Need exim to rewrite Sender header

["Eric G. Miller" <egm2@jps.net>]

My ISP just changed their mailer, and they will no longer accept mail
that doesn't have a valid "Sender" header.  Since I have a home system
with no domain name, my Sender header reads $USER@$HOST.  What I'd like
exim to do is make the Sender header be the same as the From header for
any mail not being delivered locally.  I tried the header rewrite, but
it apparently doesn't work with the "smarthost" transport.
-- 

Eric G. Miller
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