Reverse DNS Lookup
Find the hostname behind an IP address and check that it resolves back to the same address.
How to use this tool and read the results
Enter an IPv4 or IPv6 address and the tool asks DNS for its PTR (pointer) records, the reverse of an A or AAAA lookup. For each hostname found it looks that name up again and tells you whether it resolves back to the address you entered. That round trip is called forward-confirmed reverse DNS.
Mail servers lean on it. A sending server whose address has no PTR record, or whose PTR name does not resolve back to it, is often marked as spam. To find out who owns the address and where it is, use the IP lookup. To see whether an address is on a spam blocklist, use the blacklist checker. The reverse DNS guide shows the same lookup with nslookup and dig.
Frequently asked questions
What is a reverse DNS lookup?
A reverse DNS lookup starts with an IP address and returns the hostname recorded for it, using a PTR record. A normal lookup goes the other way, from a name to an address.
Why does my IP address have no PTR record?
Reverse records live in the zone of whoever owns the address block, usually your internet provider or hosting company. You cannot add one in your own domain's DNS. Ask the provider to set it, or use the control panel if they offer one.
What does forward-confirmed reverse DNS mean?
The PTR hostname resolves, in turn, back to the original IP address. Anyone can claim a name in a PTR record they control, so the match is what shows that the name and address belong together.
Why does a mail server need a PTR record?
Receiving servers often reject or penalise mail from addresses with no PTR record or with one that does not match. Set the PTR to the same name your mail server uses when it says hello (its HELO name).
Can an IP address have more than one PTR record?
Yes, but it is rarely a good idea. Some software only reads the first answer. Mail servers should have exactly one.
Does a reverse lookup show who owns an IP address?
Not reliably. The hostname is whatever the owner of the block chose to publish. For the registered owner and network, use an IP lookup.