How to Create a Correct RDNS (PTR) Record for an Email Server?

Having a correct RDNS (Reverse DNS) or PTR record is critical for your email server to function properly and to prevent your emails from being marked as spam. In this article, we will examine in detail what an RDNS record is, why it is important, and how to configure it correctly.

What is an RDNS (PTR) Record and Why is it Important?

RDNS (Reverse DNS) is a DNS record that maps an IP address to a domain name. Standard DNS (Forward DNS) maps a domain name to an IP address. A PTR record is the technical name for an RDNS record. For email servers, the RDNS record is used to verify that the IP address from which the email originates is associated with a legitimate domain name. This verification plays an important role in the process of spam filters evaluating emails.

Regarding why it is important: Emails sent from an email server without an RDNS record or with an incorrectly configured RDNS record are considered suspicious by spam filters, which can prevent your emails from reaching the recipient's inbox. Many email servers reject connections from IP addresses without an RDNS record or give these emails a lower priority. This can seriously affect your email delivery rates.

In summary, a correct RDNS record:

Increases your email reputation.
Improves your email delivery rates.
Prevents your emails from being marked as spam.
Proves the legitimacy of your email server.

How Does an RDNS Record Work?

When you send an email, the recipient's email server checks the IP address from which the email originates. If there is an RDNS record for this IP address, the server queries this record and learns which domain name the IP address corresponds to. It then checks whether this domain name matches the domain name of the email sending server (for example, the part after @domain.com). If there is a match, the email is considered more trustworthy.

For example, if your email server's IP address is 192.0.2.10 and your domain name is mail.example.com, your RDNS record should map the address 192.0.2.10 to mail.example.com. When the recipient's email server receives an email from the address 192.0.2.10, it will query the RDNS record and receive the answer mail.example.com. If this domain name matches the domain name in the "From" address of the email (for example, [email protected]), the email will be considered more trustworthy.

Steps to Create and Configure an RDNS Record

The process of creating and configuring an RDNS record is usually managed by the internet service provider (ISP) or cloud service provider (AWS, Google Cloud, Azure, etc.) that provides your IP address. In most cases, you cannot create the RDNS record yourself directly, but you can request this process by contacting your ISP or cloud provider.

Here are the steps to create and configure an RDNS record:

Determine Your IP Address: Determine the static IP address or addresses that your email server uses. A static IP address is an IP address that always remains the same. Dynamic IP addresses are not suitable for RDNS records.
Choose Your Domain Name: Determine the domain name that the RDNS record will match. This should usually be your email server's main domain name or a subdomain (for example, mail.example.com).
Contact Your ISP or Cloud Provider: After determining your IP address and domain name, contact your ISP or cloud provider and request the creation of an RDNS record. Tell them the IP address and the domain name you want it to match (for example, 192.0.2.10 -> mail.example.com).
Verification: After the RDNS record is created, it is important to verify that the record is working correctly. You can use various online tools or command-line tools to do this.

Verifying the RDNS Record

You can use the following methods to verify that your RDNS record is configured correctly:

`dig` command (Linux/macOS): Run the following command in the terminal: `dig -x IP_ADDRESS`. For example: `dig -x 192.0.2.10`. This command will query the RDNS record of the IP address and show you the domain name.
`nslookup` command (Windows): Run the following command in the command prompt: `nslookup IP_ADDRESS`. For example: `nslookup 192.0.2.10`. This command will also query the RDNS record of the IP address and show you the domain name.
Online RDNS Check Tools: There are many online RDNS check tools on the internet. You can enter your IP address into these tools to check whether your RDNS record is configured correctly.

If you receive a different domain name or an error message instead of the domain name you expect as a result of the verification, contact your ISP or cloud provider and ask them to fix the problem.

Example Scenarios and Tips

Multiple IP Addresses: If your email server uses more than one IP address, you need to create a separate RDNS record for each IP address.
Subdomain Usage: Your RDNS record does not have to match your main domain name (for example, example.com). It is often more common to use a subdomain such as mail.example.com.
Consistency: Your email server's hostname (server name), your RDNS record, and the domain name in the "From" address you use when sending emails must be consistent with each other. This consistency increases your email reputation.
SPF and DKIM Records: In addition to the RDNS record, configuring SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) records will significantly increase your email reliability. The SPF record specifies which IP addresses are authorized to send emails on behalf of your domain name. The DKIM record adds a digital signature to your emails, verifying that the content of your emails has not been altered.

Conclusion and Summary

Creating a correct RDNS (PTR) record for your email server is vital to improve your email delivery rates, increase your email reputation, and prevent your emails from being marked as spam. In this article, we have examined in detail what an RDNS record is, why it is important, how it works, and how to configure it correctly. Remember that the process of creating and managing an RDNS record is usually managed by your ISP or cloud provider. Therefore, you need to contact them when requesting the creation of an RDNS record. In addition, regularly verifying that your RDNS record is configured correctly and implementing other email authentication mechanisms such as SPF and DKIM will significantly increase the reliability and performance of your email server.