def _send(self, sender, to, subject, message, cc=None, bcc=None, attach=None, replyto=None):
        """
        Send a Letter (MESSAGE) from SENDER to TO, with the subject SUBJECT

        Arguments:
        - `sender`: unicode
        - `to`: unicode
        - `subject`: unicode
        - `message`: unicode
        - `cc`: str or [str]
        - `bcc`: str or [str]
        ` `replyto`: str

        Return: None
        Exceptions: None
        """
        self.mailer.send(sender, to, subject, plain=message, cc=cc, bcc=bcc, attach=attach, replyto=replyto)
        return