def extract_text_body(parsed_email):
     """
     Extract email message content of type "text/plain" from a parsed email
     Parameters
     ----------
     parsed_email: email.message.Message, required
         The parsed email as returned by download_email
     Returns
     -------
     string
         string containing text/plain email body decoded with according to the Content-Transfer-Encoding header
         and then according to content charset.
     None
         No content of type "text/plain" is found.
     """
     text_content = None
     text_charset = None
     if parsed_email.is_multipart():
         # Walk over message parts of this multipart email.
         for part in parsed_email.walk():
             content_type = part.get_content_type()
             content_disposition = str(part.get_content_disposition())
             if content_type == 'text/plain' and 'attachment' not in content_disposition:
                 text_content = part.get_payload(decode=True)
                 text_charset = part.get_content_charset()
                 break
     else:
         text_content = parsed_email.get_payload(decode=True)
         text_charset = parsed_email.get_content_charset()

     if text_content and text_charset:
         return text_content.decode(text_charset)
     return