DNS contains different record types that serve specific purposes. To determine where incoming email should be delivered for a particular domain, DNS uses an MX (Mail Exchange) record. CompTIA A+ identifies MX records as essential for routing mail from external senders to the appropriate mail server assigned to a domain.
The MX record specifies:
The mail server hostname responsible for receiving messages
Priority values, which determine which server to try first
The server destination for SMTP traffic
When someone sends an email, the sending mail server queries DNS to find the MX record for the recipient’s domain. The SMTP server then relays the email to the server listed in that record.
CNAME is used for aliasing hostnames, TXT is used for verification/security (SPF, DKIM), and AAAA maps a hostname to an IPv6 address. None of these direct email delivery. Only MX records are designed to instruct mail servers where to deliver incoming email.
Thus, the correct answer is MX.
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