def construct_message(self, email=None):
        """ construct the email message """
        # add subject, from and to
        self.multipart['Subject'] = self.subject
        self.multipart['From'] = self.config['EMAIL']
        self.multipart['Date'] = formatdate(localtime=True)
        if email is None and self.send_as_one:
            self.multipart['To'] = ", ".join(self.addresses)
        elif email is not None and self.send_as_one is False:
            self.multipart['To'] = email
        # add ccs
        if self.ccs is not None and self.ccs:
            self.multipart['Cc'] = ", ".join(self.ccs)
        # add html and text body
        html = MIMEText(self.html, 'html')
        alt_text = MIMEText(self.text, 'plain')
        self.multipart.attach(html)
        self.multipart.attach(alt_text)
        for file in self.files:
            self.multipart.attach(file)
construct the email message