[Exim] Need help with REPLY_TO

HI all.

I just want to masquerade everything coming out from my MTA and have
the reply_to address set to another domain name. I have been playing
around with setting the reply_to variable under the transport section
but having no success. I don't have to fiddle with header rewriting,
do it? I just want to do this for outbound mail only.

local_deliver:
reply_to = "${local_part}@???"
...

Thanks for your help.

Chan