Hello Laeek,
So the end user quarantine is going to notify users about new messages via email. So as long as you have this set up correctly, they will get notified. For logging in to look at their messages, it is going to be using the UI. So in this case it will be using either port 41080 or 41443. Since you say they are using a VPN, they should be able to access this as long as they can get to the UI from the local environment.
Hope this helps.
Please note my edit.
Message Edited by TomC on 02-06-2009 07:53 AM