[exim] Rewriting From-Header

Hi list!

I'd like to rewrite the From-Header of the outgoing E-Mails.
So I added in the router:

headers_remove = From:
headers_add = From: ${acl_m_newfrom}

acl_m_newfrom was set in the rcpt-ACL.
Unfortunately the From-Header will be empty.

Can someone say me what I'm doing wrong?

Thanks
Luca Bertoncello
(lucabert@???)