Reverse DNS
Resolve an IP address to its hostname via PTR record, with forward-confirmed check.
About Reverse DNS
Takes an IP address and resolves it back to its hostname via the PTR record, the reverse of a normal DNS lookup. This matters most for mail servers — most receiving mail systems check that a sending IP has a valid, matching PTR record before accepting a connection, and a missing or mismatched one is a common, silent cause of mail getting rejected or flagged as spam. If a PTR lookup returns nothing, that's itself diagnostic information — it usually means the hosting provider hasn't set one up.
Some mail systems go a step further and check that the PTR hostname's own forward A record resolves back to the original IP (forward-confirmed reverse DNS) — having a PTR record at all isn't automatically sufficient if that round-trip doesn't match.