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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def post_to_url(self, value):
 """An Inbound Parse URL to send a copy of your email. If defined, a copy of your email and its spam report will be sent here. :param value: An Inbound Parse URL to send a copy of your email. If defined, a copy of your email and its spam report will be sent here. :type value: string """

        if isinstance(value, SpamUrl):
            self._post_to_url = value
        else:
            self._post_to_url = SpamUrl(value)