PTR record

8.8.8.8.in-addr.arpa. 75991 IN PTR dns.google.
  ; points to dns.google

1.1.1.1.in-addr.arpa. 651 IN PTR one.one.one.one.
  ; points to one.one.one.one

9.9.9.9.in-addr.arpa. 164172 IN PTR dns9.quad9.net.
  ; points to dns9.quad9.net

What the PTR record does

For 192.0.2.25 the PTR lives at 25.2.0.192.in-addr.arpa. For IPv6, each of the 32 hex nibbles becomes a label, in reverse. Reverse zones belong to whoever holds the address block, usually your hosting provider or ISP, so PTRs are set in their control panel, not in your domain's zone.

Mail receivers check that a sending IP has a PTR and that the name resolves back to the same IP ("forward-confirmed reverse DNS"). Gmail's bulk-sender guidelines require it. Most other software only uses PTRs to show friendlier names in logs and traceroutes.

Zone-file syntax

25.2.0.192.in-addr.arpa.  3600  IN  PTR  mail.example.com.

Wire format: RDATA is one domain name.

Fields

Field	Meaning
Owner	Reversed address under in-addr.arpa. or ip6.arpa.
Target	The hostname. It should have an A/AAAA record pointing back to the same address.

Common mistakes

• Trying to add a PTR in your domain's DNS zone; it must be set by the owner of the IP block.
• A generic PTR like ip-192-0-2-25.provider.net on a mail server; many receivers score that as residential or dynamic.
• A PTR name that does not resolve back to the IP.

Specification

• RFC 1035: Domain names - implementation and specification
• RFC 3596: DNS Extensions to Support IP Version 6
• RFC 2317: Classless IN-ADDR.ARPA delegation

Related record types

• A: map a hostname to an IPv4 address
• AAAA: map a hostname to an IPv6 address
• MX: where email for a domain is delivered

All DNS record types