Glossary

PTR Record

Resolves an IP address back to a domain name (Reverse DNS)

A PTR record (Pointer record) performs the reverse of an A record lookup — it maps an IP address back to a hostname, a process known as reverse DNS (rDNS). PTR records are essential for email deliverability and network diagnostics.

What is a PTR Record?

A PTR record, short for Pointer record, is the DNS record type used for reverse DNS lookups. While an A record maps a domain name to an IP address (forward lookup), a PTR record maps an IP address back to a domain name (reverse lookup). For example, a PTR record for the IP 93.184.216.34 might return "example.com".

PTR records are stored in a special zone called the in-addr.arpa zone for IPv4, or the ip6.arpa zone for IPv6. The IP address is written in reverse order as part of the lookup: for the IP 93.184.216.34, the PTR record is looked up at 34.216.184.93.in-addr.arpa. This reversed notation is a quirk of how the DNS hierarchy is organized.

Unlike A records, which are managed by the domain owner, PTR records must be set by the entity that controls the IP address block — typically an ISP, cloud provider, or data center. As a website or mail server operator, you usually need to request PTR record configuration from your hosting provider.

How Does a PTR Record Work?

Reverse DNS lookups follow the same hierarchical delegation model as forward DNS, but the hierarchy flows through the in-addr.arpa domain. IP address blocks are delegated by regional internet registries (RIRs such as ARIN, RIPE, or APNIC) to ISPs and hosting providers, who then maintain the reverse DNS zones for those blocks.

When a mail server receives an email, one of its first checks is to perform a reverse DNS lookup on the connecting server's IP address. If the PTR record resolves to a matching hostname — and importantly, if a forward lookup on that hostname resolves back to the same IP — the mail server considers this a valid forward-confirmed reverse DNS (FCrDNS) match. Servers without valid PTR records are significantly more likely to have their email flagged as spam or rejected outright.

Beyond email, PTR records appear in network diagnostic tools like traceroute and ping, where they translate raw IP addresses in routing paths into meaningful hostnames, making it easier to identify network hops and diagnose connectivity issues.

How to Check a PTR Record

To perform a reverse DNS lookup on any IP address, use the Reverse DNS Lookup tool at nslookup.net/tools/reverse-dns-lookup. Enter the IPv4 or IPv6 address, and the tool queries the appropriate in-addr.arpa or ip6.arpa zone to return the associated PTR record. This is particularly useful for email deliverability troubleshooting, network diagnostics, and verifying that a hosting provider has correctly configured reverse DNS for your server's IP.

Related Tool

Reverse DNS Lookup

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Frequently Asked Questions

Why does my email end up in spam without a PTR record?

Many spam filtering systems check whether the sending IP address has a valid PTR record that resolves back to the sender's hostname. This forward-confirmed reverse DNS check helps verify that the server is legitimately operated rather than a compromised machine or botnet node. Without a PTR record — or with one that does not match — your email is far more likely to be treated as suspicious.

Who controls PTR records?

PTR records are controlled by whoever owns the IP address block, not by the domain owner. If you rent a server from a cloud provider or VPS host, you need to ask them to set the PTR record for your IP to the desired hostname. Many providers let you configure this through their control panel.

What is the difference between forward DNS and reverse DNS?

Forward DNS resolves a domain name to an IP address (using A or AAAA records). Reverse DNS does the opposite — it resolves an IP address to a domain name using PTR records. Both directions exist to provide a verifiable, bidirectional mapping between names and addresses.

How is a PTR record stored in DNS?

PTR records are stored in special reverse zones in DNS. For IPv4, the IP is reversed and appended with ".in-addr.arpa" — so 192.0.2.1 becomes 1.2.0.192.in-addr.arpa. For IPv6, the address is expanded, each nibble reversed, and ".ip6.arpa" is appended. This reversed format allows IP address blocks to follow the same hierarchical delegation model as regular domain names.