: The MX record with the lower priority number is the first to be tried for email delivery. If this server is unable to handle the mail request, the next lowest priority number is used.