[exim] envelope-from - best practices

Hi,

i'm running the latest exim on a FreeBSD-box for a small number (ca.
5) of domains and users. All users are local system-users.

Recently i tried to subscribe to a mailing-list, which totally went
wrong, since the MLM tried to subscribe me with the envelope-from
address. So the from-header of the E-Mail stated '$SYSTEMUSER@
$DOMAIN', while the envelope-from stated something like 'prvs$HASH
$SYSTEMUSER@$HOST'. As you can see, i'm using BATV, because i've been
hit by backscatter in the past very badly. So even if i manage to
subscribe somehow to the list, i will never be able to post something
to it, because the envelope-from constantly changes due to BATV.

First a more general question: how do you handle envelope-from-
generation? Do you leave the default or do you rewrite it? If you
rewrite it, which address do you use?

Second: is it naive, to plain rewrite it to whatever is found in the
from-header? At least this would be a very logical approach to the
problem.

Third: are there any other side-effects, if envelope-from and from-
header are not matching? I assume no, because i haven't faced any
problems regarding this in the last couple of years.

Fourth: is BATV still feasible or should i consider something else?

Regards,

Alex