This article refers to the Barracuda ArchiveOne Enterprise or Express, and Microsoft Exchange Server 2010.
In Exchange 2010, Microsoft found that database space was not being reclaimed in several scenarios where items are hard deleted once the item is purged from the store. This includes archiving scenarios where items are bulk deleted based on date, and stubbing scenarios where email attachments are deleted.
Exchange 2010 attempts to clean up the row for a deleted item within a couple of minutes of the item being hard deleted. However, cleanup fails if another process has open references to the item. Outstanding references on deleted messages are particularly common in journaling mailboxes, or when third-party archival software is used. The vast majority of customers who experienced this behavior have associated it with one of the aforementioned scenarios. However, technically any client can hold an open reference and prevent an item from being cleaned up.
For details on getting an accurate whitespace figure and Microsoft's recommendations for reclaiming whitespace, refer to the Microsoft Exchange Team Blog article Database Maintenance in Exchange 2010.
After you have followed Microsoft's recommendations to resolve this issue, verify that whitespace is reclaimed as expected.