How this check works
For an IP address we query its PTR record in in-addr.arpa (IPv4) or ip6.arpa (IPv6). For a host name we first resolve its addresses and check each of them, up to four.
Each PTR name is then resolved forward (A for IPv4, AAAA for IPv6). If the original address is among the results, the reverse DNS is forward-confirmed (FCrDNS).
We also point out names that look automatically generated, such as names that contain the address itself or words like “dynamic” or “dsl”. This is a heuristic: some receivers treat such names as residential connections.
Limitations
- Only public addresses can be checked; private and reserved ranges have no reverse DNS on the Internet.
- PTR records are managed by whoever controls the IP address — usually your hosting or Internet provider — not in your domain’s DNS zone.
- Checked addresses are not stored or logged.
Frequently asked questions
Why do mail servers need reverse DNS?
Many receivers reject or penalize mail from addresses without a PTR record, or whose PTR name does not resolve back. Google’s sender guidelines require valid forward and reverse DNS for sending IP addresses.
How do I set a PTR record?
In the control panel of the provider that owns the IP address (your VPS, cloud or hosting provider), or by asking their support. You cannot set it in your domain’s DNS zone.
Should the PTR name match my HELO name?
It is good practice to use the same fully qualified name for the PTR record, the A/AAAA record and the name your server announces in HELO/EHLO.
What about IPv6?
If your server sends over IPv6, its IPv6 address needs its own PTR and AAAA records. Google’s guidelines apply to IPv6 sending addresses as well.