Which of the following types of DNS records enables support for email?

An A record maps a hostname to an IPv4 address and has no direct role in email routing or mail server identification.

An MX record specifies the hostname of the mail server that handles incoming email for a domain, and its associated priority value enables failover when multiple mail servers are configured. Without a correctly configured MX record, external systems have no way to determine where to deliver email for the domain. MX records are a required DNS record type for any domain intended to receive email.

A PTR record is used for reverse DNS lookups, mapping an IP address back to a hostname, and plays no part in directing inbound email traffic.

An AAAA record maps a hostname to an IPv6 address and, like the A record, serves address resolution purposes rather than email delivery routing.