Step::1 Login to WHM root.
Step::2 Navigate to Service Configuration and the open Service Manager.
Step::3 After you reach to Service Manager page, untick the boxes near Exim Mail Server.
Step::4 Click on Save button.
You can execute the below mentioned command as well to do the same.service exim stopThat's It !
Check out the video tutorial to get the procedure in detail. You may check out the blog as well.