$ reverse dns lookup
Look up the PTR (reverse DNS) names of IP addresses in bulk and check whether each name resolves back to the same address (forward-confirmed reverse DNS, which mail servers care about). Paste IPv4/IPv6 addresses, or an IPv4 range like 203.0.113.0/24 (up to 256 addresses).
About the ptr tool
Reverse DNS maps an IP address back to a hostname through PTR records in the in-addr.arpa (IPv4) and ip6.arpa (IPv6) zones. This tool looks up PTR names for many addresses at once, expands IPv4 ranges up to a /24, and checks forward-confirmed reverse DNS: whether the name found resolves back to the same address.
How to read the results
A missing PTR is normal for most consumer and cloud addresses. A name that does not resolve forward to the same IP is a weak signal and is a common reason mail servers distrust a sender. Several names on one address are allowed but unusual; the first three are checked.
FAQ
- What is a PTR record?
- A DNS record that maps an IP address to a hostname, the reverse of an A or AAAA record.
- What is forward-confirmed reverse DNS?
- It means the PTR name resolves back to the original IP. Mail systems use it as a basic check that the sender controls both sides.
- Why is there no PTR for my IP?
- Reverse DNS is controlled by whoever owns the address block, usually your ISP or hosting provider. You request changes from them.
- Can I look up a whole subnet?
- Yes, enter an IPv4 range such as 203.0.113.0/24 (up to 256 addresses). IPv6 ranges are too large; list single addresses instead.