DNS & domains
Reverse DNS lookup
Turn an IP address into its hostname, or a hostname into its IP addresses.
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What is reverse DNS?
Normal DNS turns a name into an IP address. Reverse DNS does the opposite: it finds the hostname that belongs to an IP address, using a PTR record. Internet providers often give every customer address a name like host-203-0-113-42.isp.example.
What does "forward-confirmed" mean?
Anyone who controls an IP block can set its PTR record to any name. To trust it, the name should also point back to the same IP address. When it does, it is called forward-confirmed reverse DNS (FCrDNS). Mail servers check this – a mail server without matching reverse DNS is far more likely to be treated as spam.
Can I find all websites on an IP address?
A PTR record gives one name per address. Shared hosting servers can host thousands of websites on one IP, and listing them requires large web-crawl databases, which this free tool does not use.
Why reverse DNS matters for email
Most large mail providers check the PTR record of the server that connects to them. A mail server should have:
- A PTR record for its IP address, such as
203.0.113.25 → mail.example.com. - A matching forward record,
mail.example.com → 203.0.113.25(that is what “forward-confirmed” checks). - The same name used in the server’s HELO/EHLO greeting.
Servers without reverse DNS, or with a generic name like 203-0-113-25.dynamic.provider.net, are much more likely to be rejected or marked as spam. If your emails bounce, check this first, then run our blacklist check.
How to set or change a PTR record
Reverse DNS is controlled by whoever owns the IP address, not by your domain’s DNS provider. That means:
- VPS and cloud servers: most providers let you set the PTR (sometimes called “reverse DNS” or “rDNS”) in the server’s control panel. The forward record must usually exist first.
- Dedicated servers and business lines: ask your hosting company or internet provider to set it.
- Home connections: providers rarely allow custom PTR records. This is one reason home connections are not suitable for running a mail server.
Other uses of reverse DNS
- Reading logs: turning IP addresses into names makes server logs and traceroutes far easier to understand.
- Verifying crawlers: a visitor claiming to be Googlebot should resolve to a name ending in
googlebot.comorgoogle.com, and that name should resolve back to the same IP. Fake bots fail this test. - Identifying networks: provider hostnames often include the city, connection type or customer ID.
Reverse DNS – frequently asked questions
Why does my IP have no reverse DNS?
Providers are not required to create PTR records, and many cloud and mobile addresses have none. It only matters if you run a mail server or another service that is checked by reputation.
Can an IP have more than one PTR record?
Technically yes, but it is discouraged – many systems only read the first one. Use a single PTR that matches your server’s main hostname.
How long does a PTR change take?
Like other DNS records, it depends on the TTL. Changes typically appear within an hour.