What this tool shows
A reverse DNS lookup takes an IP address and finds the hostname assigned to it through a PTR record. It is the mirror image of a normal lookup. Mail servers rely on it heavily: receiving servers often check that a sending IP has a matching PTR record before accepting mail, so a missing or wrong PTR can hurt deliverability. It is also handy for making sense of raw IPs in server logs.
Frequently asked questions
Why does my IP have no PTR record?
PTR records are set by whoever controls the IP address, usually your hosting provider or ISP, not by your domain's DNS. If none is configured, the lookup returns nothing. For mail servers, ask your provider to add one.
Why does the PTR not match my domain?
Many IPs resolve to a generic hostname assigned by the hosting provider. For a mail server you generally want the PTR to match the hostname it announces, so ask your provider to set it accordingly.
Does reverse DNS work for IPv6?
Yes. IPv6 uses PTR records under ip6.arpa the same way IPv4 uses in-addr.arpa. This tool builds the correct reverse name for both.