Reverse DNS
PTR record for an IP address.
About Reverse DNS
Reverse DNS returns the PTR record associated with an IP address. PTR records are the inverse of A and AAAA records, mapping numeric addresses back to hostnames. The result reveals what the IP owner has configured as the canonical name for the address, which often identifies the hosting provider, the datacenter facility, or the specific server role.
When to use it
Mail server administrators check reverse DNS because most receiving servers reject mail from IPs without a valid PTR matching the sender domain. Use this when analysing log files to convert IP addresses into more readable hostnames, helping identify which clients or bots are connecting. Network engineers use rDNS during incident triage to figure out where unexpected outbound connections originate.
How to read the results
A hostname like mail-12345.outbound.protection.outlook.com clearly identifies the source as Microsoft outbound mail. Generic patterns such as 198-51-100-1.static.example-isp.net indicate a static IP from a specific ISP. If the result returns the IP unchanged or shows nothing, no PTR is set. Forward-reverse confirmed records, where the PTR target resolves back to the same IP, signal a properly maintained network.
Frequently asked questions
Why does my IP not have a PTR record? ▾
Reverse DNS is configured by the IP owner, usually the ISP or hosting provider. Many small VPS providers do not set PTR records by default. To add one, contact your provider or check if their control panel offers an rDNS setting for your assigned IP.
Can I set a custom PTR record myself? ▾
Only the network owner can delegate PTR control. If your provider supports it, you can request a custom value pointing at your domain. AWS, Google Cloud, Azure, and most reputable hosts offer this through their console.
Why is reverse DNS important for email? ▾
Spam filters use reverse DNS as a basic authenticity check. A sending IP without a PTR, or with a generic ISP PTR that does not match the From domain, scores higher as spam. Properly aligned rDNS is one of the cheapest ways to improve inbox delivery.
Is forward-reverse confirmed different from a regular PTR? ▾
Forward-reverse confirmed means the PTR hostname resolves back to the same IP that owns it. Many mail systems require this match. A misaligned PTR, where the hostname points elsewhere, is rejected as suspicious.