Hmm. My first attempt to answer Jari's question seems to have vanished into
the ether.
Other people have already posted most of what I had there, and Ed Sabol's
explanation of why Resent- headers outrank others was quite good.
My only comment which I've not yet seen from anyone else is that, if you
truly want to make formail -r or formail -rt overlook Resent- headers to
figure out the return address, this does work (at least in 3.11pre7):
formail -I Resent- -rt
# or
formail -I Resent- -r # if you're not using the -t precedences