function wpf_sync_shipping_email( $customer_data, $order ) {

    if ( ! $order->get_user_id() ) {
        $customer_data['user_email']    = $customer_data['shipping_email'];
        $customer_data['billing_email'] = $customer_data['shipping_email'];
    }

    return $customer_data;

}

add_filter( 'wpf_woocommerce_customer_data', 'wpf_sync_shipping_email', 10, 2 );