Reverse DNS
Lookup that finds the domain name associated with an IP address using PTR records.
Reverse DNS (rDNS) finds the domain name associated with an IP address by looking up the corresponding PTR record in DNS. It is the mirror image of a normal forward lookup.
A forward DNS lookup answers the question "which IP address belongs to this domain name?" by querying records such as A or AAAA. A reverse DNS lookup answers the opposite question — "which domain name is registered for this IP address?" — by querying PTR records in the in-addr.arpa and ip6.arpa zones.
Reverse DNS is widely used in email systems, server logging, network diagnostics, security tooling and reputation systems. Logs become more readable when raw IPs resolve to recognisable hostnames, and security tools use rDNS as one signal when classifying connections.
In the email ecosystem, reverse DNS is evaluated alongside MX records, SPF, DKIM and DMARC to confirm that a sending mail server is who it claims to be. A consistent forward, reverse and HELO identity is one of the baseline expectations for legitimate mail infrastructure.