How do I set a PTR record for my server?

You cannot set it in your own DNS. The reverse zone is delegated with the address block, so the PTR is set by whoever holds the block, which is your hosting provider or ISP. Most providers offer a field for it in their control panel or accept a support request. Set the forward record first so the check passes immediately.

Why does my mail get rejected for missing reverse DNS?

Receivers use rDNS as a cheap sender-legitimacy signal, since setting one requires control of the address block, which spammers on hijacked hosts usually lack. Publish a PTR that names your mail host, and make sure that host resolves forward to the same address. Residential connections generally cannot pass this and should relay through a provider instead.

What is forward-confirmed reverse DNS?

The full round trip. Take the address, find the PTR name, resolve that name, and confirm the original address is among the results. It closes the gap that a PTR alone leaves, because a PTR is set by the address holder and can claim any name, including one they do not control.

Does reverse DNS work for IPv6?

Yes, through the ip6.arpa zone, with each nibble of the address as a separate label in reverse order. That makes 32 labels for a full IPv6 address. Because IPv6 hosts often use privacy addresses that change daily, operators frequently publish wildcard PTRs or none at all.

Is reverse DNS the same as finding all domains hosted on an IP?

No, and that is a common confusion. A PTR is one name set by the address holder. Finding every domain that points at an address requires a forward-DNS dataset built by scanning, which is a different product entirely and is not what this tool does.

Reverse DNS Lookup

Find the PTR record for any IPv4 or IPv6 address and run the forward-confirmed check that mail servers apply.

No PTR216.73.216.7

The operator publishes no PTR record for this address. Mail servers frequently refuse mail from such addresses outright.

What the resolvers returned

Your address

Address: 216.73.216.7
Reverse name: 7.216.73.216.in-addr.arpa
PTR records: None
Forward lookup: The PTR name resolves to nothing
Response code: NXDOMAIN

Why forward confirmation matters

FCrDNS

A PTR record is a claim by whoever controls the address block. Anyone with a /24 can point it at mail.google.com. Forward-confirmed reverse DNS closes that hole: take the PTR name, resolve it forward, and check the answer contains the address you started from. Only then do both halves of the pair agree, and only then does the name prove anything.

Mail servers lean on this because it is cheap and it proves control of both the address block and the name. Postfix calls the result unknown when it fails, and many operators score or reject on that. Sending servers on a residential connection almost never pass, which is one reason mail from home is treated with suspicion.

Same answer as JSON: /api/v1/reverse/216.73.216.7

How the query is built

For IPv4, the four octets are reversed and appended to in-addr.arpa, so 203.0.113.45 becomes 45.113.0.203.in-addr.arpa. For IPv6 the address is expanded to its full 32 hexadecimal digits, each digit becomes a label, the order is reversed, and ip6.arpa is appended. The tool shows the constructed query name so you can reuse it with dig.

Why the forward check matters

A PTR record is published by whoever controls the reverse zone, which is the address holder. Nothing stops them naming the address mail.your-bank.example. The forward lookup is what makes that claim checkable: unless they also control your-bank.example, the forward record will not point back. Software that trusts the PTR alone has been fooled this way for decades, which is why the forward-confirmed variant became the operational standard.

Limits

We query public recursive resolvers, so a very recent change may still be cached. Reverse delegation for small allocations often uses the RFC 2317 classless delegation pattern, which introduces an extra CNAME hop; the tool follows it and shows the chain.

About this tool

Enter an address and we query the PTR record in the in-addr.arpa or ip6.arpa zone, then resolve that hostname forward and check whether it points back to the address you started from. That round trip is forward-confirmed reverse DNS, and it is what mail servers and SSH daemons check rather than the PTR alone. Only the operator holding the address block can publish a PTR, which is why the check carries weight.

How to read the result

PTR record: The name the network that owns the address published for it, in in-addr.arpa for IPv4 or ip6.arpa for IPv6. Those zones are delegated along with the address allocation, so only the operator can set one, and many addresses have none at all.
Forward-confirmed result: We resolve the PTR hostname to A and AAAA records and check whether the original address appears. Pass means the two directions agree, and fail means the PTR names a host that does not claim the address, which mail servers commonly treat as a spam signal.
No PTR found: The operator publishes no PTR for this address, or the reverse zone is not delegated. For a mail server that is a deliverability problem, and for a home connection it means nothing.
Generic PTR pattern: A PTR built out of the address itself, such as a dotted or dashed form plus the ISP domain. It marks the address as dynamic residential space or as unconfigured datacenter space, and many mail receivers score those patterns down even when the forward check passes.
Multiple PTR records: RFC 1035 permits more than one name, but operational practice discourages it, because consumers pick one arbitrarily and the behaviour becomes unpredictable. For a mail server, publish exactly one.

Questions people ask

How do I set a PTR record for my server?: You cannot set it in your own DNS. The reverse zone is delegated with the address block, so the PTR is set by whoever holds the block, which is your hosting provider or ISP. Most providers offer a field for it in their control panel or accept a support request. Set the forward record first so the check passes immediately.
Why does my mail get rejected for missing reverse DNS?: Receivers use rDNS as a cheap sender-legitimacy signal, since setting one requires control of the address block, which spammers on hijacked hosts usually lack. Publish a PTR that names your mail host, and make sure that host resolves forward to the same address. Residential connections generally cannot pass this and should relay through a provider instead.
What is forward-confirmed reverse DNS?: The full round trip. Take the address, find the PTR name, resolve that name, and confirm the original address is among the results. It closes the gap that a PTR alone leaves, because a PTR is set by the address holder and can claim any name, including one they do not control.
Does reverse DNS work for IPv6?: Yes, through the ip6.arpa zone, with each nibble of the address as a separate label in reverse order. That makes 32 labels for a full IPv6 address. Because IPv6 hosts often use privacy addresses that change daily, operators frequently publish wildcard PTRs or none at all.
Is reverse DNS the same as finding all domains hosted on an IP?: No, and that is a common confusion. A PTR is one name set by the address holder. Finding every domain that points at an address requires a forward-DNS dataset built by scanning, which is a different product entirely and is not what this tool does.

Last reviewed 2026-09-05.