Reverse DNS Lookup
Perform reverse DNS lookups — find the hostname associated with an IP address.
About Reverse DNS Lookup
Reverse DNS lookup (rDNS or PTR record lookup) resolves an IP address back to its associated hostname. This is the inverse of a normal DNS lookup (which goes from hostname to IP). Reverse DNS records (PTR records) are configured by the IP address owner in a special DNS zone. They are used in email server authentication (Sender Policy Framework), network troubleshooting, logging (to see hostnames instead of IPs), and identifying the organisation behind an IP address.
FAQ
Why do some IPs have no reverse DNS?
Not all IP addresses have reverse DNS configured. Consumer broadband IPs often have generic PTR records set by the ISP (e.g., 123.456.789.012.isp.com). Cloud and VPS IPs may have no PTR record at all. Email servers should always have a properly configured PTR record that matches their forward DNS — mail servers without matching PTR records are often rejected as spam.