Converts Postmark message API field names to their corresponding
        :class:`Message` attribute names.

        :param message: Postmark message data, with API fields using Postmark
            API names.
        :type message: `dict`

def _convert_postmark_to_native(cls, message):
        '''Converts Postmark message API field names to their corresponding
        :class:`Message` attribute names.

        :param message: Postmark message data, with API fields using Postmark
            API names.
        :type message: `dict`
        '''
        d = {}
        for dest, src in cls._fields.items():
            if src in message:
                d[dest] = message[src]
        return d