[exim] route local user through another smtp server

Hi,

Can you tell me how to route only some local user's mail, let's say user
"catalin", through another smpt server which accepts relaying from local
server, and the rest of the users to keep sending mail using local exim
email server?

I tried something like this:

catalin_router:
    driver = redirect
    senders = catalin@localhost
    transport = remote_smtp
    route_list = * relay_server's_ip

in "begin routers" section and doesn't work