Ordinary DNS goes from name to address: www.example.com → 192.0.2.10. Reverse DNS goes the other way: from an IP address to a name. Mail servers, logs, traceroute and many tools use it to show who an address belongs to.
The PTR record
The answer is stored in a PTR record (pointer). Because DNS delegates from right to left, the address is written backwards under a special zone:
- IPv4:
192.0.2.10→10.2.0.192.in-addr.arpa - IPv6: each hexadecimal digit separately, backwards, under
ip6.arpa
Looking up the PTR record for that name returns the host name, for example server.example.com. The IP converter shows the reverse name for any address.
Who can set it
This is the big difference from ordinary DNS. Reverse zones follow address blocks, not domains. The PTR record for an address is set by whoever holds the block — your ISP, hosting or cloud provider — not by whoever manages your domain.
- For a server at a hosting provider, change the PTR in their control panel, often under “rDNS” or “Reverse DNS”.
- For an ordinary home connection the provider decides, and the name is often something generic that contains the address.
Forward confirmation
Since the holder of a block can put any name in the PTR record, a PTR alone proves little. Many systems therefore check that the name resolves back: the PTR for 192.0.2.10 says mail.example.com, and the A record for mail.example.com is 192.0.2.10. That’s forward-confirmed reverse DNS (FCrDNS). The reverse DNS tool checks it for you.
Why email cares
Large mail providers often reject or down-rank mail from servers with no reverse DNS, or whose PTR name doesn’t match the forward lookup. Running your own mail server therefore needs:
- a static IP address,
- a PTR record pointing to the server’s name,
- an A or AAAA record for that name pointing back to the same address,
- plus SPF, DKIM and DMARC in TXT records.
If your address has no PTR record
That’s common and not a fault for a home connection. Many broadband and mobile networks publish no reverse DNS at all, or only generic names. It doesn’t affect browsing.
Look up any address with reverse DNS, or read more about PTR records.