As a preventative measure against bulking during email delivery, it is critical to ensure that reverse DNS and PTR records are setup and properly configured. The most common reason for establishing a reverse DNS record is to add credibility to the email server sending outbound mail. Reverse DNS adds further tracing to the origin of an e-mail and some incoming mail servers will not accept mail from IPs without a reverse DNS. This article details how to setup a proper reverse DNS zone, as well as create a PTR record, to improve email delivery.
To create the reverse DNS zone:
You must create the reverse DNS zone of the authoritative DNS nameserver for the main IP address of your server. To do so, perform the following:
- Enter the IP address you're trying to configure into the DIG Web Interface Tool.
Note: If the Reverse response is not provided by your nameserver, you’ll need to contact your ESP to help you set a PTR record. Email their support team and let them know you would like a PTR record set for the IP address X.X.X.X resolving to yourdomain.example.com.
- If you control the authoritative nameserver, first create a DNS zone in the specific format.
EX: If your IP address is 192.168.0.100, start by dropping the final octet (last set of numbers) to give you 192.168.0. Then reverse the fragment of the IP address, giving you: 0.168.192.
Note: Hostname format should start with a portion of your IP address written backward followed by .in-addr.arpa.
- Append in: .in-addr.arpa.
EX: Complete reverse zone domain of: 0.168.192.in-addr.arpa.
To create the PTR Record:
- Add a new PTR record. For the name, enter the final digit of the IP address that you’re setting up the reverse record for.
- For the Canonical Hostname, enter the domain you’d like the IP address to resolve
- After you've saved your file zone, allow time for the change before validating the new reverse DNS record.
Note: If configured properly, you should see something similar to the following next time you run the DIG Web Interface Tool: 18.104.22.168.in-addr.arpa.6230 IN PTR mailserver.example.com