Reverse DNS Lookup (PTR)
Turn IP addresses back into hostnames. We look up each address's PTR record and check that the hostname points back to the same IP — the forward-confirmed reverse DNS test mail servers rely on.
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How to use the Reverse DNS Lookup
- Paste one or more IP addresses, one per line (up to 20, IPv4 or IPv6).
- Click Look up PTR records (or press Ctrl+Enter).
- Check the PTR hostname and the FCrDNS column for each address.
- Copy or download the results as CSV if you need them elsewhere.
Frequently asked questions
What is a reverse DNS (PTR) record?
A PTR record maps an IP address back to a hostname. It lives in a special zone — 8.8.8.8 becomes 8.8.8.8.in-addr.arpa, IPv6 addresses use ip6.arpa — and is controlled by whoever owns the IP range, not by the domain owner.
What is FCrDNS?
Forward-confirmed reverse DNS means the PTR hostname resolves (via A or AAAA) back to the original IP. Anyone can make a PTR claim any name, so only a round trip that matches proves the name really belongs to that server.
Why do mail servers need a matching PTR and FCrDNS?
Receiving mail servers check the sending IP's reverse DNS as a basic anti-spam test. A missing PTR, a mismatch, or a generic ISP name like 1-2-3-4.dynamic.isp.net gets mail rejected or sent to spam by Gmail, Outlook and most filters. Set the PTR to your mail server's name (e.g. mail.example.com) and give that name a matching A/AAAA record.
How do I change the PTR record for my IP?
Ask whoever controls the IP block: your hosting provider, cloud console (AWS, Azure, Google Cloud, DigitalOcean and Hetzner all have a reverse DNS setting) or your ISP. Changing DNS at your domain registrar does not affect PTR records.
Why do private IPs show no result?
Addresses such as 10.x.x.x, 192.168.x.x and 127.0.0.1 aren't on the public internet, so public DNS has no reverse records for them. Only your internal DNS server could answer for those.