Reverse DNS Lookup

A PTR (Pointer) record maps an IP address to a domain name. PTR records are stored in the reverse DNS zone and are used by mail servers to verify the identity of sending servers, network diagnostics, and system logging. For example, the IP 8.8.8.8 resolves to dns.google via a PTR record.

Not all IP addresses have PTR records configured. PTR records must be set up by the IP block owner (typically an ISP or hosting provider). Consumer IP addresses often don't have PTR records. Servers and mail servers usually do — mail servers without valid reverse DNS are often flagged as spam.

Forward-confirmed reverse DNS (FCrDNS) is when the hostname resolved via PTR record also resolves back to the same IP via an A record. For example: 8.8.8.8 → dns.google → 8.8.8.8. This confirmation is used by email servers to verify that a server's IP and hostname are consistent, which is a strong spam prevention signal.

Email servers often check the reverse DNS of the connecting server's IP. If the PTR record doesn't exist or doesn't match the sending domain, the email is more likely to be flagged as spam. For email deliverability, it's important that your mail server's IP has a PTR record pointing to a hostname that resolves back to that same IP (FCrDNS).

Yes. This tool supports both IPv4 and IPv6 reverse DNS lookups. For IPv6, the lookup queries the ip6.arpa zone instead of in-addr.arpa. For example, the IPv6 address 2001:4860:4860::8888 (one of Google's DNS servers) resolves to dns.google. IPv6 PTR records are less commonly configured than IPv4 ones.