PTR record (pointer record) is the reverse of an A/AAAA record. Instead of hostname → IP, it maps IP → hostname. Reverse DNS lives under .in-addr.arpa (IPv4) and .ip6.arpa (IPv6).
Record Format
229.132.16.104.in-addr.arpa. PTR example.com.Who Controls PTR
PTR records are set by whoever owns the IP block — usually the hosting provider or ISP, not the domain owner. To change PTR, you file a request with your provider (AWS, GCP, Linode, etc.).
Email Impact
Receiving mail servers reject or heavily penalise inbound mail from a sending IP with no PTR, or one whose PTR doesn’t forward-confirm (FCrDNS). Setting up outbound mail without PTR = every message going to spam.
FCrDNS
Forward-Confirmed Reverse DNS: the PTR of an IP resolves to a hostname, and the A record of that hostname resolves back to the same IP. Required by most large mail providers.
Related
Check the A record glossary entry, read what a blacklist actually is, and browse every major DNS record type.