docs: def serialize_email_messages(messages: List[EmailMessage]):
      """Serialize EmailMessages to be passed as task argument.
  
      Pickle is used because serializing an EmailMessage to json can be a bit
      tricky and would probably break if Django modifies the structure of the
      object in the future.
      """
      return [
          base64.b64encode(zlib.compress(pickle.dumps(m, protocol=4))).decode()
          for m in messages
      ]