[Exim] Mixed Headers Rewrite..

hi all,

    Thanks for the help in the mailbomb problem, now that have subscribe to
exim user list, I would like to ask if anybody knows how to rewrite
headers for the follwing case (as I could'nt find anyway in the
spec.txt)

if envelope To field = "foobar@???"

then rewrite the "To:" = "foobar@???

this is needed for some strange filtering setup on the local setup, I
don't want to modify the envelope but want to modify only To: depending
on enevolpe.

TIA

ewiz