PTR record
What is PTR record?
A PTR record is the reverse of an ordinary DNS lookup: it resolves an IP address back to a hostname, stored under the special in-addr.arpa or ip6.arpa zones. AdminKit's Reverse DNS tool looks up a PTR record directly, which mail servers also check before accepting a connection.
By AdminKit team, Netbase JSC · Updated
A PTR (Pointer) record is the reverse of an ordinary DNS lookup: instead of resolving a name to an A or AAAA record’s IP address, it resolves an IP address back to a hostname, stored in the special in-addr.arpa (IPv4) or ip6.arpa (IPv6) DNS zones, both of which IANA administers under the .arpa domain. Mail servers commonly check that an incoming connection’s IP has a PTR record, and that the PTR’s hostname in turn resolves forward back to the same IP (forward-confirmed reverse DNS) — a mismatch or missing PTR record is a common reason legitimate mail gets flagged as spam — Google’s email sender guidelines require a valid PTR record on the sending IP for exactly this reason, and Yahoo’s sender best practices likewise require a valid forward and reverse DNS record for sending IPs. Residential and dynamic IP ranges often have generic, ISP-assigned PTR records rather than ones controlled by the account holder. PTR records and the in-addr.arpa zone are defined in RFC 1035, and RFC 1912 lists a missing or mismatched PTR record among its common DNS configuration errors. Checking a PTR record directly with AdminKit’s Reverse DNS tool is the simplest way to confirm what it currently resolves to.
PTR record is part of AdminKit’s DNS cluster; the full AdminKit glossary lists other related terms.
Frequently asked questions
Why do mail servers check for a PTR record?
An incoming connection's IP lacking a PTR record, or having one whose hostname doesn't resolve forward back to the same IP, is a common reason legitimate mail gets flagged as spam, so mail servers check it as a basic sanity signal.
Can I set my own PTR record on a home or dynamic IP?
Usually not directly -- residential and dynamic IP ranges typically have generic, ISP-assigned PTR records rather than ones the account holder controls.
What is forward-confirmed reverse DNS?
It's the practice of checking that an IP's PTR record resolves to a hostname which, when looked up forward, resolves back to the same IP -- a mismatch is a stronger spam signal than a missing PTR record alone.
Where are PTR records actually stored in DNS?
In the special in-addr.arpa zone for IPv4 addresses or the ip6.arpa zone for IPv6 addresses, rather than under the domain name itself.