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Reverse DNS Checker

Validate PTR records and Forward-Confirmed reverse DNS (FCrDNS) for your mail server. Essential for email deliverability and sender reputation.

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What is Reverse DNS?

Reverse DNS (rDNS) is the process of resolving an IP address back to a hostname using PTR records. While standard DNS translates domain names like mail.example.com into IP addresses, reverse DNS does the opposite — it tells you what hostname an IP address is associated with.

For email servers, reverse DNS is critically important. When your mail server connects to a recipient's server, the receiving server performs a reverse DNS lookup on your IP address. If there's no PTR record, or if the PTR record doesn't match your server's hostname, many providers will reject the email outright or route it to spam.

Forward-Confirmed reverse DNS (FCrDNS) takes this a step further by requiring a two-way match: the IP must resolve to a hostname (PTR), and that hostname must resolve back to the same IP (A/AAAA record). This prevents spoofing and is required by providers like Gmail and Outlook. Use this tool alongside our SPF Checker, DKIM Checker, and DMARC Checker for complete email authentication validation.

Frequently Asked Questions

What is reverse DNS?
Reverse DNS (rDNS) is the process of resolving an IP address back to a hostname using PTR records in the in-addr.arpa or ip6.arpa DNS zones. Unlike forward DNS which maps hostnames to IPs, reverse DNS does the opposite. Mail servers use PTR records to verify that a sending server's IP address resolves to a legitimate, meaningful hostname — a key signal in spam filtering.
Why do mail servers check PTR records?
Mail servers check PTR records as a basic signal of sender legitimacy. Spammers frequently use dynamically assigned IPs with generic or missing PTR records (like '123-45-67-89.dynamic.isp.net'). A proper PTR record that resolves to a hostname containing your domain name indicates a properly configured, legitimate mail server. Gmail, Outlook, and Yahoo all check PTR records during email delivery.
How do I set up a PTR record?
PTR records are managed by whoever controls the IP address block — typically your hosting provider or ISP, not your domain registrar. Contact your hosting provider and ask them to create a PTR record for your mail server's IP that points to your mail server's hostname (e.g., mail.yourdomain.com). On dedicated servers or VPS providers like DigitalOcean, Linode, or Vultr, you can often set the reverse DNS directly in the control panel.
What should my PTR record say?
Your PTR record should resolve to a meaningful hostname that includes your domain name, such as mail.example.com or smtp.example.com. Avoid generic provider hostnames. The hostname must also have a matching A record pointing back to the same IP — this creates Forward-Confirmed reverse DNS (FCrDNS). The PTR hostname doesn't need to match your domain exactly, but it should be associated with your organization.
What happens if my PTR record doesn't match my hostname?
If your PTR record doesn't match your mail server's hostname (FCrDNS failure), many mail servers will reject your email or assign a high spam score. Gmail returns a temporary '550' error for servers without proper reverse DNS. Outlook/Hotmail rejects email from IPs without matching PTR records. The fix is to ensure the PTR record points to your mail server hostname AND that hostname has an A record pointing back to the same IP.

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