'Stores all unread messages.
If the backend has yet to be iterated, previously stored messages will
be stored again. Otherwise, only messages added after the last
iteration will be stored.'

def update(self, response):

    self._prepare_messages(self._queued_messages)
    if self.used:
        return self._store(self._queued_messages, response)
    elif self.added_new:
        messages = (self._loaded_messages + self._queued_messages)
        return self._store(messages, response)
