Mail Exchange Record

Mail Exchange Record is often noted as an MX record, and is a resource record located in the domain name system (DNS). This record specifies that a mail server is responsible for accepting the recipient’s email communication, and specifies how email should be routed using the Simple Mail Transfer Protocol (SMTP). The MX mechanism allows a single domain to run multiple mail servers and allows administrators to specify in which order the network should try these servers.

These records collect relatively simple information. When an email message is sent via the internet, the sender’s mail transfer agent will send a query to the DNS of the MX records for each recipient’s domain name.  The DNS will answer this query with a list of mail exchange servers’ host names that accept incoming mail for that domain and their preferences.  Once it has access to this information, the sending agent will attempt to establish SMTP for the same domain.

Spammers often attempt to leverage MX servers to target email users. These senders can attempt to connect to backup MX servers to avoid anti-spam filters that may be running on the primary mail exchange server.  While possible, many servers can leverage security techniques, including bogus backup or back end servers, to prevent spammers from accessing their information.