PTR record
The reverse-DNS record. Maps an IP address back to a hostname. Used by mail servers, logs, and security scanners.
A PTR (pointer) record is the inverse of an A or AAAA record. Where A records say example.com → 198.51.100.42, PTR records say 198.51.100.42 → example.com.
42.100.51.198.in-addr.arpa. PTR mail.example.com.
Reverse-DNS records live in special domains (in-addr.arpa for IPv4, ip6.arpa for IPv6) with the IP octets written in reverse order. You don't usually edit this directly.
Where PTR records actually matter
Email deliverability. Receiving mail servers do a reverse-DNS lookup on the sending IP. If the PTR doesn't exist, or doesn't match the EHLO/HELO domain claimed by the sender, the receiver may reject the mail or flag it as spam.
If you run your own mail server, you need a PTR record on its outbound IP that matches its hostname. This is configured with your IP provider (the company that owns the IP block), not with your DNS host. If you use a transactional ESP (SendGrid, Postmark, Resend), they handle it.
Server logs. When a web server logs an inbound IP, some configurations resolve it to a hostname via PTR. Useful for analytics or threat detection, slow if abused.
Security scanners. Tools like Shodan use reverse DNS to associate IPs with services. Your PTR is part of your public footprint whether you like it or not.
What you don't use it for
PTR records are not how browsers find your site. They're a separate mapping, used by specific tools for specific reasons. Most SaaS engineers never directly create or edit one.