[Exim] rewrite & forwarding question

Hello :-)

I have a local mail domain & isp's mail domain.
all addresses rewrited (something@localdomain to something@???)
For example my mailbox is user
but I also whant to recieve & send messages as user2 from the same acount
If message consist in it header "sometext" it must be sent from user2@localdomain and rewrited to user2@???
Also I need that messages recieved from some addresses copying to multiple users. How to realise that?
Please tell me what to use and to read about that?

Best Reagrds,
Andrew