Free Reverse DNS (PTR) Record Lookup

Reverse DNS (rDNS) is the process of resolving an IP address back to a domain name using PTR records. While forward DNS maps domain.com to 1.2.3.4, reverse DNS maps 1.2.3.4 back to domain.com. PTR records are stored in the in-addr.arpa zone for IPv4 and ip6.arpa zone for IPv6 addresses.

Many mail servers reject or flag emails from IP addresses without valid PTR records. A properly configured reverse DNS entry tells receiving servers that the sending IP has a verifiable identity. Gmail, Microsoft, and other major providers check PTR records as part of their spam filtering and reputation assessment.

FCrDNS (also called full-circle reverse DNS) verifies that a PTR record's hostname resolves back to the original IP address. For example, if 1.2.3.4 has a PTR record pointing to mail.example.com, FCrDNS checks that mail.example.com's A record points back to 1.2.3.4. This prevents PTR record spoofing.

PTR records are managed by the owner of the IP address block, not the domain owner. Contact your hosting provider or ISP to set up PTR records. For cloud providers like AWS, Azure, or GCP, you can usually configure reverse DNS through their console or by submitting a support request.

Technically yes, an IP can have multiple PTR records, but this is unusual and some mail servers only check the first record returned. For email servers, best practice is to have a single PTR record that matches the server's HELO/EHLO hostname and resolves back to the same IP (FCrDNS).

Without a PTR record, your mail server will likely experience delivery issues. Gmail may defer or reject messages, Microsoft classifies them as suspicious, and many other mail servers reject connections outright. Your emails may be sent to spam folders or blocked entirely. A valid PTR record is considered a baseline requirement for sending email.