[exim] IP Filtering Per Domain

We have a virtual mail system setup with over a hundred domains, some
of which want spam filtering and some of which do not. Spam filtering
is outsourced to Postini, and is working beautifully for us.

Except for a couple domains. Some spammers are mailing directly to the
mail server, bypassing the Postini filter servers. I need to figure
out how to reject/ignore the email that does not pass through the
Postini filters, on a per-domain basis (since not all domains want
filtering).

I can either block by IP (allow only mail from the Postini IPs), or by
header (dump all mail that does not have Postini headers), but
whatever I do needs to be done per domain. I know how to filter for
ALL the mail, but I'm hazy on how to properly impliment this on a per
domain basis.

Exim 3.34.

If there's any info you need that I'm skipping, let me know. If I'm
being a dufus, and just not seeing the right spot in the docs, point
it out. :-)
--
Myrddin Emrys
Technical Support
Dotnet Internet Services
888-228-4665 or 924-0593