def _appendMessages(self, mbox, messages):
        results = []
        def append():
            for m in messages:
                d = mbox.appendMessage(m)
                d.addCallback(results.append)
                yield d
        d = task.cooperate(append()).whenDone()
        d.addCallback(lambda ignored: results)
        return d
Deliver the given messages one at a time.  Delivery is serialized to
dataset/ETHPy150Open kuri65536/python-for-android/python-modules/twisted/twisted/mail/test/test_mail.py/_AppendTestMixin._appendMessages