Reverse Lookup (PTR)
Reverse-resolve an IP address to a hostname.
Enter a value above to run Reverse Lookup (PTR)
e.g. 1.1.1.1
Quick answer
A reverse (PTR) lookup finds the hostname that an IP address maps back to, the opposite of a normal A/AAAA lookup. It is commonly used to verify mail servers, since many providers reject email from IPs without a matching PTR record.
A reverse lookup (PTR) resolves an IP address back to a hostname, the opposite of a normal A/AAAA lookup. Instead of asking "what IP does example.com use?", you ask "what name is registered for 203.0.113.10?". Reverse records live under the special in-addr.arpa (IPv4) and ip6.arpa (IPv6) zones, and they are controlled by whoever owns the IP block, not the domain. This tool is essential when you send email: many mail servers reject or spam-flag messages from IPs that lack a matching PTR record.
How it works
The resolver reverses the IP and appends the ARPA suffix. For 203.0.113.10 it queries 10.113.0.203.in-addr.arpa; for IPv6 it expands the address into reversed nibbles under ip6.arpa. It then asks for the PTR record, which returns the hostname the IP owner assigned. Because reverse zones are delegated by the ISP or hosting provider that holds the IP range, you cannot set a PTR from your own domain's DNS panel.
How to read the results
A successful lookup returns one hostname, such as mail.example.com. Compare it to the forward record: a mail server checks that the PTR name also resolves back to the same IP (forward-confirmed reverse DNS, or FCrDNS). If the query returns NXDOMAIN or no answer, that IP has no PTR set. A generic-looking name from the provider (like static-203-0-113-10.isp.net) works technically but looks less trustworthy to receiving servers.
Why it matters
PTR records are a core signal for email deliverability. Postfix, Exchange, and most large providers reject or heavily penalise mail from IPs with a missing PTR or one that does not forward-confirm. Reverse DNS also makes server logs, traceroutes, and abuse reports readable, and some SSH and firewall setups log the resolved name. For any host that sends mail directly, a matching PTR is not optional.
Frequently asked questions
- Why does my PTR lookup return nothing?
- Most likely no PTR record exists for that IP. Reverse zones are managed by the party that owns the IP block, so you must request the record from your hosting provider or ISP, not set it in your own domain's DNS. Freshly provisioned servers and residential connections often ship with no PTR at all.
- How do I set a PTR record for my server?
- Open your hosting or cloud provider's control panel (AWS, DigitalOcean, Hetzner, etc.) and look for a "reverse DNS" or "PTR" field tied to the IP. Set it to a hostname you control, then create a matching forward A/AAAA record so the two confirm each other. On dedicated ranges you may instead delegate the reverse zone.
- Can one IP address have multiple PTR records?
- Technically yes, an IP can have several PTR entries, but it is discouraged. Many mail servers and validation tools only read the first answer, so extra records can cause inconsistent results and failed FCrDNS checks. Best practice is exactly one PTR per IP, pointing to the primary hostname that also resolves forward to that same address.