Add a template tag for the email of the person who submitted the booking request.

email-template-tag-for-rtb.php

<?php
/**
 * Plugin Name: Email Template Tag for Restaurant Reservations
 * Plugin URI: http://themeofthecrop.com
 * Description: Add a template tag for the email of the person who submitted the booking request.
 * Version: 0.0.1
 * Author: Theme of the Crop
 * Author URI: http://themeofthecrop.com
 * License:     GNU General Public License v2.0 or later
 * License URI: http://www.gnu.org/licenses/gpl-2.0.html
 *
 * This program is free software; you can redistribute it and/or modify it under the terms of the GNU
 * General Public License as published by the Free Software Foundation; either version 2 of the License,
 * or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without
 * even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 *
 * You should have received a copy of the GNU General Public License along with this program; if not, write
 * to the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 */
if ( ! defined( 'ABSPATH' ) )
	exit;


/**
 * Add the email template tag
 */
if ( !function_exists( 'rtb_add_email_template_tag' ) ) {
add_filter( 'rtb_notification_template_tags', 'rtb_add_email_template_tag', 10, 2 );
function rtb_add_email_template_tag( $template_tags, $notification ) {

	$template_tags['{user_email}'] = $notification->booking->email;

	return $template_tags;
}
} // endif;