Reverse DNS (rDNS)

Verifies that the IP has a PTR record (the reverse mapping from IP to hostname). Most large mail receivers (Gmail, Outlook, Yahoo) reject or heavily penalize mail from IPs that have no rDNS at all. PTR records are also a baseline expectation for any "real" mail server.

Applies to: IPv4 and IPv6 hosts.

How It Works

We do a PTR lookup on the IP. If at least one PTR record exists, the check passes. If none exists, the check fails.

Fails On

• No PTR record published for the IP.

Related Checks

• Forward-Confirmed Reverse DNS (FCrDNS) - the next step up; verifies the PTR target resolves forward back to the original IP.
• Generic PTR Pattern - flags PTRs that look like dynamic / consumer IP ranges.
• PTR Hostname Format - flags malformed PTR hostnames.