[exim] Syntax errors in exim filters

Hej,

we have a bunch of customers over here that are allowed to write their
own exim filters, and as you allready may have guessed that causes lots
of troubles. I am especially annoyed that syntax errors in their filters
result in delivery defers, as their mails end up in my incoming server
queues until they get bounced after 4 days.
I've searched for a way to turn these errors into "permanent" ones - so
the mails get bounced quickly - but I didn't came to a solution. Am I
missing something, or is this just not possible? (for not-too-weird
values of "possible")

It would also be okay if I could verify exim filters at SMTP time, (so
others queue these mails for me ;o) but running arbitrary exim filters
during address verification (or after data) doesn't seem to be a very
reasonable thing.

I'm looking for a quick solution until I've implemented an exim filter
syntax check into the provisioning system (maybe tomorrow I'll find the
time...) and until the faulty filters got corrected, (which may take
even more time) but a more general approached may be worthwile. How
about yet another "specific error" in retry rules? As this is a
*routing* error, is this possible at all?


Thanks for your time,
daniel