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Reverse DNS Lookup

Resolve an IP address to its PTR hostname and verify forward-confirmed reverse DNS for mail servers.

Try

Fix it here

This builds the change the checks above ask for, and validates it against the same rules.

Reverse DNS (PTR) record and request

The PTR line for a sending address, the forward record that makes it confirm, and the request to send whoever announces the address — because the reverse zone is never yours.

Reverse DNS hangs off an IP address, not off a domain, so this has to be the address a receiving server sees on the connection — behind NAT that is your network's public address, not the one on the server's own interface.

About the reverse dns lookup

A forward DNS lookup turns a hostname into an IP address; reverse DNS does the opposite, mapping an IP address back to a hostname through a PTR record. Unlike forward records, PTR records live in a special reverse zone tied to the IP address block and are almost always controlled by whoever owns that block, typically your hosting provider or ISP, not your own domain's DNS.

This tool looks up the PTR record for an IP address and, when relevant, also checks forward-confirmed reverse DNS (FCrDNS): whether the hostname the PTR record returns resolves forward, via an A or AAAA record, back to the same IP address. A match confirms both directions agree, which many mail servers treat as a basic sanity check before accepting a connection.

For mail servers specifically, a missing or mismatched PTR record is one of the most common reasons a receiving server rejects or heavily penalizes a connection, since a sending IP with no reverse DNS at all looks similar to how a compromised residential machine or a fresh, unvetted cloud instance would appear. Because the reverse zone belongs to the network owner rather than the domain owner, setting or fixing a PTR record means contacting your hosting provider or ISP's support or control panel, not editing your domain's own DNS zone where the forward records live.

Common questions

What is a PTR record?
A DNS record in the special reverse zone that maps an IP address back to a hostname, the reverse of what an A or AAAA record does.
Why does my mail server need it?
Many receiving mail servers reject or penalize connections from IP addresses with no matching reverse DNS, since a missing PTR record is a common pattern among compromised or unvetted senders.
How do I set a PTR record?
Your hosting provider or ISP controls the reverse zone, not your domain's own DNS. Ask their support team or use their network control panel to set it.
What is forward-confirmed reverse DNS?
A check that the hostname a PTR record returns for an IP also resolves forward, via an A or AAAA record, back to that same IP, confirming both directions agree.
What this tool checks (4 rules)
  • email.rdns.generic-hostname — Reverse DNS looks like a generic provider-assigned name
  • email.rdns.name-mismatch — Reverse DNS name does not match the mail server's own hostname
  • email.rdns.no-ptr — Mail server address has no reverse DNS (PTR) record
  • email.rdns.not-forward-confirmed — Reverse DNS does not confirm forward (no full-circle match)