``` function user_role_update( $user_id, $new_role ) { $site_url = get_bloginfo('wpurl'); $user_info = get_userdata( $user_id ); $to = $user_info->user_email; $subject = "Role changed: ".$site_url.""; $message = "Hello " .$user_info->display_name . " 亲，您在".$site_url.", 角色已经变为 " . $new_role; wp_mail($to, $subject, $message); } add_action( 'set_user_role', 'user_role_update', 10, 2); ```