DNS Diagnostics
Reverse DNS Lookup: Find the Hostname for Any IP Address
A reverse DNS lookup queries the PTR record for an IP address to find its associated hostname. This is used for email server verification, network diagnostics, and security analysis. Enter any IP address and get the hostname it resolves to instantly.
Launch in Mission ControlWhat It Measures
This tool performs a PTR (pointer) record lookup for the IP address you provide. It returns the canonical hostname associated with that IP, the time the lookup took, and whether the forward DNS of the returned hostname matches the original IP (FCrDNS verification).
How It Works
- Takes an IP address as input (IPv4 or IPv6)
- Queries the in-addr.arpa DNS zone for PTR records
- Returns the hostname if a PTR record exists
- Performs forward-confirmed reverse DNS (FCrDNS) verification by resolving the hostname back to the IP
Why It Matters
Reverse DNS is critical for email deliverability: mail servers that lack proper PTR records are often rejected or marked as spam by major email providers. Network administrators use reverse DNS to identify devices on their network and investigate suspicious traffic.
Understanding Your Results
A valid reverse DNS entry should return a hostname that forward-resolves back to the same IP (FCrDNS match). For email servers, the PTR record hostname should match the server HELO/EHLO name. Any IP used for email without a PTR record risks high spam scores.
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Run Reverse DNS Lookup Now →Frequently Asked Questions
What is a PTR record?
A PTR (pointer) record maps an IP address back to a hostname. It lives in a special DNS zone called in-addr.arpa and is the DNS mechanism that makes reverse lookups possible. PTR records must be set by whoever controls the IP address block, usually your ISP or hosting provider.
Why does my IP not have a reverse DNS entry?
Most residential ISP addresses and many cloud IP addresses have no PTR record by default. ISPs rarely configure PTR records for dynamic residential IPs. For static IPs, you usually need to contact your ISP or hosting provider to add the record.
How does reverse DNS affect email?
Major email providers like Gmail and Microsoft check that incoming mail servers have a valid PTR record matching their HELO name. Mail from servers without PTR records is often rejected outright or given a very high spam score. Proper reverse DNS is essential for email deliverability.
What is FCrDNS?
Forward-Confirmed Reverse DNS (FCrDNS) means the PTR record resolves to a hostname, and that hostname forward-resolves back to the original IP. This mutual verification is a stronger signal of legitimate infrastructure and is checked by many anti-spam systems.
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