[exim] Forwarding inbound messages to 2 mail servers

My company is migrating from Sendmail to Scalix. We use Exim 4 as our
smtp mail gateway.

We plan to run both mail servers in parallel for a short period while
we make the transition.
I would like to have the Exim gateway server send copies of inbound
mail to BOTH mail servers ( Sendmail and Scalix). Also, I would like
to configure Exim to also send copies only for specify users.

How do I make this happen?
TIA

--
Regards,
Conrad Lawes