WC_Emails::backorder PHP Method

    public function backorder($args)
    {
        $args = wp_parse_args($args, array('product' => '', 'quantity' => '', 'order_id' => ''));
        extract($args);
        if (!$product || !$quantity || !($order = wc_get_order($order_id))) {
            return;
        }
        $subject = sprintf('[%s] %s', $this->get_blogname(), __('Product backorder', 'woocommerce'));
        $message = sprintf(__('%1$s units of %2$s have been backordered in order #%3$s.', 'woocommerce'), $quantity, html_entity_decode(strip_tags($product->get_formatted_name()), ENT_QUOTES, get_bloginfo('charset')), $order->get_order_number());
        wp_mail(apply_filters('woocommerce_email_recipient_backorder', get_option('woocommerce_stock_email_recipient'), $args), apply_filters('woocommerce_email_subject_backorder', $subject, $args), apply_filters('woocommerce_email_content_backorder', $message, $args), apply_filters('woocommerce_email_headers', '', 'backorder', $args), apply_filters('woocommerce_email_attachments', array(), 'backorder', $args));
    }