This issue most frequently occurs when one of the following conditions is true. However, it may also occur in other scenarios:
- A journaling mailbox is deployed in the Exchange Server 2010 environment.
- A third-party email message archival system is used.
For more troubleshooting information, go to the following Microsoft TechNet website:
- Create a new mailbox database.
- Move the mailboxes to the new mailbox database.
- Delete the old mailbox database.
This workaround recovers the leaked database space. However, the new database may start leaking space. You have to apply the fix to prevent new leaks.