PTR

networking

Stands for: Pointer record (reverse DNS)

A DNS record that maps an IP address back to a hostname.

A Pointer record (RFC 1035) provides reverse DNS - given an IP, find the name. Mail servers commonly check that a sending IP has a matching PTR as a basic anti-spam signal.

A PTR record maps an address back to a name, which is the reverse of what DNS normally does, and it lives in a special tree built from the address itself. That inversion is why reverse DNS is delegated by whoever owns the address block rather than by whoever owns the domain, so you often cannot set your own PTR without asking your provider.

Its most consequential use is mail. Receiving servers routinely check that a connecting address has a PTR and that the name it returns resolves back to the same address, and mail from a host failing that check is frequently rejected or scored as suspicious. For anyone running a mail server, forward and reverse agreement is not optional hygiene, it is deliverability.

Elsewhere it is a convenience with a trap. Log tools and traceroute display reverse names to make output readable, but a PTR is set by the address holder and proves nothing about who controls the forward name. Trusting it as identity is the mistake; treating it as a label someone chose is correct.

Also known as: ptr, PTR record, reverse DNS

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