How to stop access to a subdomain created for an addon domain Print

The following .htaccess code might help

RewriteEngine On
RewriteCond %{HTTP_HOST} ^subdomain.maindomain.com$ [OR]
RewriteCond %{HTTP_HOST} ^www.subdomain.maindomain.com$ [OR]
RewriteCond %{HTTP_HOST} ^addondomain.com$
RewriteCond %{REQUEST_URI} ^/$
RewriteRule ^(.*)$ http://www.addondomain.com/ [R=301,L]

Put this in a .htaccess file and place it in the add-on directories location.