What is the primary purpose of MX records?

• A. They specify mail servers responsible for receiving email for the domain.
• B. They map domain names to IP addresses.
• C. They indicate reverse DNS mappings for the domain.
• D. They designate the authoritative DNS server for the domain.

Answer: (A)

MX records specify the mail servers that receive email for a domain. They list the hostnames of the mail exchangers and include a priority value to indicate which server should be tried first. When an email is sent to an address at that domain, the sending mail transfer agent looks up the domain’s MX records to find the destination mail server and then delivers the message via SMTP. The lower priority number means higher preference, so if the primary server can’t be reached, delivery can be attempted to the next one in order.

This is distinct from other DNS records: A or AAAA records map domain names to IP addresses, PTR records provide reverse DNS mappings from IP addresses back to domain names, and NS records designate the authoritative DNS servers for the domain. An MX record must point to a host name that has its own reachable A or AAAA record so the mail server can actually be reached.