A mailbox cannot be deleted if it contains inferior hierarchical
names and has the IMAP_FLAG_NOSELECT 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 either the ExamineMailbox or SelectMailbox method
is called.
The special mailbox name INBOX is reserved, and cannot be
deleted.