Hi,
As mentioned earlier, I'm using a proxy.pac.
Does the pac fille needs to be accessible from outside, or only from the BES server ?
Edit: Answer is no, the proxy.pac doesn't need to be accessible from outside. I changed the configuration and I'm now able to access my local servers. Still need to figure out why I cannot access the internet anymore though

I followed those steps to enforce the browser to follow my rules:
To ensure all data travels via the MDS service perform the following I.T Policy changes:
1. Device-Only Items > Enable WAP Config = False. This will remove the carriers WAP browser (i.e. Telstra Business Portal will be removed)
2. Browser Policy Group > MDS Browser Title = <company name> Internet (e.g. BBForums Internet). This clearly identifies the MDS browser to users.
3. Browser Policy Group > Allow IBS Browser = False. This removes the internet browsing service that allows users to bypass the MDS service.
4. Browser Policy Group > MDS Browser Use Separate Icon = True. This ensures a separate icon on the home screen for the MDS browser.
5. Service Exclusivity policy group> Allow Other Browser services = False. This will allow no other browser services except for the BlackBerry Browser to access the web.