I have a very simple Exim configuration that's just forwarding all mail to a set of destination addresses. When immediate delivery to an address fails, the message is added to the queue (and then processed by the retry rules). I want to change this so that if immediately delivery fails, the message is :blackhole:d. (It's ok if a bounce is generated instead, as I'll just redirect the bounce to the :blackhole:).
This needs to occur for temporary failures (i.e. 4xx) as well as permanent (i.e. 5xx) ones.
I understand that this means that if delivery can't be done immediately the message will be permanently and irretrievably lost. In this particular context, that isn't a problem.
Reading over this, it sounds suspiciously like "how can I improve my spamming Exim server". That really isn't what this is for, and if you can figure out a way I can prove that, I'm happy to do so!