How to set reverse DNS (PTR) for many IP addresses and check forward-confirmed rDNS?

Updated: 28 September 2026 · Applies to: Self-managed dedicated servers with the Ucartz client area

Reverse DNS (rDNS or PTR) turns an IP address back into a host name. Mail servers, security tools and many partner systems look at it, so it is good practice to set it for every address that your server uses to send or receive traffic from. This guide shows how to set it for many addresses, how to name them, and how to check that the forward and reverse records agree.

What is "forward-confirmed" reverse DNS?

A complete setup has two matching records:

• PTR (reverse): 203.0.113.11 points to mail1.example.com.
• A (forward): mail1.example.com points back to 203.0.113.11.

When both agree, the setup is called forward-confirmed reverse DNS (FCrDNS). Gmail asks senders for valid forward and reverse DNS records, and Yahoo asks for valid, meaningful, non-generic PTR records for all sending IPs. A generic name such as 203-0-113-11.some-provider.net does not count as meaningful.

1. Choose a naming scheme

Give every address its own name in a domain you control, for example:

203.0.113.10  server1.example.com
203.0.113.11  mail1.example.com
203.0.113.12  mail2.example.com
203.0.113.13  app1.example.com

Use names that describe the job. Names should be lower case and use only letters, digits and hyphens.

2. Create the forward (A) records first

In the DNS of your domain, add an A record for each name that points to its address. On cPanel hosting use the Zone Editor (see How to Add an MX Record in cPanel DNS Zone Editor for how it works). Wait until dig +short mail1.example.com returns the address.

3. Set the reverse (PTR) record in the client area

1. Log in to the Ucartz client area and open Services › My Services, then your dedicated server.
2. Open Configure Reverse DNS (where it is shown for the service) and click Edit next to each IP address.
3. Enter the host name and save. Repeat for every address.

The full steps are in How to setup rDNS using Ucartz client area?. Changes can take a few hours to be visible.

If an address of an additional subnet is not shown, or if you have dozens of addresses, open a support ticket with a plain list like the one above (IP address, then host name, one per line) and ask for the reverse DNS to be set.

4. Check one address

dig -x 203.0.113.11 +short
dig +short mail1.example.com

The first command must print mail1.example.com. and the second the address.

5. Check many addresses with a script

#!/bin/bash
# usage: ./check-rdns.sh 203.0.113.10 203.0.113.11 ...
for ip in "$@"; do
  ptr=$(dig -x "$ip" +short | head -1 | sed 's/\.$//')
  if [ -z "$ptr" ]; then echo "$ip  NO PTR"; continue; fi
  fwd=$(dig +short A "$ptr" | tr '\n' ' ')
  if echo "$fwd" | grep -qw "$ip"; then echo "$ip  OK   $ptr"; else echo "$ip  MISMATCH  $ptr -> $fwd"; fi
done

Make it executable (chmod +x check-rdns.sh) and run it after every change. To run it automatically, see How to monitor your sending IP addresses automatically with a script?.

6. Use the same name for the HELO

A mail server should introduce itself with the name of the address it uses. See How to make Postfix send from a specific IP address with a matching HELO name?.

Common problems

• PTR shows the old name: DNS caches keep the answer for a while. Query the authoritative server or wait.
• MISMATCH: the A record is missing or points to another address. Fix the A record.
• Two addresses with the same name: give each address its own name.
• The name belongs to a domain you do not control: use your own domain so that you can create the A record.

Frequently asked questions

Do all addresses need rDNS?
Set it at least for every address that sends mail or accepts connections from partners. It is easy to do for all of them.

Can I use a name in a domain that is hosted elsewhere?
Yes. The A record can be at any DNS provider; the PTR record is set in the Ucartz client area.

Need a dedicated server, more IP addresses, or a hand with the setup?

• Unmanaged dedicated servers: full root access and IPv4 subnets from /29 up to /24, ordered with the server or added later.
• Managed dedicated servers: our team looks after the operating system, updates, security and monitoring.
• Dedicated server locations: choose the country and data centre when you order.

Prefer a hand with the setup? Our engineers can do it for you: Hire an Expert, or use our on-demand server management.