What is reverse DNS?
Normal DNS turns a name such as example.com into an IP address. Reverse DNS goes the other way: given an address, it returns a name. The answer is stored in a PTR record, published by whoever controls that block of addresses, usually the internet provider or hosting company. For IPv4 the lookup is done on a special name with the digits reversed under in-addr.arpa, which is where the term comes from; IPv6 uses ip6.arpa.
What the hostname can tell you
Providers often build hostnames from the address and their own domain, so a result such as c-73-12-45-9.hsd1.wa.comcast.net hints at the provider and region and suggests a home customer line. Hosting companies show names like ec2-203-0-113-10.compute-1.amazonaws.com, which reveals a cloud server. A mail server's name tells you who runs it. This makes reverse DNS a useful clue when you are investigating where traffic came from, though names are chosen by the owner and can be misleading.
Why many addresses have no PTR record
A PTR record is optional. Plenty of residential and mobile addresses have none, or only a generic one, and addresses on private networks have none that the public internet can see. A missing record is therefore normal and says nothing about whether an address is safe.
Why mail servers care
Email is the place where reverse DNS matters most. Receiving mail servers often check that the sending address has a PTR record, and that the name it returns resolves back to the same address, a test called forward-confirmed reverse DNS. Mail from servers that fail it is more likely to be rejected or sent to spam. If you run your own mail server, ask your provider to set the PTR record; you cannot set it in your own domain's DNS because the block belongs to them.
Reverse DNS is not proof of identity
Whoever controls the address block can set the PTR record to anything. For a reliable view of who owns a block, use the registry record shown by our IP lookup, which includes the holder and the abuse contact.
How to run a reverse lookup yourself
You can do the same check from a command line. On Linux and macOS, dig -x 8.8.8.8 returns the PTR record, and on Windows nslookup 8.8.8.8 does it. Both ask your own resolver, so a result can differ from what a public resolver returns if your provider rewrites or caches answers. This page uses independent public resolvers, which is useful when you suspect your local DNS is misbehaving.
Last reviewed 2026-10-28. Found a mistake? Report a correction (how we handle them).