What a PTR record is
A PTR record, short for Pointer record, does the opposite of an A record. Where an A record maps a name to an IP address, a PTR record maps an IP address back to a name. This is the basis of reverse DNS, which answers the question of what hostname is associated with a given address.
How it works
Reverse lookups use a special DNS zone built from the address itself:
- IPv4 addresses are queried under the
in-addr.arpadomain, with the octets reversed. - IPv6 addresses use the
ip6.arpadomain in a similar reversed form. - The PTR record there returns the associated hostname.
The owner of the IP range, usually the internet provider or hosting company, controls these records, not the domain owner.
Why it matters
Reverse DNS is heavily used in email. Many receiving mail servers check whether a sending server's IP has a matching PTR record and whether that name lines up with its forward A record, a check known as forward-confirmed reverse DNS. A missing or mismatched PTR can cause legitimate mail to be flagged as spam. PTR records also help with logging, diagnostics, and tracing traffic. For example, an IP like 203.0.113.10 might resolve back to mail.example.com. You can perform reverse lookups with the WhatIP reverse-ip tool.