[exim] Help regarding Incoming & outgoing mails

hi to all,

i am new user to exim and need a detailed guidance of Exim.

As of now..
my question is..

i have 3 users abc, def & ghi
i want that all the incoming & outgoing mails of def & ghi will also be
copied to abc.
and def & ghi should not be aware of this.
could u pls tell me that for this where i have to make the changes and what
r the entries required??

Pls help me soon..

Thanks & Regards