Free tool · runs in your browser

Reverse DNS & FCrDNS checker

Enter a sending IP to look up its reverse DNS (PTR), confirm that the hostname resolves back to the same IP (FCrDNS), and flag a missing or generic PTR — the exact check mailbox providers run, and the cause behind SMTP 5.7.25. The lookup runs in your browser over DNS-over-HTTPS.

Sending IP (IPv4)

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Findings

Reverse DNS FAQ

What is FCrDNS and why does it matter for sending?+

Forward-Confirmed reverse DNS means an IP's PTR record points to a hostname, and that hostname's A record points back to the same IP. Mailbox providers check this on the sending IP; if it's missing or doesn't match, your mail is penalized or rejected (often with SMTP 5.7.25). Every sending IP needs a matching PTR.

How do I set reverse DNS for my sending IP?+

Reverse DNS is controlled by whoever owns the IP block — usually your hosting/VPS provider, not your domain registrar. Set the PTR to a hostname you control (like mail.yourdomain.com), then make sure that hostname's A record points back to the same IP, and use it as your HELO.

What does a 'generic' PTR look like?+

Provider-default reverse DNS like 203-0-113-10.static.example-isp.net or anything containing the IP digits, 'dynamic', 'pool', 'dsl' or 'customer'. Generic PTRs hurt deliverability — replace them with a branded mail hostname that matches your HELO and forward DNS.

Does this upload my IP anywhere?+

The lookup is performed in your browser via DNS-over-HTTPS to a public resolver to read the public PTR and A records — the same data any mail server sees. No personal data is stored or sent to autopmta.