exim - spamassassin? - msexchange

[Michael Kahle <michael.kahle@scc-wi.com>]

I would like to setup a intermediary mail server that will filter email
coming in for spam and then reroute the "good" mail to my msexchange server.
Any suggestions on what I should use to do this?

I am currently thinking that I need to use exim as my mta and spamassassin
as my filtering program.  Does this sound like a good approach?  What
problems should I expect up front so that I can perhaps account for these
before I change over?  Is there a system that would allow users to send an
email to say nospam@mydomain.com and it could automatically process this
mail as spam and prevent future delivery?

Thanks for your time and opinions.

Michael