Find the hostname (PTR record) associated with any IPv4 or IPv6 address. Useful for verifying FCrDNS (Forward-Confirmed Reverse DNS) and mail server configuration.
Reverse DNS (rDNS) resolves an IP address back to a hostname using PTR (Pointer) records stored in special .in-addr.arpa (IPv4) or .ip6.arpa (IPv6) zones. While forward DNS maps names to IPs, reverse DNS maps IPs back to names.
Reverse DNS is configured by the IP address owner (typically an ISP or hosting provider), not the domain owner. Not all IPs have PTR records configured.
Email servers performing spam checks often verify FCrDNS (Forward-Confirmed Reverse DNS) — the process of checking that the PTR record of your mail server's IP resolves to a hostname, and that hostname's A record points back to the same IP.
Missing or mismatched reverse DNS is a common reason for email deliverability issues and spam filtering. Ask your hosting provider to configure a PTR record matching your mail server's hostname.
Reverse DNS (rDNS) is the process of resolving an IP address back to a hostname, the opposite of a standard DNS lookup. It uses special PTR (pointer) records stored in the in-addr.arpa zone for IPv4 or ip6.arpa for IPv6. For example, the PTR record for 203.0.113.1 is stored at 1.113.0.203.in-addr.arpa. Reverse DNS is commonly used by mail servers, intrusion detection systems, and logging tools to identify the hostnames of connecting IPs.
Many mail servers check whether the sending IP address has a valid PTR record that resolves back to the sending domain (forward-confirmed reverse DNS, or FCrDNS). If your mail server's IP has no PTR record, or the PTR does not match the hostname in the SMTP EHLO/HELO command, receiving servers may reject your email or assign a higher spam score. Setting a correct PTR record for your mail server's IP is one of the basic requirements for reliable email delivery.
PTR records are controlled by the owner of the IP address — not the domain owner. For IPs assigned by your ISP or hosting provider, you must request PTR record changes through them. For IP ranges you own (via ARIN, RIPE, APNIC, etc.), you manage PTR records yourself by delegating the in-addr.arpa zone. Cloud providers like AWS, Google Cloud, and Azure allow you to set PTR records through their console or API.
If a reverse DNS lookup returns no result, it means no PTR record has been configured for that IP address. This is common for dynamic IPs and shared hosting environments. For mail servers and other services where reverse DNS is important, the absence of a PTR record can be a deliverability or security flag. Contact your hosting provider or ISP to have a PTR record set for your server's IP.