Exchange 2010 database space not being reclaimed quickly
We have seen an issue in our environment where deleted space is not being recovered very quickly. The database white space reports are generally very small, yet if we move all the mailboxes off the database, delete/recreate the empty database, and then move the mailboxes back, we can reclaim hundreds of GB. As an example, in a 700GB database, we cleaned it up and it ended up being 275GB.
We use Enterprise Vault and the problem is related to the fact that Exchange 2010 SP1 was not reclaiming the storage correctly. Microsoft has resolved this in Exchange 2010 Service Pack 2 RU1. (We were still running SP1 due to the difficulty in quickly applying service packs and updates in our environment.)
Bottom line is that you should get your E2K10 environment up to at least E2K10 SP2 RU1.
Symantec provides a good description of this issue in this article: Exchange 2010 Whitespace Reclamation
Microsoft KB 2621266 An Exchange Server 2010 database store grows unexpectedly large