[Exim] Redirection to MS Exchange from exim on Linux

I installed exim on Linux Box as mail servler -- mail.xxx.com.
We also have NT which is running MS Exchange -- mail2.xxx.com.
Both mail servers are on the same domain -- xxx.com.

My setup is like this:
All emails go to users on linux box with exim. But some users
don't exist on linux, only on MS Exchange (NT box).

Is it possible to configure exim to get emails for users on linux
box and if they don't exist on Linux box (/etc/passwd), then
redirect the emails to MS Exchange on NT box? My question
relates to the redirection of unexistant users on Linux to MS Exchange.
I presume that configurations are supposed to be done with exim mta.
I couldn't find the information on this.

Any help would be greatly appreciated.

Slava