rDNS (reverse DNS) is used to determine whether a domain is associated with a static IP address. It is most commonly used as an anti-spam measure
If this is something you need for a domain you manage on your dedicated server or VPS, first make sure the server is configured correctly in the Exim Configuration Editor in WHM. Go there, select the “Domains and IPs” tab, and find “Send mail from account’s dedicated IP address”. rDNS can then be set up.
PLEASE NOTE – this is a global setting. EVERY cPanel account with a static IP MUST have rDNS setup for this to work. It’s not per account.
Once that change is made, you will then need to create a support ticket (either through the support system or by emailing us) and request that rDNS be set up for the domain/IP address combo.