[exim] How to avoid generating backscatter?

Hello, hope someone can help with this hypothetical (at the moment)
situation ...

- spammer sends email to userA@domainA
- domainA fails to detect that it is spam
- userA has set up forwarding to userB@domainB
- domainA attempts to forward email to userB@domainB
- domainB detects that it is spam, and rejects it (5xx)
- domainA sees 5xx, generates NDR, attempts to send it to ... oops, you
guessed, forged sender.

Is there any way for domainA to prevent the generation, or at least the
transmission, of the NDR? (Other than improving its spam detection
rates!!)

For bonus points, can domainA hang on to the original email and/or the NDR
(eg by freezing it/them), for later inspection?

Marks will be deducted for mentioning SPF ;-)

TIA,
Richard Hall