Reverse DNS Lookup
Find the host name behind IP addresses. Paste up to twenty public IPv4 or IPv6 addresses and get the PTR name of each, then a forward-confirmation check: the name is resolved again to see whether it points back to the same address. That check, known as FCrDNS, is what mail servers use to judge senders.
- Encrypted connection
- No sign-up
- Free to use
Up to 20 public IPv4 or IPv6 addresses, one per line. Private and reserved addresses are not looked up.
| IP address | Reverse name (PTR) | Forward-confirmed |
|---|
How to use Reverse DNS Lookup
- Paste up to 20 public IP addresses.
- Select Look up.
- Read the PTR name of each address.
- Check whether each is forward-confirmed.
Reverse DNS Lookup features
Bulk lookup
Up to 20 addresses per request.
IPv4 and IPv6
Both address families.
Forward confirmation
Checks the PTR name resolves back to the address.
Mail-server relevance
FCrDNS is required by many receiving mail servers.
Safe
Private and reserved addresses are refused.
Clear results
Missing PTR records and mismatches explained.
When to use Reverse DNS Lookup
- Checking the reverse DNS of a mail server.
- Identifying hosts in firewall or server logs.
- Verifying a hosting provider configured PTR records.
- Investigating unknown connections.
Reverse DNS Lookup FAQ
What is reverse DNS?
The mapping from an IP address back to a host name, stored as a PTR record in a special domain (in-addr.arpa or ip6.arpa) controlled by whoever owns the address block.
What is forward-confirmed reverse DNS?
When the PTR name of an address resolves back to the same address. It shows that the owner of the address and the owner of the name agree, which mail servers use as a trust signal.
Why does my server have no PTR record?
PTR records are set by the owner of the IP block, usually your hosting or internet provider, not in your own domain’s DNS. Ask them to set it.
Can I look up private addresses?
No. Private and reserved addresses have no public reverse DNS, and looking them up could reveal internal network details.
How is this different from the DNS Lookup tool?
DNS Lookup handles one address or name at a time with all record types. This tool checks many addresses at once and adds forward confirmation.
What is sent?
Only the IP addresses, which the server looks up in public DNS.
From address to name and back
Forward DNS turns names into addresses; reverse DNS does the opposite. Each IP address can have a PTR record giving a host name, kept in a special part of the DNS tree that is delegated to whoever owns the address block. That is why you set it with your hosting provider rather than in your domain settings.
A PTR name on its own proves little, because the owner of an address can claim any name. Forward confirmation closes the gap: look up the PTR name, resolve it to addresses, and check that the original address is among them. Only when both directions agree do the owners of the address and of the name support each other.
Mail delivery depends on this. Many receiving servers reject or mark as spam any message from a server without forward-confirmed reverse DNS, and providers such as Gmail list it as a requirement for bulk senders. Checking your outgoing mail servers here is a quick health check.
Reverse DNS is also useful in investigations, turning addresses in logs into recognisable names. Treat the names as hints rather than proof of identity, since only forward-confirmed names are corroborated.