[Exim] redirect email to external addresses

Hi,
I want to redirect email to external addresses.
I have a alias file, and if a local_part is inside, I want to redirect
email to the alias.
example :
abc : redirect@???
xyz : to.this@???

thus if, I got a mail for "abc@???", I want to send it to
"redirect@???"
But, until know, I'm unable to configure exim to do that.
Can someone help me?
Thanks
--
WIAME Jean-Robert <jrw AT ngi.be>
Institut National Geographique
BELGIUM