If you want to handle the three cases individually using your implementation, you would have to make another function call, rather than just the one

You don't, although it is perhaps quite awkard:

    message.is_blatant_spam  # true if blatant spam
    message.is_spam and not message.is_blatant_spam  # true if possibly spam
    not message.is_spam  # true if not spam

    @property
    def is_possibly_spam(self) -> bool:
       return self.is_spam and not self.is_blatant_spam