Which DNS record is used to identify the mail exchangers for a domain?

• A. A
• B. MX
• C. NS
• D. CNAME

Answer: (B)

The capability to route email for a domain relies on a specific DNS record that identifies where mail should be delivered. That record type is the MX (Mail Exchange) record. An MX record lists one or more mail servers by hostname, each with a priority value so senders know which server to try first. When another domain wants to deliver mail to someone at this domain, its mail transfer agent looks up the domain’s MX records and connects to the server with the highest priority (lowest number). If that server can’t be reached, it moves to the next one in order of priority. The hostname listed in an MX record should have its own A (IPv4) or AAAA (IPv6) record so the sender can actually reach it.

Other common DNS record types serve different purposes: an A record maps a domain to an IP address, NS records indicate which DNS servers authority for the domain, and a CNAME record is an alias from one name to another. These do not specify mail exchangers, which is why the MX record is the correct choice for identifying where to deliver domain email.