[exim] Envelope sender/from woes using smarthost

In the past, I have used mutt on robust (my main mail server) using the
envelope_from=yes option to mutt, which I think causes mutt to call exim with
the -f option so that the envelope from is the same as the headers from. That
was necessary because I have several email identities, and some lists will
ignore emails if the envelope and header from aren't both exactly right.

Now I am trying to set up a satellite system so that I can roam with my laptop
using offlineimap to sync mail, and exim to send. Mail is sent to a local
exim on the laptop, using the Debian smarthost setup, with robust as the
smarthost. I use PLAIN AUTH, and it seems to work fine, except for one thing:
the mails sent this way have the envelope from header set by the contents of
/etc/email-addresses on robust. How can I get the behavior I want (setting
the envelope sender from mutt on my satellite system)?

I checked the mailing list archives to no avail.

Thanks much,
Daniel