BRev PTR record — reverse DNS
A PTR record answers the opposite question to everything else in DNS: given an address, what name is it? It lives in a special tree — 93.184.215.14 is queried as 14.215.184.93.in-addr.arpa, with the octets reversed because DNS names are read from most specific to least and addresses are written the other way round.
The crucial consequence of that structure is who controls it. Reverse zones are delegated with the address space, so the PTR for an address belongs to whoever holds the block: your ISP or hosting provider, not you. That is why you cannot add reverse DNS in your own zone file, and why setting it means asking the provider or using their console.
Mail is where it matters most. Receiving servers commonly check that the connecting IP has a PTR record, and that the name it gives resolves forward to the same address — a forward-confirmed reverse DNS check. A missing or mismatched PTR is a strong spam signal, and some servers reject outright. IPv6 uses the same idea with more digits: each of the 32 nibbles is reversed and dotted under ip6.arpa, which is why an IPv6 PTR name is 73 characters long.
What a PTR record looks like
Type 12 · Reverse DNS (IP → name). Zone-file form below — owner name, TTL, then the record and its RDATA.
| Name | TTL | Record | What it means |
|---|---|---|---|
| 14.215.184.93.in-addr.arpa. | 3600 | PTR example.com. | Reverse for 93.184.215.14 — octets reversed under in-addr.arpa. |
| 10.113.0.203.in-addr.arpa. | 3600 | PTR mail1.example.com. | A mail server’s reverse. mail1.example.com must resolve back to 203.0.113.10 for FCrDNS to pass. |
| 1.0.0.…0.8.b.d.0.1.0.0.2.ip6.arpa. | 3600 | PTR host.example.com. | IPv6 reverse: all 32 nibbles reversed under ip6.arpa (abbreviated here). |
The mistakes that break production
Mail from your own server is rejected or marked as spam
Check the PTR first. The sending address must have a reverse record, and that name must resolve forward to the same address. Cloud instances ship with a generic provider PTR (or none), which many receivers treat as an unauthenticated mail source — set it in the provider console to the hostname your server announces in HELO.
Adding a PTR record in your own zone file
It has no effect. The reverse tree is delegated with the address block, so only the holder of that block can publish PTR records for it. The exception is RFC 2317 classless delegation, where a provider delegates a sub-range of a /24 to you explicitly.
Query a PTR record now
The box below is seeded with 93.184.215.14. Choose PTR as the type and press Look up — the query goes from your browser straight to Cloudflare or Google over DNS-over-HTTPS, with no server of ours in the path.
DNS is the internet's address book: it turns a name like example.com into the addresses and service endpoints machines actually connect to. Every record has a type (what kind of fact it states) and a TTL (how long resolvers may cache it).
Record types
| Type | What it stores |
|---|---|
| A | IPv4 address |
| AAAA | IPv6 address |
| CNAME | Canonical name (alias) |
| MX | Mail exchanger (priority target) |
| TXT | Text — SPF, verifications, DKIM, arbitrary data |
| NS | Authoritative nameservers |
| SOA | Start of authority (serial, refresh, retry, expire, minimum) |
| SRV | Service locator (priority weight port target) |
| CAA | Which CAs may issue certificates |
| PTR | Reverse DNS (IP → name) |
| DNSKEY | DNSSEC public key |
| DS | Delegation signer (DNSSEC chain of trust) |
| HTTPS | HTTPS service binding (ALPN, ECH, hints) |
| SVCB | General service binding |
| TLSA | DANE — pin certificates in DNS |
| NAPTR | Name authority pointer (SIP/ENUM) |
TTL & “propagation”
DNS changes don't “push” anywhere — resolvers simply keep the old answer until its TTL runs out, then fetch the new one. So a change “propagates” in at most the old record's TTL. Planning a change? Lower the TTL (e.g. to 300s) a day in advance, make the change, then raise it back. The compare card above shows whether major public caches have picked your change up yet.
FAQ
Why can I not set my own PTR record?
Because reverse DNS is delegated with the IP address space, not the domain. The holder of the address block — your ISP or hosting provider — controls the reverse zone, so the record is set through them.
Does a mail server need a PTR record?
In practice yes. Many receiving servers require a PTR whose name resolves forward to the same address, and treat its absence as a spam signal. It is one of the first things to fix when your own server’s mail is being rejected.
What is in-addr.arpa?
The special domain that holds IPv4 reverse records, with the address octets reversed. IPv6 uses ip6.arpa with each of the 32 hex nibbles reversed and separated by dots.