[Exim] routing to selective domains

I'd like to route my outgoing mail to different domains depending on the
address.

I'm hoping to be able to send all mail through 'exchange.something.com'
unless the address matches /^.*\.chunky\.something\.com$/.

I'm guessing that I'd be using multiple routers -- one of them looking for
the 'chunky' domain and the others falling through to the default smarthost
router. I'm a little uncertain as to how I'd accomplish this, though.

This seems like a simple enough configuration so I apologize if it's been
answered before.

Thanks for your help.

-adrian-