code: def print_email(message, app):
      
      invenio_mail = app.extensions['invenio-mail']
      with invenio_mail._lock:
          invenio_mail.stream.write(
              '{0}\n{1}\n'.format(message.as_string(), '-' * 79))
          invenio_mail.stream.flush()
docs: Print mail to stream.
  
      Signal handler for email_dispatched signal. Prints by default the output
      to the stream specified in the constructor of InvenioMail.
  
      :param message: Message object.
      :param app: Flask application object.