Ok, thank you. I have one question about the hook you’ve pointed out. Is there a way to access the order object/order id inside of it?
Example:
add_filter( 'woocommerce_email_recipient_sab_simple_invoice', 'your_email_recipient_filter_function', 10, 3);
function your_email_recipient_filter_function($recipient, $object, $email) {
$order = new WC_Order( $object ); // create new order object
$rechnung_email = $order->get_meta( '_billing_email_rechnung', true );
if ($rechnung_email) {
$recipient = $rechnung_email;
}
return $recipient;
}