What is a reverse DNS lookup?

A reverse DNS lookup queries a PTR record to map an IP address back to a hostname. Unlike a forward DNS lookup (hostname to IP), reverse lookups start from the IP address formatted as a special DNS name — for IPv4, the octets are reversed and .in-addr.arpa is appended (e.g. 8.8.8.8 becomes 8.8.8.8.in-addr.arpa).

Why does reverse DNS matter for email?

Most mail servers check that the sending IP has a PTR record matching its forward DNS (A record). A missing or mismatched PTR record is a strong spam signal that causes many servers to reject or junk your emails. Ensuring PTR records are set correctly is a critical step in email deliverability.

What does "No PTR record found" mean?

It means the IP address does not have a PTR record configured in its reverse DNS zone. The reverse DNS zone is managed by the IP address owner (your ISP or hosting provider), not your domain registrar. You must contact them or use your hosting panel to set a PTR record.

How is IPv6 reverse DNS different?

For IPv6, each nibble (hex digit) of the full expanded address is reversed and separated by dots, then .ip6.arpa is appended. For example, 2001:db8::1 expands to 2001:0db8:0000:0000:0000:0000:0000:0001, then becomes 1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.

Can a single IP have multiple PTR records?

Technically yes, but it is strongly discouraged. Multiple PTR records cause inconsistent results depending on which answer a resolver returns first. Best practice is to have exactly one PTR record per IP address, and ensure it matches the forward A record for that hostname.

Why does this tool use DNS-over-HTTPS?

Browsers cannot make raw UDP DNS queries directly. DNS-over-HTTPS (DoH) sends the DNS query as an HTTPS request to a public resolver, allowing fully client-side lookups without any server-side proxy. This tool uses Cloudflare's public DoH endpoint at cloudflare-dns.com.

Reverse DNS Lookup

Enter an IPv4 or IPv6 address to instantly resolve its PTR record hostname via Cloudflare DNS-over-HTTPS.

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Enter an IP address to resolve its hostname

Supports IPv4 and IPv6

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Summary

The Reverse DNS Lookup tool resolves any IPv4 or IPv6 address to its associated hostname by querying a PTR record via Cloudflare's public DNS-over-HTTPS API. No software installation is needed — all lookups run directly in your browser. Results include the full PTR record name, returned hostname, and response time so you can diagnose mail server configuration, verify hosting providers, and investigate unfamiliar IP addresses in seconds.

How it works

Enter an IPv4 address (e.g. 8.8.8.8) or IPv6 address in the input field.
The tool formats the address as a PTR query name (reversed octets + .in-addr.arpa for IPv4).
A DNS-over-HTTPS request is sent to Cloudflare's public resolver (no API key needed).
The PTR record answer is parsed and the resolved hostname is displayed.
Response time, raw PTR name, and TTL are shown alongside the hostname.

Use cases

Verify that a mail server IP has a matching PTR record for email deliverability.
Identify the hosting provider or ISP behind an IP address.
Investigate unfamiliar IP addresses found in server logs.
Confirm that forward and reverse DNS are consistent for a domain.
Troubleshoot failed reverse DNS lookups in your own infrastructure.
Check PTR records before sending bulk email from a new IP.
Audit server IPs to ensure hostnames match expected values.
Quickly perform rDNS checks without a terminal or dig installed.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu