Reverse DNS resolves the PTR record associated with an IP address, returning the hostname that the address maps back to — essential for mail server reputation and log analysis.
Enter an IP address (203.0.113.10) or a hostname (the tool resolves it to an IP first) and run the tool. The probe queries the reverse DNS tree for the matching PTR record.
Input: IP address — e.g. 203.0.113.10.
The output shows the PTR hostname for the IP, or "no PTR record" if none is configured. A missing or mismatched PTR is a common cause of rejected mail — most receiving mail servers require that the sending IP's reverse DNS resolve back to a meaningful hostname.
→ Confirm a mail server IP has a matching PTR before sending.
→ Identify the hostname behind an IP in mail or firewall logs.
→ Verify forward-confirmed reverse DNS for a sending infrastructure.
→ Diagnose mail delivery failures caused by missing reverse DNS.
FCrDNS means the IP resolves to a hostname (PTR), and that hostname resolves back to the same IP (A/AAAA). Mail servers strongly prefer senders with matching FCrDNS; a mismatch is a common reason mail is rejected or sent to spam.
The party that owns the IP allocation — usually your hosting provider or ISP — controls the in-addr.arpa zone. You typically request or configure the PTR through their control panel; you cannot set it in your domain’s forward DNS.
The IP owner has not configured one, or the address is dynamically assigned. For mail servers this must be fixed — request a PTR that matches your mail hostname from your provider.