PTR (Reverse DNS) Lookup

Look up PTR records (reverse DNS) for any IP via in-addr.arpa across 12 global resolvers. Free real-time checker.

What is a PTR record?

A PTR record maps an IP address back to a hostname: the reverse of an A/AAAA lookup. It lives under the in-addr.arpa (IPv4) or ip6.arpa (IPv6) zones. Reverse DNS is configured by whoever controls the IP, not the domain owner: typically a hosting provider, ISP, or cloud platform.

When to check PTR records

• Setting up an outbound mail server: many receiving servers reject mail from IPs without proper reverse DNS
• Spam-blocklist debugging: mismatched forward/reverse DNS is a red flag
• Auditing logs to identify the owner of a connecting IP

Reading the results

A PTR result is a hostname (e.g., dns.google for 8.8.8.8). WhereIsDNS lets you enter a bare IP: it auto-converts to the in-addr.arpa form before querying. Multiple PTR records on a single IP are technically legal but rare; most operators publish exactly one.

Common errors and pitfalls

• You can edit forward DNS but not reverse DNS: reverse DNS is controlled by whoever owns the IP block, usually your hosting provider or ISP, not your DNS provider. Most cloud providers (AWS, Google Cloud, Azure, Linode, etc.) let you set PTR through their console.
• FCrDNS mismatch: for mail to work reliably, the PTR's hostname must forward-resolve back to the same IP. 8.8.8.8 → dns.google → A record of dns.google = 8.8.8.8. If the chain breaks, mail filters may flag your sender.
• No PTR at all: many residential and mobile ISPs publish no PTR for end-user IPs. That's normal for clients but problematic if you're running a mail server on that IP.
• IPv6 PTR uses ip6.arpa: different zone from IPv4. WhereIsDNS handles the conversion either way.

FAQ

How do I look up a PTR record?

Just enter the IP: WhereIsDNS auto-builds the reverse-arpa form. Or paste the full 8.8.8.8.in-addr.arpa if you already have it. Both work.

Why do mail servers care about reverse DNS?

Receiving mail servers commonly require that the connecting IP have a PTR record, and that the PTR's hostname forward-resolves back to the same IP ("forward-confirmed reverse DNS," FCrDNS). It's a low-effort spam filter.

Can I have a PTR pointing to multiple hostnames?

Technically yes, but most resolvers (and mail filters) only consider one. If you need multiple names for an IP, publish multiple A records pointing at it instead and pick one as the canonical PTR target.

How do I set a PTR for my server?

It depends on who owns the IP. AWS uses the EC2 console, Linode and DigitalOcean have a "reverse DNS" field on each instance, and ISPs typically require a support ticket. The change is made by the IP owner, not the domain owner.

Background reading

See the DNS Records Explained guide for how PTR fits with mail authentication.