[exim] Retry rule of NDR based on error

Hi,

my exim server acts as gateway, some email is rejected as spam by the destination server and exim therefore creates a NDS (bounce) message.
Because a lot of the spam senders won't send with a legit sender address, exim continues trying to send the NDR even tough the destination rejects the email or the recipient does not exist.

I would like to let exim try only ONCE to deliver the NDR if it's because of previous spam rejection.

In my mind i thought of adding a special header to the NDR (like X-SPAM-ERROR:5.7.1) and if this header is set exim will drop the message after delivery error instead of freeze and retry delivery.

How could i achieve this or maybe there is another much easier way?

Thanks for all help,
Thomas