A mailbox cannot be deleted if it contains inferior hierarchical
names and has the mailFlagNoSelect attribute. On most
systems this is the case when the mailbox name references a
directory on the server, and that directory contains other
subdirectories or mailboxes. To remove the mailbox, you must first
delete any child mailboxes that exist.
If the mailbox that is deleted is the currently selected
mailbox, it will be automatically unselected and any messages
marked for deletion will be expunged before the mailbox is removed.
If the delete operation fails, the client will remain in an
unselected state until SelectMailbox method is called.
The special mailbox name INBOX is reserved, and cannot be
deleted.