Glossary · DNS

PTR Record (Reverse DNS)

A PTR record maps an IP address back to a hostname in the in-addr.arpa or ip6.arpa tree, and mail servers often check it.

Updated October 5, 2026

A PTR (pointer) record maps an IP address to a hostname, the reverse of an A record. It lives in a special zone: in-addr.arpa for IPv4 and ip6.arpa for IPv6.

Why it matters

Many receiving mail servers look up the PTR record of the connecting IP and reject or penalize mail from addresses with no reverse DNS, or with a name that does not resolve back to the same IP (forward-confirmed reverse DNS). Logs and diagnostic tools also use PTR to show readable names.

Whoever owns the IP address controls its PTR record. That is usually your hosting provider or ISP, not your domain's DNS host.

Example

For the address 203.0.113.10, the octets are reversed:

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

Test with dig -x 203.0.113.10 +short. For good mail reputation, mail.example.com should have an A record pointing back to 203.0.113.10, and your SMTP greeting (HELO) should use that name.

Common mistakes

  • Adding the PTR record in your domain's DNS panel. It must be set by the owner of the IP block.
  • Using a generic provider name such as an auto-generated host string for a mail server.
  • Having a PTR that does not resolve forward to the same IP.
  • Forgetting IPv6, where the PTR name is built from the address reversed one hex digit at a time.

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