Reverse DNS maps an IP address back to a hostname. Normal DNS goes from domain to IP; reverse DNS goes from IP to domain. It works by querying PTR records in the .in-addr.arpa (IPv4) or .ip6.arpa (IPv6) zones.

What is a PTR record?

A PTR (pointer) record is the DNS record type used for reverse DNS lookups. It maps an IP address to a hostname. PTR records are stored in reverse DNS zones managed by the IP address owner, usually a hosting provider or ISP.

Why does reverse DNS matter for email?

Mail servers check the PTR record of the sending IP before accepting messages. No PTR record, or a PTR that does not match the sending server's hostname, signals that the sender may be a spammer. Gmail, Microsoft, and most major providers run this check. Failing it can lead to rejected messages or spam folder placement.

What is FCrDNS (Forward-Confirmed reverse DNS)?

FCrDNS checks that the forward and reverse DNS paths agree. First, the PTR record for an IP is looked up to get a hostname. Then, the A record for that hostname is looked up to get an IP. If the IPs match, FCrDNS passes. If they do not match, the check fails. Gmail and Microsoft both perform this verification on incoming mail.

How do I set up reverse DNS for my server?

It depends on your hosting provider. On AWS, Azure, and GCP, you can set PTR records through the cloud console or by submitting a support request. On dedicated servers or VPS, your hosting provider usually has a control panel option for it. Contact your provider if you do not see a self-service option. Make sure the PTR hostname matches your mail server's HELO/EHLO hostname and has a matching A record.

Does this tool support IPv6?

Yes. Enter a full or shortened IPv6 address and the tool will expand it, build the .ip6.arpa reverse name, and query for the PTR record. IPv6 reverse lookups work the same way as IPv4, just with a longer reverse name.

Can I look up reverse DNS for any IP address?

You can query the PTR record for any publicly routable IP address. Whether a result comes back depends on whether the IP owner has configured a PTR record. Many IPs, especially on residential connections, have generic or missing PTR records.

What does a generic PTR hostname mean?

A PTR hostname like 123-45-67-89.dynamic.isp.net indicates a residential or dynamically assigned IP address. Spam filters treat these as low-trust senders. If you are running a mail server, configure a proper PTR hostname like mail.yourdomain.com instead of using whatever your ISP assigns by default.

Yes. No account required, no rate limits for normal use, and no paywall. The tool queries a public DoH resolver through our edge function. We don't log the IP addresses you look up.

Reverse DNS Lookup — Free PTR Record Checker

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