If you change the mail host of a domain already configured on your cPanel server, you must change the email routing so that mail is sent to the correct server.
- Log into WHM as the 'root' user.
- Navigate to "Home » DNS Functions » Email Routing Configuration."
- Select the domain from the "Choose a Domain to Edit" dropdown menu.
- Click the "Edit" button.
- Select the "Local Mail Exchanger" or "Remote Mail Exchanger" option.
- Click the "Save" button.