[exim] Sending by smarthost depending on From: address?

Hi folks.

I'm using exim4 on ubuntu edgy. My objective is to only use my gmail smarthost when sending from my user1@??? and user2@??? accounts, but when i send from my registered domain account, not to route to the smarthost. I've googled for the past 2 days, and haven't found anything pertinent. Can someone point me in the right direction in the docs, or let me know if this is not possible?

Thanks
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Glen Barber