docs: def _setup_message(self):
          """Constructs the actual underlying message with provided values"""
          if self.content == 'html':
              self._message = MIMEMultipart('alternative')
              part = MIMEText(self.body, 'html', 'UTF-8')
          else:
              self._message = MIMEMultipart()
              part = MIMEText(self.body, 'plain', 'UTF-8')
          self._message.preamble = 'Multipart massage.\n'
          self._message.attach(part)
          self._message['From'] = self.sender
          self._message['To'] = COMMASPACE.join(self.to)
          if self.cc:
              self._message['Cc'] = COMMASPACE.join(self.cc)
          self._message['Date'] = formatdate(localtime=True)
          self._message['Subject'] = self.subject
          for part in self._parts:
              self._message.attach(part)