'IMAPrev1 extension THREAD command.
(type, [data]) = <instance>.thread(threading_algorithm, charset, search_criteria, ...)'

def thread(self, threading_algorithm, charset, *search_criteria):

    name = 'THREAD'
    (typ, dat) = self._simple_command(name, threading_algorithm, charset, *search_criteria)
    return self._untagged_response(typ, dat, name)
