DNS · PTR · FCrDNS

Reverse DNS and PTR check

Check the reverse DNS PTR record for an IP address and verify whether the PTR hostname resolves forward back to the same IP address.

PTR records are especially important for mail servers. Forward-confirmed reverse DNS means that the PTR hostname resolves forward back to the original IP address.

Enter a public IPv4 or IPv6 address.
Guide · Reverse DNS

What is a PTR record?

A PTR record is a reverse DNS record that maps an IP address back to a hostname. A normal A or AAAA record maps a name to an IP address, while PTR works in the opposite direction: from IP address to name.

Reverse DNS is important for mail servers, log analysis and identifying server infrastructure. Many receiving mail systems check whether the sending server IP has a meaningful PTR record.

PTR

PTR shows which hostname an IP address returns in reverse DNS. For example, an IP address may return mail.example.com.

FCrDNS

Forward-confirmed reverse DNS verifies that the PTR hostname resolves forward back to the original IP address.

Email

A missing or inconsistent PTR record can reduce the trustworthiness of a mail server in the eyes of receiving systems.

IPv4 and IPv6

This tool supports both IPv4 and IPv6 addresses and checks forward A and AAAA records for the PTR hostnames.

How to interpret the result

If a PTR record exists and FCrDNS is valid, the IP address maps to a hostname that resolves forward back to the same IP address. This is usually the desired state for mail servers.

If PTR exists but FCrDNS does not match, reverse DNS exists but the hostname’s A or AAAA records do not point back to the original IP address. In that case, the DNS configuration should be reviewed.

Common issues

  • The IP address has no PTR record.
  • The PTR record points to an old or incorrect hostname.
  • The PTR hostname does not resolve back to the same IP address.
  • IPv6 reverse DNS has a different status than IPv4 reverse DNS.

Frequently asked questions

Is a PTR record required?

It is usually not required for a website, but it is strongly recommended for mail servers.

What does FCrDNS mean?

FCrDNS means that the PTR hostname is checked forward using A or AAAA records and should resolve back to the same IP address.

Who controls the PTR record?

PTR records are usually controlled by the owner of the IP address or hosting provider, not by the administrator of the normal domain DNS zone.