JSI Tip 5233. Outlook Express error: 'Your folder could not be deleted: the IMAP server refused to delete it'?

When you try to delete an IMAP (Internet Message Access Protocol) folder, Outlook Express issues:

Your folder could not be deleted: the IMAP server refused to delete it.

If you press Details, you receive:

The specified mailbox has inferiors and cannot be deleted.

You must delete any sub-folders before you delete an IMAP folder.