It's happened to me twice. I created a second set of subfolders in my Inbox. I set up about 20 rules to point new mail into the various subfolders.

In the midst of reviewing mail, my account hangs which seems to happen frequently, even though this is a brand new computer. I am in the midst (in addition to setting up new subfolders) to converting mail from Entourage files to Outlook files and it's been nothing but problems.

Anyway, I do a force quit and when I reopen Outlook. All of the subfolders are gone.

When I go to the Outlook file on my hard drive, there are only two folders. They are the two email addresses that I have pointing to my default address. My default email address does not have it's own folder.