Reverse DNS / PTR / FCrDNS Checker
PTR plus forward-confirmed reverse DNS, in one lookup
🔁 Reverse DNS / PTR / FCrDNS Checker
Enter an IPv4 or IPv6 address. We look up the PTR record, then resolve that hostname forward and check whether it points back to the original IP. That round-trip is the FCrDNS check most mail servers run before they accept your mail.
Try an example: 8.8.8.8 · 1.1.1.1 · 2001:4860:4860::8888
Frequently Asked Questions
Common questions about reverse DNS, PTR records, and FCrDNS.
What is a PTR record?
A PTR (pointer) record is the reverse of an A or AAAA record. It maps an IP address back to a hostname. PTR records live in the special in-addr.arpa (IPv4) or ip6.arpa (IPv6) zones. You don't control your own PTR records. Whoever owns the IP block does, usually your hosting provider, ISP, or cloud platform.
What is FCrDNS and why does it matter?
FCrDNS (Forward-Confirmed reverse DNS) is a two-step check. The PTR on the IP returns a hostname, then a forward A or AAAA lookup of that hostname has to return the original IP. When both directions agree, the IP looks legitimate. Gmail, Outlook, and Yahoo all want FCrDNS to pass before they accept your mail. A missing or mismatched PTR is one of the most common reasons mail won't deliver.
I don't have a PTR record. How do I get one?
You don't set PTR records in your own DNS. They live in the reverse zone owned by whoever controls the IP block. Contact your hosting provider, ISP, or cloud platform (AWS, Azure, and GCP all let you set the PTR yourself for elastic IPs) and ask them to point the PTR for your sending IP at a hostname you control. Then add a matching forward A or AAAA record so FCrDNS passes.
What does "FCrDNS Mismatch" mean?
The PTR returns a hostname, but resolving that hostname forward gives a different IP, or none at all. That breaks FCrDNS. Usually it means one of three things: the PTR is pointing at a stale hostname left over from a previous tenant of the IP, you never set a forward A record, or the forward record points at a different IP behind a load balancer. Either fix the PTR or fix the forward record so the two agree.
Does FCrDNS apply to IPv6?
Yes, and Gmail is stricter about it on IPv6 than on IPv4. If you send from IPv6 without a valid PTR, Gmail will reject the mail outright. If you can't set a v6 PTR, send from IPv4 only.