Free reverse DNS lookup
Reverse DNS lookup
A reverse DNS lookup, or PTR lookup, for any IPv4 or IPv6 address: find its host name, and check that the name points back to the same address.
How it works
How a reverse lookup works
- 1Reverse the address
For 8.8.4.4 the tool asks for 4.4.8.8.in-addr.arpa. IPv6 addresses are written out digit by digit under ip6.arpa.
- 2Ask for the PTR record
The resolver returns the host name the owner of the address block published, such as dns.google.
- 3Check it forward
The tool then looks up that host name and confirms it points back to the same IP address.
Why reverse DNS matters for email
Google’s sender guidelines require that the IP address of a sending mail server has a PTR record, and that the host name in it resolves back to the same address. Without that, Gmail may reject the mail or send it to spam.
If you send through a service such as Google Workspace, Microsoft 365 or Amazon SES, the provider sets this up for its own servers. It matters when you run your own mail server or send from a dedicated IP.
DNS tools
More DNS tools
Look up every DNS record for a domain, or check the MX records that receive its mail.
FAQ
Reverse DNS lookup, answered
Anything we have not answered here, ask us directly. A senior engineer replies.
What is a reverse DNS lookup?
A normal DNS lookup turns a name into an IP address. A reverse lookup does the opposite: it asks for the PTR record of an IP address and returns the host name the owner of that address has set.
What is a PTR lookup?
A PTR lookup is the DNS query behind a reverse DNS lookup. It asks for the PTR (pointer) record of an IP address, which holds the host name. The two terms mean the same thing.
What is forward-confirmed reverse DNS?
It means the PTR name also points back to the same IP address in an A or AAAA record. Mail servers check this, and Gmail requires it for every sender.
Why does my server’s IP have no PTR record?
PTR records are set by whoever owns the IP address block, usually your hosting or cloud provider, not in your own domain’s DNS. Ask your provider, or look for a reverse DNS setting in their control panel.
Does it work with IPv6?
Yes. Enter an IPv6 address in any standard form. The tool expands it and asks for the PTR record under ip6.arpa.
Can a reverse lookup tell me which websites are on an IP?
No. An IP address has at most a few PTR names, set by its owner. Many websites can share one address, especially behind a CDN such as Cloudflare, and DNS does not list them.
Free tools
More free tools
Days between dates, add or subtract time, an age calculator, a live countdown, the day of the week and ISO week numbers.
DomainsDNS lookupEvery DNS record for a domain, a propagation check across four resolvers, a subdomain finder and reverse IP lookup.
EmailSPF, DKIM and DMARC checkerScore a domain’s email authentication out of 100, with SPF, DKIM, DMARC, MTA-STS and BIMI, plus SPF and DMARC generators.
SEOSchema markup generatorJSON-LD for 13 schema.org types with a worked example for each, and a validator for the markup already on a page.
TimeTime zone converterSee a time in every city you work with, with offsets, daylight saving and working hours.
DatesBusiness days calculatorWorking days between two dates, or business days added to a date, for any weekend pattern.
Dude Lemon
Contact Dude Lemon
Dude Lemon is a software development company. We build web apps, mobile apps and AI software for businesses.