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🔍 PTR Record · rDNS · in-addr.arpa · Mail Server Verification · FCrDNS

Reverse DNS Lookup

Free reverse DNS lookup tool. Enter any IPv4 address to find its PTR record and hostname. Used to verify mail server identities and diagnose email deliverability issues.

✓ PTR record lookup✓ in-addr.arpa query✓ Hostname resolution✓ Mail server check✓ No signup
What this tool does

Free reverse DNS lookup — find the PTR record and hostname for any IPv4 address

How reverse DNS works and why PTR records matter for email deliverability

This reverse DNS lookup tool constructs the in-addr.arpa query for any IPv4 address and queries it via Cloudflare's DNS-over-HTTPS API. For 8.8.8.8, the query is 8.8.8.8.in-addr.arpa → PTR → dns.google. If no PTR record exists, the tool clearly indicates this, which is important context for diagnosing email deliverability issues.

PTR records are critical for mail servers. Most receiving mail servers check whether the connecting server's IP has a valid PTR record — and ideally that the PTR hostname resolves back to the same IP (FCrDNS). IPs without PTR records are frequently rejected or scored negatively by spam filters. If you're running a mail server and emails are being rejected, checking your IP's reverse DNS is one of the first steps.

Features and capabilities
PTR Lookup
Constructs the correct in-addr.arpa query and retrieves the PTR record.
Shows arpa Name
Displays the full in-addr.arpa query name for transparency.
No-PTR Warning
Clearly flags when an IP has no reverse DNS — common cause of mail delivery failures.
Sample IPs
Quick-load buttons for Google DNS, Cloudflare, and OpenDNS IPs.
Instant Results
Queries complete via Cloudflare DoH in under 1 second.
No Signup
Enter any IP and get results instantly.
FAQ

Frequently asked questions about reverse DNS and PTR records

What is reverse DNS?
Reverse DNS (rDNS) is the process of resolving an IP address back to a hostname — the opposite of a normal DNS lookup which resolves a hostname to an IP. Reverse DNS uses PTR (pointer) records stored in the in-addr.arpa zone. For example, to reverse-lookup 8.8.8.8, the DNS query is made for 8.8.8.8.in-addr.arpa — which returns dns.google. Reverse DNS is maintained by whoever owns the IP address block, typically an ISP or hosting provider.
Why is reverse DNS important for email?
Many mail servers perform a reverse DNS check on connecting mail servers as an anti-spam measure. If the sending server's IP has no PTR record, or if the PTR record doesn't match the server's hostname (forward-confirmed reverse DNS or FCrDNS), the receiving server may reject or flag the email. Most reputable email service providers automatically configure PTR records for their sending IPs. If you run your own mail server, you must ask your hosting provider to set a PTR record for your IP.
What is FCrDNS (Forward-Confirmed Reverse DNS)?
FCrDNS (also called forward-confirmed reverse DNS or full-circle reverse DNS) means the reverse DNS lookup of an IP returns a hostname, and a forward DNS lookup of that hostname returns the original IP. For example: reverse lookup of 1.2.3.4 → mail.example.com, and forward lookup of mail.example.com → 1.2.3.4. FCrDNS is a strong signal that the IP is legitimately associated with the hostname and is required by some strict mail receivers.
How do I set a PTR record for my IP?
PTR records are controlled by the owner of the IP address block, not by the domain owner. If your server is hosted at a cloud provider (AWS, DigitalOcean, Linode, Vultr), you can usually set PTR records in the network settings of your instance. In AWS EC2, go to EC2 → Network Interfaces → select the interface → Actions → Manage IP addresses → set the PTR record. For IPs from your ISP, you need to contact the ISP's technical support or use their customer portal.
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