[exim] Splitting the stream

Hi All,

I have a gateway running Exim in a datacentre (well, RedBus actually)

We have 2 sites with a mail server at each
(One Exim and one Exchange - don't ask!)

What might the best exim tool be to split the emails between the sites.

The addresses are fairly static so I can easily have a file on the
gateway with each user and their destination server.

We are currently accepting all emails on the final exim box and
forwarding those that need it to the other site!

TIA

Simon