Save billing e-mail after successful order in Woocommerce

Here is a simple snippet that I always forget, how to save an e-mail address after order processing:

function checkout_processed_callback()
{
	global $wpdb;

	$wpdb->insert(
		'newsletter_table', 
		array(
			'email' => $_POST['billing_email']
		),
		array('%s')
	);
}

add_action( 'woocommerce_checkout_order_processed', 'checkout_processed_callback');