Thank you D4niel for the reply,
I would like to share what I did, as this may also help others with their set up.
I am using GoDaddy to as my URL host and CloudFanatic as my VPS (Virtual Private Server) provider.
To set rdns in your dashboard hover over Services -> click Manage DNS -> click the RDNS tab -> click the Add PTR button and proceed from there.
In your VPS (in my example CloudFanatic), log in and hover over services and then click “Manage DNS”.
Click on the rDNS tab.
Enter the rDNS information, which should be the FQDN (your subdomain.URL.com, for example).
