Reverse DNS answers the opposite question to a normal lookup. Instead of “what address does this name point to?”, it asks “what name does this address point to?”. The answer comes from a PTR record, and you can read it for any IP with the reverse DNS lookup.
Forward and reverse
A normal, forward lookup takes a hostname like mail.example.com and returns an IP address. Reverse DNS goes the other way: give it 198.51.100.4 and it returns the hostname that address claims to be. The two are stored and controlled separately, which is the source of a lot of confusion, so it is worth being precise about how the reverse side is built.
The reverse zone
IP addresses do not have names directly. Reverse DNS works by turning the address into a special domain name and looking up a PTR record there.
For IPv4, the four octets are reversed and placed under in-addr.arpa. So 198.51.100.4 becomes:
4.100.51.198.in-addr.arpaFor IPv6, each of the 32 hex nibbles is reversed and placed under ip6.arpa. The principle is the same; the name is just much longer. The reverse DNS lookup builds this pointer name for you, so you can paste in the plain address.
Who controls it
This is the part that trips people up. A forward record is set by the domain owner. The reverse record is set by whoever owns the IP block — your hosting provider, cloud platform or ISP. You can buy a domain and point it wherever you like, but you cannot set reverse DNS for an address you do not control. If you run a server and need a specific PTR, you ask your provider to set it, often through a control panel field labelled “reverse DNS” or “PTR”.
Why mail servers care
Reverse DNS matters most for sending email. When your mail server connects to a receiver, the receiver often looks up the PTR record for your IP and checks two things:
- Does the address have a PTR at all? A missing one is a weak signal of a spammy or misconfigured sender.
- Does the PTR hostname look legitimate, and does it forward-confirm — that is, does the hostname in the PTR resolve back to the same IP through its A or AAAA record?
A generic, provider-assigned name like 203-0-113-8.dynamic.example-isp.net is a common reason mail lands in spam or is refused outright. A clean, forward-confirmed hostname that matches your mail domain is one of the quiet things that keeps delivery healthy.
When no PTR is fine
Outside of mail, a missing PTR is usually nothing to worry about. Plenty of perfectly healthy addresses have no reverse DNS, and the lookup returning “no PTR record” is a normal answer rather than a failure. The places it genuinely matters are mail servers and the occasional service that insists on forward-confirmed reverse DNS for access.
Multiple PTR records
An address can technically have more than one PTR record, though it is uncommon and some software handles it badly. For mail in particular, a single, forward-confirmed hostname is the cleanest arrangement. If you see several PTR records on an address you control, it is usually worth trimming them to one.
Checking it
To read the reverse DNS for any address, enter it into the reverse DNS lookup. It converts the IPv4 or IPv6 address to its in-addr.arpa or ip6.arpa pointer, queries the PTR record live over secure DNS, and shows the hostname it resolves back to. If there is no record, it says so plainly. The query runs in your browser and nothing you enter is stored.
If you are working on email specifically, pair this with an MX lookup to see where a domain receives mail and a full DNS lookup to read the rest of its records in one place.