When you query the Domain Name System (DNS) to determine the domain name associated with an IP address, that is called a Reverse DNS lookup or reverse DNS resolution (rDNS). It is called a “reverse” lookup because it is the reverse of the usual DNS lookup, which is used to determine the IP address associated with a domain name.
DNS lookup: domain = IP
rDNS lookup: IP = domain
Having reverse DNS entries in place is best practice, but it has become especially important for services like email since many mail servers will not accept messages from IP addresses without reverse DNS entries.
To set the reverse DNS records for your GreenGeeks VPS, log in to GreenGeeks and in the “Quick Server Login” section, click the “View Details” button.
Click “Manage RDNS.”
Click the “Hostname” link to configure reverse DNS.
Enter your primary VPS hostname (e.g., vps.ggexample.com) in both fields. Click the green checkbox to save.
DNS changes take a bit of time to propagate throughout the internet, and that period varies depending on a number of factors. Typically though, DNS changes shouldn’t take more than a few hours to propagate.