Moving a message to a PST is considered a Hard Delete.
You must enable Hard Delete support on the BES for the BES to see these deletes.
To enable hard delete support do the following:
-Open BlackBerry Manager.
-In the Explorer view, click Server.
-On the Server Configuration tab, click Edit Properties, then click Messaging.
-For the Hard Deletes Reconciliation option, choose True from the drop-down menu.
-Restart the BlackBerry Enterprise Server services.
See RIM KB04853 for more details: http://www.blackberry.com/btsc/searc...200%2033127421
Hard Delete Reconciliation has a customizeable limitation. The default is the last 100 messages for each user.
Hard Delete Reconciliation will allow the BES to reconcile moves to PST and Hard Deletes (skipping Deleted Items, or emptying Delete Items)