The content(s) of the email

        :param contents: The content(s) of the email
        :type contents: Content, list(Content)

def content(self, contents):
        """The content(s) of the email

        :param contents: The content(s) of the email
        :type contents: Content, list(Content)
        """
        if isinstance(contents, list):
            for c in contents:
                self.add_content(c)
        else:
            self.add_content(contents)