Reverse DNS (PTR) Checker

What is a PTR / reverse DNS record?

A PTR record maps an IP address back to a hostname — the reverse of the A/AAAA record that maps a hostname to an IP. For email, the PTR of your sending IP is your server’s public identity: receivers reverse-resolve the connecting IP before they accept the message.

An IP with no PTR, or with a generic ISP-assigned name like host-203-0-113-5.example-isp.net, is treated as a likely source of spam. A clean, dedicated hostname that matches your mail domain signals a legitimate sender.

Forward-confirmed reverse DNS (FCrDNS)

Best practice is forward-confirmed reverse DNS: the PTR hostname must itself resolve forward (via A/AAAA) back to the original IP. This two-way match proves the operator controls both the IP and the hostname, and several large providers require it before they will accept mail.

This checker performs both directions: it reverse-resolves the IP to its PTR hostname(s), then forward-resolves each hostname and confirms the original IP is in the answer.

How this checker works

We accept an IPv4 or IPv6 address, query its PTR records, and then look up the A/AAAA records of each returned hostname to verify forward-confirmation. We report the hostnames found, whether FCrDNS passes, and flag a missing PTR or a forward/reverse mismatch.

Frequently asked questions

Why does PTR matter for email deliverability?

Receiving mail servers reverse-resolve the connecting IP as a basic spam signal. No PTR, a generic PTR, or one that fails forward-confirmation commonly results in rejection (often a 5xx error mentioning rDNS) or routing straight to spam — regardless of how good your SPF, DKIM, and DMARC are.

Who sets the PTR record?

The owner of the IP block does — usually your hosting provider, ISP, or cloud platform — not your domain’s DNS. To set or change a PTR you open a request with whoever assigned you the IP. Your own authoritative DNS only controls the forward (A/AAAA) side needed for FCrDNS.

Is a generic PTR really a problem?

For bulk or transactional sending, yes. A default ISP-style PTR marks the IP as a generic endpoint rather than a managed mail server, and some providers penalize it. Use a dedicated hostname (e.g. mail.yourdomain.com) that forward-resolves back to the IP.

Does this work for IPv6?

Yes. IPv6 PTR records live under ip6.arpa and matter just as much — several providers are stricter about reverse DNS on IPv6 than on IPv4. Paste an IPv6 address and the checker reverse-resolves it and forward-confirms the AAAA records the same way.