code: def fetch_plaintext(self, msg_nums):
          
          if not msg_nums:
              raise Exception("Invalid Message Number!")
  
          return self.__imap_fetch_content_type(msg_nums, self.PLAIN)
docs: Given a message number that we found with imap_search,
          get the text/plain content.
          @Params
          msg_nums - message number to get message for
          @Returns
          Plaintext content of message matched by message number