We had an issue where serveral users had reached their mailbox limits but where reporting that they had manually cleaned their mailboxes. What we eventually found was that users had somehow dragged messages into the root of the Outlook hierarchy 'Mailbox - User Name.' We found this by searching for all messages larger than 1 KB (Advanced Search) and seeing that they resided in a folder named 'Top of Information Store.' Besides searching and deleting the messages (from within the search box) there is another way to see what messages exist in the 'Top of Information Store.'
1.Find mbdvu32.exe in the Tools\ExAllTools\MDBVU32 directory on the Exchange CD
2. Exedute mbdvu32.exe
3. Click OK to clear the first window that pops up.
4. Make sure that the correct profile is slected in the 'Choose Profile' windows
5. Click on the MDB menu option.
6. Click on the OpenMessageStore option.
7. Make sure that "Mailbox- [user's full name]" is selected and click on Open.
8. Click on the MDB menu option again.
9. Click Open Root Folder.
10. In the Child Folders box - double click on "Top of Information Store".
11. In the window to the right, titled 'Messages in Folder' you will be see all the messages that the user has dragged into the top of the Outlook hierarchy.
Thanks goes out to the people at MS Exchange Blog and their article below. It actually shows how to fix OOF problems using the same utility.
http://hellomate.typepad.com/exchange/2003/10/when_oof_doesnt.html
