[exim] Incoming Mails Issue..

hi to all...

i am new to Exim...and need ur suggestions ..

i have someusers like abc, def & ghi

i want that all the incoming mails of def & ghi will also be copied to abc
they all are from same domain mydom.com

the users should not be aware of this forwarding

i have an idea that it should be done by making entried in /etc/aliases

even i do so..

def: abc,def
ghi: abc,ghi

but its not working??
how can i do this on exim??

Pls help..!

Thanks & Regards
Keenlearner