What is reverse IP lookup?
Reverse IP lookup — also called reverse DNS lookup or PTR lookup — is the process of resolving an IP address back to its associated domain name. It is the opposite of a standard DNS lookup, which resolves a domain name to an IP address. Reverse lookups rely on PTR (pointer) records stored in a special DNS zone called in-addr.arpa for IPv4 addresses and ip6.arpa for IPv6.
For example, entering the IP address 8.8.8.8 into a reverse lookup tool returns dns.google — the hostname Google has registered for that address. Not all IP addresses have a PTR record configured; it is an optional but highly recommended DNS setting, particularly for mail servers.
What is a PTR record?
A PTR (pointer) record is the DNS record type used for reverse lookups. It maps an IP address to a hostname, and is stored in a reverse DNS zone managed by whoever owns the IP address block — typically the hosting provider or ISP, not the domain owner. To set up a PTR record, you generally need to contact your server or hosting provider and request that they configure it on your behalf.
PTR records must match the forward A or AAAA record of the hostname they point to. If the PTR record says an IP belongs to mail.example.com, then mail.example.com should have an A record pointing back to that same IP. This two-way validation is what email providers check during delivery.
Why is reverse IP lookup useful?
Reverse lookups serve several practical purposes across security, email, and networking. Mail servers routinely perform reverse DNS checks on incoming connections — if an IP has no PTR record, or if the PTR does not match the sending domain, messages are more likely to be flagged as spam or rejected outright. Configuring a correct PTR record for your mail server's IP is one of the most effective steps you can take to improve email deliverability.
Security teams use reverse lookups to investigate suspicious traffic, identify the origin of connections, and check whether an IP is associated with a known malicious host. Network administrators use them to audit infrastructure and verify that servers are correctly identified in DNS.
How to use the reverse IP lookup tool
Enter any IPv4 or IPv6 address in the search field and click Lookup. The tool will query the appropriate reverse DNS zone in real time and return the PTR record registered for that IP, along with its TTL value. If no PTR record exists, the tool will let you know — which itself is useful information when diagnosing email delivery or security issues.
Frequently Asked Questions
What is the difference between an A record lookup and a reverse IP lookup?
An A record lookup starts with a domain name and returns an IP address. A reverse IP lookup does the opposite — it starts with an IP address and returns the associated domain name or hostname. Both lookups are used together to verify that forward and reverse DNS are consistent, a check known as forward-confirmed reverse DNS (FCrDNS).
Why do I need a PTR record for my mail server?
Most major email providers and spam filters check whether the sending IP has a valid PTR record that matches the mail server's hostname. Without one, your outgoing emails are significantly more likely to be rejected or delivered to the spam folder. Setting up a PTR record for your mail server's IP is considered a baseline requirement for reliable email deliverability.
Why does a reverse lookup return no result?
Not every IP address has a PTR record configured. Private IP ranges (like 192.168.x.x or 10.x.x.x) never have public PTR records. Public IPs may also lack PTR records if the hosting provider or server owner has not set one up. If you control the IP and need a PTR record, contact your hosting provider or ISP and request that they add one for you.
Can an IP address have multiple PTR records?
Technically yes, but it is not recommended. Having multiple PTR records for a single IP can cause inconsistent results across DNS resolvers and may trigger spam filters that expect a single, unambiguous reverse DNS entry. Best practice is to configure one PTR record per IP address, matching the primary hostname of the server at that address.
How is reverse DNS different from forward DNS?
Forward DNS resolves names to addresses — it is what happens when you visit a website. Reverse DNS resolves addresses back to names. Forward DNS is managed by whoever controls the domain's DNS zone. Reverse DNS, however, is managed by whoever controls the IP address block — typically the hosting provider or ISP. This is why setting a PTR record requires contacting your provider rather than just updating your own DNS settings.