[exim] Calling my own app from an ACL ???

Hi All...

I'm trying to figure out how, if it is possible, to use an application I
wrote to validate a recipient address in an ACL. After going through the
book and online, it seems that there is not a way for me to do this,
although it does seem that I can use pipe in the system filter.

I also saw that I can get an ACL to call a router, but I am confused about
how that works.

Does anyone know if it is possible to do this and if so what the trick is?

Thanks very much...