Reverse DNS Lookup
What Is Reverse DNS?
Reverse DNS (rDNS) is the process of looking up the hostname associated with an IP address. While a standard DNS lookup translates a domain name like example.com into an IP address, a reverse DNS lookup does the opposite - it takes an IP address and returns the associated domain name. This is accomplished by querying PTR (Pointer) records in the DNS system.
PTR records are stored in special reverse lookup zones. For IPv4 addresses, these zones use the in-addr.arpa domain. The IP address octets are reversed and appended to in-addr.arpa to form the query. For example, looking up 203.0.113.42 queries 42.113.0.203.in-addr.arpa. For IPv6 addresses, the ip6.arpa domain is used with each hexadecimal digit reversed and separated by dots.
Reverse DNS is particularly important for email servers. Most major email providers, including Gmail, Outlook, and Yahoo, check the reverse DNS of the sending server's IP address as part of their spam filtering. If the sending IP has no PTR record, or if the PTR hostname does not resolve back to the same IP (a forward-confirmed reverse DNS check), the email is more likely to be flagged as spam or rejected outright. Setting up proper reverse DNS is a fundamental step in email deliverability.
Unlike forward DNS records that are managed by domain owners, PTR records are controlled by the IP address block owner - typically your ISP or hosting provider. To set up a PTR record for your server, you need to contact your provider or use their control panel. Most residential ISPs do not offer PTR record configuration for customer IP addresses, which is one reason why sending email from a home connection is unreliable.
Our reverse DNS tool queries Cloudflare's global DNS infrastructure to find PTR records quickly and accurately. After checking reverse DNS, you might want to use our DNS Lookup tool to verify forward DNS, check if the IP is on any spam blacklists, or find out more about the IP with What Is My IP.
Frequently Asked Questions
What is a reverse DNS lookup?
A reverse DNS lookup is the opposite of a regular DNS lookup. Instead of translating a domain name to an IP address, it translates an IP address back to a hostname by querying PTR (Pointer) records. For example, looking up 8.8.8.8 returns dns.google as the hostname.
What is a PTR record?
A PTR (Pointer) record is a DNS record that maps an IP address to a hostname. PTR records are stored in a special reverse DNS zone. For IPv4, the zone uses the in-addr.arpa domain, and for IPv6, it uses ip6.arpa. PTR records must be configured by the owner of the IP address block, typically the ISP or hosting provider.
Why is reverse DNS important for email?
Many mail servers check the reverse DNS of the sending server's IP address as part of spam filtering. If the IP address does not have a valid PTR record, or if the PTR hostname does not match the sending domain, the email may be marked as spam or rejected entirely. Proper reverse DNS setup is essential for email deliverability.
Why does my IP not have a PTR record?
PTR records are not automatically created. They must be set up by whoever controls the IP address block, usually your ISP or hosting provider. Most residential ISPs do not configure PTR records for customer IPs. If you need a PTR record for a server, contact your hosting provider or configure it through their control panel.