A PTR record maps an IP address back to a hostname via reverse DNS lookup. It's the inverse of an A record: instead of name→IP, it's IP→name.
Why this matters: mail servers check PTR records to verify sender legitimacy. If your mail server's IP has no PTR or a mismatched one, your email lands in spam. Same for reputation systems and abuse investigations—your IP's reverse DNS is part of your digital fingerprint.
Technically, PTR records live in special reverse zones (in-addr.arpa for IPv4, ip6.arpa for IPv6) and are usually managed by your hosting provider or ISP, not your registrar. You can't just set one from your domain's DNS control panel.
For bulletproof operators: a clean PTR record actually helps you blend in. Bad actors often run mail servers with broken reverse DNS. If you're running a legitimate mail server on offshore hosting, a proper PTR—matching your A record—signals competence to mail filters. If you're hiding, reverse DNS consistency is just another box to tick.