DNS PTR Record
Pointer RecordWhat is a PTR Record?
A DNS PTR record (Pointer record) maps an IP address to a domain name, performing the reverse of what an A record does. While an A record resolves a domain name to an IP address (forward DNS), a PTR record resolves an IP address back to a domain name (reverse DNS). This is used to verify the identity of a server by confirming that its IP address maps back to the expected hostname.
PTR records are stored in special reverse DNS zones. For IPv4, the address is reversed and placed under the in-addr.arpa domain. For example, a PTR record for IP 192.0.2.1 would be stored at 1.2.0.192.in-addr.arpa. For IPv6, each nibble of the expanded address is reversed and placed under ip6.arpa. Reverse DNS zones are typically managed by the IP address owner (usually the ISP or hosting provider).
Reverse DNS lookups via PTR records are commonly used in email delivery. Many mail servers reject or flag messages from IP addresses without valid PTR records, as legitimate mail servers are expected to have forward-confirmed reverse DNS (FCrDNS). This means the PTR record should resolve to a hostname, and that hostname's A record should resolve back to the original IP address.
Syntax & Examples
PTR records use reverse DNS zone notation. For IPv4:1.2.0.192.in-addr.arpa. 3600 IN PTR mail.example.com.This means IP address 192.0.2.1 resolves to mail.example.com. The IPv4 address octets are reversed (192.0.2.1 becomes 1.2.0.192) and appended with .in-addr.arpa. For IPv6, each nibble is reversed:4.3.3.7.0.7.3.0.e.2.a.8.0.0.0.0.0.0.0.0.3.a.5.8.8.b.d.0.1.0.0.2.ip6.arpa. 3600 IN PTR host.example.com.This maps the IPv6 address 2001:0db8:85a3::8a2e:0370:7334 to host.example.com.How to Query PTR Records
To query PTR records using dig, use the -x flag for reverse lookups: dig -x 192.0.2.1. This automatically converts the IP to the reverse zone format. For manual queries: dig 1.2.0.192.in-addr.arpa PTR. For concise output: dig +short -x 192.0.2.1. To check IPv6 reverse DNS: dig -x 2001:db8::1.
With nslookup, simply provide the IP address: nslookup 192.0.2.1. On Windows PowerShell: Resolve-DnsName -Name 192.0.2.1 -Type PTR. To verify forward-confirmed reverse DNS (FCrDNS), first do a reverse lookup to get the hostname, then do a forward lookup to verify the hostname resolves back to the same IP: dig -x 192.0.2.1 then dig mail.example.com A.
Related Record Types
Frequently Asked Questions
What is a DNS PTR record?
A DNS PTR (Pointer) record maps an IP address to a domain name, the reverse of an A record. It enables reverse DNS lookups, allowing you to find the hostname associated with a given IP address. PTR records are stored in special reverse zones under in-addr.arpa (IPv4) or ip6.arpa (IPv6).
Why are PTR records important for email?
Many mail servers check the PTR record of the sending IP as an anti-spam measure. If the sending server's IP doesn't have a valid PTR record, or if the PTR hostname doesn't resolve back to the same IP (forward-confirmed reverse DNS), the email may be rejected or marked as spam.
Who manages PTR records?
PTR records are managed by the owner of the IP address block, which is typically your ISP or hosting provider. Unlike forward DNS records that you manage in your domain's DNS panel, reverse DNS records must be set up by whoever owns the IP range. Contact your provider to request PTR record creation.
What is forward-confirmed reverse DNS (FCrDNS)?
FCrDNS means the PTR record for an IP address resolves to a hostname, and that hostname's A record resolves back to the original IP address. For example: 192.0.2.1 → PTR → mail.example.com → A → 192.0.2.1. This bidirectional confirmation is required by many mail servers and security tools.
How do I set up a PTR record?
Contact your hosting provider or ISP and request a PTR record for your IP address. For cloud services like AWS, Azure, or GCP, there are self-service options in the control panel. Provide the IP address and the hostname you want it to resolve to, ensuring the hostname has a corresponding A record pointing back to the same IP.