What is reverse DNS (rDNS)?
Reverse DNS turns an IP address back into a hostname. A normal DNS lookup asks “what IP does this name use?”; a reverse DNS lookup asks “what name belongs to this IP?” The answer is stored in a PTR record.
How a reverse DNS lookup works
The IP address is written backwards under a special domain, and the lookup asks for its PTR record. IPv4 addresses reverse their four numbers under in-addr.arpa; IPv6 addresses reverse every hex digit under ip6.arpa.
How to find the hostname of an IP address
Enter the IP address above. The lookup returns the hostname from its PTR record, if the network that owns the IP has published one.
- Paste an IPv4 or IPv6 address. URLs, ports and brackets are removed for you.
- Read the hostname and whether it’s forward-confirmed.
- No hostname? That’s normal for many home, mobile and cloud addresses. See why a lookup returns no PTR.
To go the other way, from a hostname to its IP addresses, use DNS Lookup or IP Lookup.
What is a PTR record?
A PTR (pointer) record is the DNS record that maps an IP address to a hostname. It’s the reverse of an A or AAAA record, which maps a hostname to an IP address.
| A / AAAA record | PTR record | |
|---|---|---|
| Direction | Hostname → IP | IP → hostname |
| Lives in | The domain’s own DNS zone | The reverse zone (in-addr.arpa / ip6.arpa) |
| Who edits it | The domain owner, at their DNS host | The owner of the IP block: your host, cloud provider or ISP |
Can an IP have more than one PTR record?
Yes. DNS allows several PTR records for one IP, and the lookup shows all of them. For a mail server, use exactly one: when there are several, receiving servers may pick any of them, which makes results unpredictable.
Forward-confirmed reverse DNS (FCrDNS)
FCrDNS means the check works both ways: the IP’s PTR record gives a hostname, and that hostname’s A or AAAA record includes the same IP. Mail servers use it to confirm a sender isn’t using a borrowed name.
A PTR record should also point to a real hostname with its own A or AAAA record, not to an alias (CNAME). The lookup checks every PTR it finds.
Reverse DNS for email servers
Mail providers check the reverse DNS of every server that connects to them. A missing PTR, a PTR that doesn’t resolve back, or a generic provider-style name are common reasons for email to be rejected or sent to spam.
- Gmail asks all senders for valid forward and reverse DNS, and the sending IP must match the IP of the hostname in its PTR record.
- Spamhaus advises against generic or auto-generated reverse DNS names (like
static-198-51-100-25.host.example.net) for dedicated mail IPs. - Outlook.com requires mail servers to have valid reverse DNS records.
“Reverse DNS does not match SMTP banner”
This warning means your mail server greets other servers with a hostname (its SMTP banner or HELO name) that doesn’t match its PTR record. Make three things use the same name: the PTR record, the hostname’s A record, and the server’s greeting (myhostname in Postfix, primary_hostname in Exim).
| Bounce or warning | Meaning | Fix |
|---|---|---|
550-5.7.25 (Gmail) | No PTR record, or its hostname doesn’t resolve back to the sending IP. | Set the PTR at the IP owner, then add an A/AAAA record for that hostname. |
451 4.7.23 (Gmail) | Temporary deferral for the same reason. | Same fix; Gmail retries. |
550-5.7.1 IPv6 (Gmail) | An IPv6 sender lacks a PTR record or authentication. | Add an IPv6 PTR and AAAA record, or send over IPv4. |
| Reverse DNS does not match SMTP banner | The greeting hostname differs from the PTR. | Use the same name for the PTR, A record and HELO. |
How to set up reverse DNS (PTR record) by provider
Your PTR record is set by whoever owns the IP address, usually your hosting or cloud provider, not by your domain registrar or DNS host. Most providers require the forward A or AAAA record to exist first.
| Provider | Where to set it | Before you start |
|---|---|---|
| AWS (EC2) | Elastic IPs → Actions → Update reverse DNS | An A record must point to the Elastic IP |
| Microsoft Azure | Public IP “reverse FQDN”, set with Azure CLI or PowerShell (not the portal) | The name must resolve to this IP or belong to your subscription; IPv4 only |
| Google Cloud | VM instance → Edit → primary network interface → Public DNS PTR record | Verify the domain (Search Console, or an A record to the VM’s IP) |
| DigitalOcean | Rename the Droplet to the full hostname | The Droplet name becomes the PTR; IPv6 covers the first address only |
| Hetzner | Hetzner Console → server → Networking → edit reverse DNS | For IPv6, set it per address |
| Linode (Akamai) | Linode → Network → Edit RDNS | Forward DNS must already work |
| Vultr | Instance → Settings → IPv4/IPv6 → Reverse DNS | Changes can take hours to spread |
| OVHcloud | Network → Public IP addresses → Configure the reverse DNS | Checks the A/AAAA record immediately |
| Contabo | DNS Management → Reverse DNS Management | IPv6 PTRs are added separately |
| Shared hosting / cPanel | Usually not editable by you | Ask your host to set it |
Menu names change often. Last checked October 2026.
Use Cloudflare or another DNS host for your domain? You still can’t set a PTR there for your server’s IP, because the reverse zone belongs to the IP owner.
Reverse DNS vs reverse IP lookup
Reverse DNS returns the one hostname the IP owner published for an address. A reverse IP lookup tries to list every website hosted on that IP, which needs a separate database of observed DNS records.
This tool does reverse DNS. Many sites call PTR checks “reverse IP lookup”; if you were looking for all the domains on a shared server, that’s a different kind of tool.
Reverse DNS lookup commands
You can run the same PTR lookup from a terminal. These commands return the hostname for an IP address:
| Tool | Command |
|---|---|
| dig (macOS, Linux) | dig -x 198.51.100.24 +short |
| nslookup (Windows cmd, macOS, Linux) | nslookup -type=PTR 198.51.100.24 |
| host (Linux) | host 198.51.100.24 |
| PowerShell | Resolve-DnsName -Name 198.51.100.24 -Type PTR |
| Python | socket.gethostbyaddr("198.51.100.24") |
The result panel fills these in with the IP you checked, ready to copy.
Why a reverse DNS lookup returns no PTR
“No PTR record” is normal for many addresses. Home broadband, mobile and VPN addresses often have none, and many cloud servers only have a default one until you set your own.
- Private addresses like 192.168.x.x or 10.x.x.x have no public PTR. Their names live on your internal DNS.
- No PTR published: the IP owner hasn’t set one. Only they can add it.
- Timeouts: the reverse zone’s servers didn’t answer. That isn’t the same as “no PTR”, so the result says so.
A PTR hostname is a naming hint published by the IP owner, not proof of who uses an address. DomainsMesh is independent and doesn’t identify individuals from IP addresses.
Last updated .