[exim] Blacklist lookup?

Lets say I have a list with the left part of a bunch of email addresses

a.user
another.user
and-so.on

and I want an ACL to reject any mail to a domain where the local-part is
not found in that list.

Is that doable?

Basically, I want to filter the garbage before the backend Exchange 2000
has to swallow it for the customer. Customer will not upgrade to
Exchange 2003 in the foreseeable future, since that version actually
_is_ clever enough to reject nonexistent mails *mumble mumble*


.