Free Tool

Reverse DNS Lookup

ISPs check if your sending IP has a valid PTR record pointing to a hostname — and that hostname resolves back to the same IP. A mismatch or missing PTR record causes silent rejections at Gmail, Outlook, and Yahoo. Enter any IP to check.

Understanding Reverse DNS

What is a PTR record?

A PTR (Pointer) record is reverse DNS that maps an IP address back to a hostname. It's the opposite of an A record — while A records map domains to IPs, PTR records map IPs to domains.

What is FCrDNS?

Forward-Confirmed Reverse DNS (FCrDNS) validates both directions: the IP must have a PTR record pointing to a hostname, AND that hostname must resolve back to the same IP. A mismatch fails FCrDNS.

Why does FCrDNS matter for email?

ISPs and mail servers use FCrDNS to reject emails from likely spam servers. Without a valid PTR record or a mismatch, Gmail, Outlook, Yahoo, and others silently reject or flag your emails — even if SPF/DKIM/DMARC pass.

How do I set up a PTR record?

You can't create PTR records yourself in your DNS zone. Contact your hosting provider, ISP, or cloud provider. For AWS, Brevo, Postmark, and others, they often set it up automatically or provide instructions.

Related Free Tools

DNS Record Lookup → Email Blacklist Checker → DMARC Checker → Deliverability Checker →

Why We Built This Tool

ISPs check PTR records as a sender reputation signal. Published PTR records don't resolve instantly, and mismatches between reverse DNS and A records are common after server migrations. This tool performs FCrDNS validation — checking both directions — to surface configuration problems before they impact deliverability.

What Goes Wrong Without This

A missing or mismatched PTR record causes silent email rejections. Gmail, Outlook, and Yahoo block emails from IPs without valid reverse DNS, even when SPF/DKIM/DMARC pass. Teams don't discover the problem until deliverability crashes weeks after changing infrastructure.

Who This Tool Is For

E-commerce & DTC Brands

Verify PTR record setup for dedicated sending IPs — FCrDNS failures cause silent rejections even when SPF/DKIM/DMARC pass.

Email Marketing Agencies

Audit reverse DNS for client sending IPs and whitelabeled SMTP servers. Diagnose deliverability issues tied to missing or mismatched PTR records.

B2B SaaS & Outbound Teams

Validate reverse DNS for outbound servers, cold email sending IPs, and transactional email infrastructure. Catch PTR failures before reputation damage.

Frequently Asked Questions

What is Forward-Confirmed Reverse DNS (FCrDNS)?

FCrDNS validates that the reverse DNS (PTR) and forward DNS (A) records match. The IP must have a PTR record pointing to a hostname, AND that hostname must resolve back to the same IP. A mismatch fails FCrDNS and signals spam server behavior to ISPs.

How does FCrDNS affect email deliverability?

ISPs use FCrDNS as a reputation signal. Gmail, Outlook, Yahoo, and others silently reject or defer email from IPs without valid PTR records or mismatched FCrDNS. Even emails that pass SPF/DKIM/DMARC can be blocked or deferred due to PTR failures.

Can I set up a PTR record myself?

No. PTR records are controlled by the IP owner (your ISP, hosting provider, or cloud provider like AWS). You must contact them to create or modify the PTR record. ESP providers like Brevo, Postmark, and Mailgun often handle this automatically.

Do I need an InboxEagle account to use this tool?

No. This tool is completely free and requires no account or sign-up. InboxEagle provides it as a standalone resource for email marketers, developers, and agencies.

Reverse DNS Missing? Your Reputation Manager Shouldn't Be.

Stop running manual checks. InboxEagle monitors your sender reputation, authentication, and blacklist status 24/7 — and alerts you the moment something breaks.

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