Reverse DNS (PTR) Lookup
Enter any IPv4 or IPv6 address to see its reverse DNS — the hostname the IP points back to — and the exact reverse-DNS name you'd publish a PTR record at (in-addr.arpa for IPv4, ip6.arpa for IPv6). Reverse DNS matters most for mail servers, where receivers check that a sending IP has a valid PTR matching its forward hostname.
Reviewed by the SysGlass team · Updated July 21, 2026
What it checks
- The PTR record(s) an IP resolves to (its reverse hostname)
- The generated reverse-DNS name for IPv4: octets reversed + in-addr.arpa
- The generated reverse-DNS name for IPv6: nibbles reversed + ip6.arpa
- Whether the IP has any reverse DNS at all
- Works for both IPv4 and IPv6 addresses
How to read the result
- OK means the IP has a PTR record; the summary shows the hostname it resolves to.
- 'No PTR record' is normal for client IPs but a problem for mail servers — receivers may reject or distrust mail from an IP with no matching PTR.
- The 'Reverse name' row is the exact DNS name to create the PTR record at (e.g. 8.8.8.8 -> 8.8.8.8.in-addr.arpa).
- For good deliverability, the PTR hostname and its forward A/AAAA record should match (forward-confirmed reverse DNS).
Frequently asked questions
What is a PTR record / reverse DNS?
A PTR record maps an IP address back to a hostname — the reverse of an A or AAAA record. It's published under the special in-addr.arpa (IPv4) or ip6.arpa (IPv6) zones.
How do I generate the reverse DNS name for an IP?
For IPv4, reverse the four octets and append .in-addr.arpa (1.2.3.4 -> 4.3.2.1.in-addr.arpa). For IPv6, expand the address, reverse every nibble, and append .ip6.arpa. This tool shows that name for you.
Why does my mail get rejected for missing reverse DNS?
Many mail servers require a sending IP to have a PTR record, ideally one matching the server's forward hostname. A missing or mismatched PTR is a common cause of mail being deferred or rejected.
Who sets the PTR record?
The owner of the IP block — usually your hosting provider or ISP — controls reverse DNS, not your domain's DNS. Ask them to set the PTR at the reverse name shown here.
Does it support IPv6 reverse DNS?
Yes. Enter an IPv6 address and the tool shows both the ip6.arpa reverse name and any PTR record published for it.