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More about 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 priority 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.

• CNAME aliases are prohibited in an MX record data,

• The host name contained in an MX record must have an address, i.e. an A or AAAA DNS record.

• Some mailservers will send mail to domains with IP-based MX records, many (most notably Exim) will refuse to do so.

• The sending mail transfer agent makes a DNS query requesting the MX records.

• The sending agent then attempts to establish an SMTP connection to one of these servers, starting with the one with the smallest preference number.

• If there is more than one entry with the same preference number, all of those must be tried before moving on to lower-priority entries.

• One technique used to distribute the load of incoming mail over an array of servers is to return the same preference number for each server in the set.

• The MX mechanism does not grant the ability to provide mail service on alternative ports, nor does it provide the ability to distribute mail delivery across a set of equal-priority mail servers .

• The MX mechanism provides the ability to run multiple mail servers for a single domain, and allows the specification of an order in which they should be tried.