The reply to email address

        :param value: The reply to email address
        :type value: ReplyTo, str, tuple

def reply_to(self, value):
        """The reply to email address

        :param value: The reply to email address
        :type value: ReplyTo, str, tuple
        """
        if isinstance(value, str):
            value = ReplyTo(value, None)
        if isinstance(value, tuple):
            value = ReplyTo(value[0], value[1])
        self._reply_to = value