In the Domain Name System, an MX record is something that a domain uses to tell people and software the IP address of an email server. There can be more than one MX record for a domain. When there is more than one record, DNS uses a priority list that tells whatever is looking up the records to try the IP addresses in a certain order. For example, "example.com" might have a set of MX records that say for "mail.example.com" to try "127.0.0.5" first. If that try fails, another record will say to try "127.0.0.6". This behavior makes email more reliable.