What is an MX record?
An “MX” (Mail eXchanger) record maps a domain (example.com) to a mail server that is responsible for receiving email for the domain. It tells other “sending” mail servers where they should deliver your email.
Multiple records and priority
Multiple MX records are supported (and recommended) for redundancy and load balancing. A priority value determines which servers should be sent to first. Lower values mean higher priority. e.g. 5 is a higher priority than 10.
Example
example.com MX mail1.tibus.net 5
example.com MX mail2.tibus.net 10