def esmtpAUTHMalformedChallenge(self, code=-1, resp=None):
        """
        Fail because the server sent a malformed authentication challenge.

        @param code: The server status code from the most recently received
            server message.
        @type code: L{int}

        @param resp: The server status response from the most recently received
            server message.
        @type resp: L{bytes}
        """
        self.sendError(AuthenticationError(501, b"Login failed because the "
            b"SMTP Server returned a malformed Authentication Challenge",
            self.log.str()))

        Fail because the server sent a malformed authentication challenge.

        @param code: The server status code from the most recently received
            server message.
        @type code: L{int}

        @param resp: The server status response from the most recently received
            server message.
        @type resp: L{bytes}
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/smtp.py