[exim] selectively routing outgoing traffic based on domain

Hello list

I'm looking for a method of sending outgoing mail, which, if destined for a
particular domain (let's say aol.com), gets routed through
some.smarthost.ip.address whereas the rest of it gets delivered via DNS as
normal. There are many ways in the documentation showing routing inbound
examples, but nothing I've seen so far showing an example outbound quite like
this. Can anyone help?

thanks
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