[Exim] domain aliases

Hi,

What's the best way to setup domain aliases so that email
to addresses at site2.com (eg, roger@???) automatically
get sent to the same local part at site1.com (eg roger@???)..

I have a text file listing:
original-domain, alias-domain
that i'm trying to get Exim to use..

Has anyone done this already?

Thanks,
Adrian.

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