code: def init_app(self, app):
          
          self.init_config(app)
          if 'mail' not in app.extensions:
              Mail(app)
          if app.config.get('MAIL_SUPPRESS_SEND', False) or app.debug:
              email_dispatched.connect(print_email)
          app.extensions['invenio-mail'] = self
docs: Flask application initialization.
  
          The initialization will:
  
           * Set default values for the configuration variables.
           * Initialise the Flask mail extension.
           * Configure the extension to avoid the email sending in case of debug
             or ``MAIL_SUPPRESS_SEND`` config variable set. In this case, the
             email will be written in the stream configured in the extension.
  
          :param app: Flask application object.