[Exim] help needed

Hello again,

I am trying to do the following, is it possible to do with exim 3.3x?

I have a mail server A which handles large amounts of email traffic, and a
second mail server B ( virus scanning ). All domains are set to be delivered
to A, and all mail is sent out through A.

I wish to pass mail for certain domains (that are in a db file) on to mail
server B ( to be scanned) which then will pass the mail back to A (smart
hosting i assume) on which it would be stored/Sent on to the real world ( i
guess this conditional bit could be done through working on and compairing
headers at differant stages).
The bit i am having problems with at the moment is the sending of mail onwards
from A to B,mainly because exim see's the domain as a local domain (which it
is) and so it gets passed on to the directors (rather than routers) and
because of this i cant use the domainlist option (as far as i can tell).

Is it possible to do this, would it be considered as very messy? any better
solutions (mail scanning can not take place on A since the overheads incured
would be concidered too high)


Antony