What is a PTR record?

A PTR record maps an IP address back to a hostname, the reverse of the usual A/AAAA direction. It lives in the special zones in-addr.arpa (IPv4) and ip6.arpa (IPv6), which are delegated to whoever controls the IP block, usually your ISP or hosting provider.

What is forward-confirmed reverse DNS (FCrDNS)?

The two-way check: the IP's PTR record gives a hostname, and that hostname must resolve back to the same IP. Mail servers rely on it heavily; an outbound SMTP server without matching FCrDNS gets rejected or scored as spam by most large receivers.

How do I change the PTR record of my IP?

You cannot set it in your own DNS zone. The reverse zone belongs to the owner of the IP block, so you request the PTR from your ISP or set it in your hosting/cloud provider's panel (most VPS providers expose a reverse-DNS field per IP).

Reverse DNS Lookup

IPv4 or IPv6 address

Examples:

What a reverse DNS lookup shows

Normal DNS answers "which IP belongs to this name". Reverse DNS answers the opposite: the PTR record of an address, stored under in-addr.arpa (IPv4) or ip6.arpa (IPv6) with the address bytes reversed. This tool shows the exact .arpa name being queried, every PTR hostname it returns, and then performs the forward confirmation: it resolves each hostname back and checks whether it points at the original IP.

That round trip, forward-confirmed reverse DNS (FCrDNS), is what mail servers check before accepting SMTP connections; a sending IP whose PTR is missing or does not confirm gets rejected or heavily penalised by Gmail, Microsoft and most filters. Beyond mail, the PTR hostname usually reveals the network operator and often the city or exchange the address terminates at, which makes it a standard first step when reading server logs or a traceroute.

For the full picture of an address (owner, ASN, geolocation, blacklist status alongside its rDNS), open it in the IP lookup.