[Exim] old school exim 3.20: from rewrite based on to addres…

I no it sounds bad.. but I would like to rewrite the senders address
based on which user they were sending too!

I was hoping the following:

user@domain some_user@some_domain Ffr

translated too:

if user@domain exists anywhere in the headers, then the Ffr will be
changed to some_user@some_domain

Or does it really mean if user@domain exists in any of the Ffr headers,
then the Ffr will be rewritten to some_user@some_domain

That was all probably more for an educational exercise. Any tips on how
to rewrite the senders address based on the user they were sending too??

Regards,

ajt.