[Exim] no rewriting for local mails

Hi!

I saw this question in the mailing-list archive a long time ago. But I can't
see an answer. Is it possible to configure exim to rewrite the sender and
reply-address only for outgoing mails and not for intranet-mails?
There are so many possbilities to configure exim but I still haven' t found
the right way.

Thanks....Thomas