[Exim] passing mail from one server to the next for spam ass…

I mentioned this earlier, in a round about way. I'm intrested in setting
the current mail server (which is being replaced) to process mail using
spamassassin before passing the mail onto the webmail server. We get too
much spam at this site, and I am wondering if this is a wise solution.

currently we use for RBL checking:

rbl_domains = rbl.maps.vix.com/reject :relays.mail-abuse.org/reject :
        relays.ordb.org/reject : inputs.orbz.org/reject

and finding that to be working, but not enough.