What is a reverse DNS lookup?

A reverse DNS lookup queries the PTR record for an IP address to find the hostname it maps back to. This is the opposite of a normal DNS lookup, which converts a hostname to an IP.

What is forward-confirmed reverse DNS?

Forward-confirmed reverse DNS (FCrDNS) means the PTR record of an IP resolves to a hostname, and that hostname's A record resolves back to the same IP. This is required by many mail servers and helps establish that an IP is legitimate.

Why would my IP have no PTR record?

Many residential and cloud IP addresses have no PTR record by default. For mail servers, a missing or non-matching PTR record often causes emails to be rejected or marked as spam. Contact your ISP or cloud provider to set a PTR record.

PTR Record Lookup

Reverse DNS Lookup

Find the hostname (PTR record) that any IP address resolves to, and verify forward-confirmed DNS.

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Reverse DNS — What PTR Records Do

A PTR (pointer) record is the reverse mapping of an IP address to a hostname. While a standard A record maps example.com → 203.0.113.1, a PTR record maps 203.0.113.1 → mail.example.com. PTR records live in the special in-addr.arpa zone for IPv4 and ip6.arpa for IPv6.

Why PTR Records Matter for Email

Most mail servers perform a reverse DNS check on incoming connections. If an IP has no PTR record, or the PTR hostname does not forward-resolve back to the same IP (FCrDNS failure), the email may be rejected or assigned a high spam score. Setting a matching PTR record is one of the first steps to improving email deliverability from a new server.

Forward-Confirmed Reverse DNS (FCrDNS)

FCrDNS means IP → PTR → hostname → A record → same IP. This bidirectional check is used by spam filters to verify that a sending server is legitimate. A PTR record that doesn't resolve back is worse than no PTR at all for some filters.

Who Controls PTR Records?

PTR records are controlled by whoever owns the IP block — usually your ISP, data centre, or cloud provider — not by you. To set a PTR record, you must request it through your provider or use their control panel (AWS, GCP, Hetzner etc. all offer this).