Reverse DNS (rDNS) resolves an IP address to a hostname, opposite to the standard A record or AAAA record lookup. It uses PTR (Pointer) records instead of address records.
For IPv4, reverse DNS queries the special domain in-addr.arpa, with octets reversed. For example, 192.0.2.5 becomes 5.2.0.192.in-addr.arpa. IPv6 uses ip6.arpa with the address expressed as reversed nibbles (hex digits).
Unlike forward DNS, reverse zone authority is delegated by the Regional Internet Registry or ISP that owns the IP block, since IP address space (not domain names) is being delegated. This is why you cannot set up reverse DNS yourself—your hosting provider or ISP must create the PTR record.
Common use case: Mail servers check reverse DNS to verify sender legitimacy. Many reject mail from servers with missing or mismatched PTR records. This forward-confirmed reverse DNS (FCrDNS) check—where the PTR target, when looked up forward, resolves back to the original IP—is critical for email deliverability. Misconfigured or ISP-assigned generic PTR values often trigger spam filters.
Example: A mail server at mail.example.com (IP 93.184.216.34) should have a PTR record on 34.216.184.93.in-addr.arpa pointing back to mail.example.com. When that hostname is looked up, it should resolve to 93.184.216.34 again.
TipReverse DNS (the PTR record) is controlled by whoever owns the IP address — usually your host or ISP, not your DNS provider. Matching forward and reverse records helps email delivery.