MX 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. The host name contained in an MX record must have an address, i.e. an A or AAAA DNS record. CNAME aliases are prohibited in an MX record data, while CNAME is allowed for the MX record label, that is for the domain name leading to the MX record itself.[1] It is also not permitted to use an IP address directly in an MX record;[2] while some mail servers will send mail to domains with IP-based MX records, many (most notably Exim) will refuse to do so.
