You can setup Domain Forwarding from within your cPanel or Plusmail Control Panel.

If you have the EnsimX Pro Control Panel, please follow these 2 steps:

1.  First, park the domain name.

2.  Next, modify the .htaccess file located in your mainwebsite_html directory by adding the following lines:

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} domain.com
RewriteCond %{REQUEST_URI} !subfolder/
RewriteRule ^(.*)$ subfolder/$1 [L]
RewriteCond %{HTTP_HOST} domain2.com
RewriteCond %{REQUEST_URI} !subfolder2/
RewriteRule ^(.*)$ subfolder2/$1 [L]

Replace 'domain.com' with the parked domain name. Replace the 'subfolder' with the folder where the site's files are located.