If you are moving mailboxes between servers in Exchange 2003 SP2 or Exchange 2007 and your clients are Outlook 2007, chances are you’ve already run into this problem before. The KB article 940012 documents this behavior for Exchange 2003 SP2 and a hotfix is available on the same page :
However, even after applying the hotfix on both the source and the target server of the Move Mailbox operation, you may still encounter the problem for mailboxes used with Outlook 2007. This happens because Outlook 2007 creates a search folder called Tracked Mail Processing at the same level as Top of Information Store in the mailbox folder hierarchy.
When the folders of the mailbox located on the source server are deleted (recursively, all the child folders are deleted from the root folder), usually the Top of Information Store is deleted first , which leaves the Tracked Mail Processing folder with and unknown folder id (FID) and therefore impossible to remove.
What the hotfix in KB article 940012 actually does is make the events 9533, 10001 and 10002 visible so that the administrators become aware that they are facing this problem. The administrator then has to apply one of the workarounds:
1. Move the mailbox back to the original mailbox store. This operation will fail but the disconnected object will be deleted.
2. Wait for the Maintenance to run on the database where the disconnected mailbox is located. This will remove the object.
If you do not wish to wait, you can speed up this process by setting the deletion settings for the mailboxes for 0 days (Keep deleted mailboxes for …days) and then schedule the maintenance to run sooner (by default it runs between 2:00 AM and 6:00 AM every day)