Rewriting FROM, TO and CC

[Ignacio]

Hello,

I would like to rewrite FROM and CC headers. There is an application that
connects to a postfix smtp server and it sends an e-mail like this:
FROM: user1@domain
TO: user2@domain;user3@domain

And that e-mail is relayed to another e-mail server. I would like the
relayed e-mail to be something like:
FROM: genericuser@domain
TO: user2@domain;user3@domain
CC: user1@domain

Changing the FROM field is an easy task, but I don't know how to add
user1@domain as a CC (It is a must to be CC, BCC is not an option)

Thank you very much.

Regards.