Reverse DNS (PTR) lookup

Turn an IP address back into a hostname, and check that the hostname resolves back to the IP — forward-confirmed reverse DNS, the reverse-DNS test that mail servers use to judge a sending IP.

Verbose outputResolves the PTR record and forward-confirms it (FCrDNS) — what mail servers check.

Why reverse DNS matters

Every IP address can have a PTR record that maps it back to a hostname. It is the mirror image of the usual A/AAAA lookup. Mail servers lean on it heavily: an IP that sends mail but has no PTR record — or whose PTR hostname does not resolve back to the same IP — is widely treated as suspicious and is a common reason legitimate mail lands in spam or is rejected outright.

Forward-confirmed reverse DNS (FCrDNS)

FCrDNS is the two-step check this tool runs: resolve the IP's PTR record to a hostname, then resolve that hostname's A/AAAA record and confirm it contains the original IP. When both agree, the reverse DNS is forward-confirmed and trusted. If you run a mail server, make sure your sending IPs pass this — your hosting provider usually sets the PTR record, not your DNS provider.

Checking a domain's records instead of an IP? Use the DNS lookup tool, or the email DNS validator for SPF, DKIM and DMARC.