code: def mime_to_bytes(msg, header_len):
      
      fp = BytesIO()
      g = BytesGenerator(fp, maxheaderlen=header_len)
      g.flatten(msg)
      return fp.getvalue()
docs: Function to convert and email Message to flat string format
      :param msg: email.Message to be converted to string
      :param header_len: the msx length of the header per line
      :return: the byte string representation of the email message