Rackspace Cloud Essentials - Creating a Reverse DNS Record

In this article we are going to learn how to add a reverse DNS record (also known as a PTR record) to map your server's IP address to a domain name. The process is fairly simple so let's jump in and add our first reverse DNS record (RDNS).

Why Reverse DNS Lookups?

Reverse DNS records are essential for those running a mail server since many recipient servers reject, or mark as spam, all email that originates from an “unauthenticated” server.

This basically means that after the sending IP address is checked, if the reverse DNS does not match the sending domain, then it is classed as “unauthenticated”.

We put ”unauthenticated” in quotes because having a Reverse DNS record attached to your domain does not automatically guarantee acceptance of email originating from your domain by the recipient's email server. It's just that non-matching or generic reverse DNS lookup settings are often rejected out of hand. Having a reverse DNS record for your domain will prevent email originating from your domain from getting immediately rejected.

RDNS can also be very useful when tracking down network issues and was the original driving force of RDNS. When pinging a website or IP address, one part of the output is the server's RDNS record.

How Does it Work?

When you enter a domain name into your browser, the DNS system will find the IP address of the server the domain is associated with.

A reverse DNS lookup does the opposite. It establishes what domain is associated with the IP address. This is a useful setting to configure for anyone but essential for customers running an outgoing mail server on their Cloud Server.

How Do I Set this Up?

You can easily set up reverse DNS through the control panel. Just perform these steps:

  1. Log in to your Rackspace account.
  2. On the Servers tab, click the link for your Cloud Server from your Servers List.
  3. On the Server Details screen, click Add Recordnext to the Reverse DNS option.

  4. In the resulting window:
    • Enter you domain name (for example “mail.example.com”) in the Hostname field.
    • Set the Time to Live (TTL) for the record.
    • Click Save Record.
  5. Back at the Server Details screen, you will now see 1 Record listed next to the Reverse DNS option. Clicking this link will display the details for the reverse DNS you just added.

Now that you know how to make changes to your DNS configuration, we're going to teach you a useful way to check your settings using the dig command.

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