Free tool
Find the hostname an IP address maps back to, using its PTR record.
Enter an IPv4 or IPv6 address to find its hostname.
A reverse lookup goes the opposite way to a normal DNS query: instead of resolving a name to an IP, it resolves an IP back to a hostname using a PTR record. Reverse DNS is widely used by mail servers to check that a sending IP has a matching hostname.
Many receiving mail servers reject or downrank mail from IPs with no PTR record. This tool shows the hostname an address currently resolves to.
Reverse DNS lives in special zones. For IPv4 the address is written backwards under in-addr.arpa, so the PTR record for 192.0.2.10 is:
10.2.0.192.in-addr.arpa. 3600 IN PTR mail.example.com.
For IPv6, every hexadecimal digit of the full address is reversed and separated by dots under ip6.arpa, which makes for a long name. You do not need to build either form: enter the address and the lookup does it for you.
PTR records are set by whoever controls the IP range, usually your hosting provider, cloud platform or ISP, not in your own domain's DNS. To change one, look for a reverse DNS setting in your provider's control panel, which many cloud and VPS hosts offer, or ask their support.
Mail servers look for forward-confirmed reverse DNS: the PTR hostname must also resolve back to the same IP. In the example, mail.example.com needs an A record of 192.0.2.10. Check that half with the A record lookup, or the AAAA record lookup for IPv6.
Enter an IPv4 or IPv6 address, such as the address of your mail server. The tool returns the hostname from its PTR record; an address occasionally has more than one, and each is listed on its own row. The lookup runs live from the PulseStack™ server in the UK against Google Public DNS (8.8.8.8), with Cloudflare (1.1.1.1) as the fallback, and nothing is stored.
No PTR record found means the owner of the address has not published one. That is common for home broadband and some cloud addresses, and only a problem if the address sends email.
Private ranges (10.x, 172.16.x to 172.31.x and 192.168.x), loopback addresses such as 127.0.0.1 and other reserved ranges are refused, because there is no public reverse DNS to look up.
A generic hostname, such as one built from the IP address under the provider's own domain, shows that nobody has set a custom PTR. Some spam filters treat a generic name on a mail server as a warning sign.
No PTR on a mail server. Large mailbox providers expect every sending IP to have one, and some refuse mail without it. Ask your host to set a PTR that names your mail server.
PTR and A record do not match. The PTR says mail.example.com, but mail.example.com resolves to a different address, so forward confirmation fails. Make the two agree.
New server, old PTR. After a move, the new address still carries the provider's default name. Set the PTR on the new IP as part of the migration.
Several domains on one IP. An address normally has one PTR, so a server sending for several domains cannot match them all. Give the server one consistent name, such as mail.example.com, use it in both the PTR and the server's HELO greeting, and let each domain's SPF record authorise the IP.
On macOS or Linux, run dig -x 192.0.2.10 +short; dig builds the in-addr.arpa or ip6.arpa name for you. On Windows, nslookup 192.0.2.10 does a reverse lookup automatically, and in PowerShell Resolve-DnsName -Name 192.0.2.10 -Type PTR does the same.
To confirm forward and reverse match, take the hostname from the result and look it up: dig A mail.example.com +short should return the address you started with.
The MX lookup lists the mail servers that receive a domain's email. Look up their addresses, then run each address through this tool to check the whole chain.
Receiving mail servers commonly check that the sending IP has a PTR record, and that the hostname it returns resolves back to the same IP. Missing or mismatched reverse DNS is a frequent reason for mail being rejected or marked as spam.
The owner of the IP address block sets PTR records, which usually means your hosting provider or ISP rather than your domain registrar. To change reverse DNS you normally request it through whoever provides the IP.
Not every IP has a PTR record configured. Residential and some cloud IPs may have generic or missing reverse DNS. For mail-sending IPs, you should ask your provider to set a proper PTR record.
No. Some tools use the name reverse IP lookup for a list of websites sharing an address, built from crawl data. This tool does a reverse DNS lookup: it returns the PTR hostname the owner of the address has published, which is usually a single name.
Every one runs a real check, live, with nothing to install.
PulseStack™ ping and port monitors check a server from London, New York and Sydney and alert you when it stops responding, marking it down only when at least two of the three locations fail. Included from the Starter plan at £9 a month, with a 14-day trial and no card.