A couple years ago I described how to reconcile hard deletes for BES 4.x, and with BES 5.0 and the new web-based administration tool the process has changed a little bit. In an Outlook/Exchange environment you can Hard Delete selected objects by pressing shift+delete, bypassing the Deleted Items folder and immediately deleting the item.
Enabling Hard Delete Reconciliation
Log into the BAS and from the Servers and Components drill down to BlackBerry Solution topology > BlackBerry Domain > Component View > Email > YourServer_EMAIL. Click on YourServer_EMAIL and you'll be presented with the configuration screen for the Messaging Agent.
Click the Messaging tab, and click the Edit instance link.
Change Hard deletes reconciliation to True and click Save All to apply the changes. That's it, no need to restart the service.