. Add to /etc/apt/sources.list:

deb www.backports.org/debian stable spamassassin

. apt-get update

. Install the following packages: spamc spamassassin

These brought in the following additional dependancies: debhelper
debconf
debconf-utils
gettext-el
gettext
intltool-debian
po-debconf
debhelper

Put the following in scenari/include.send.header (This traps any messages that Spamassassin has flagged as spam, and replies to the sender, asking for confirmation in order to send the message): match(header->X-Spam-Flag,/YES/) smtp -> request_auth

Put the following in /etc/spamassassin/local.cf:

rewrite_subject 1

Put the following in /etc/default/spamassassin:
ENABLED=1

At the moment spamassassin is doing baysean and auto-white listing, I am not sure if this is such a good idea, but we'll see how it goes. It is also doing RBL checking against the more liberal RBLs, which I think is fine, since the RBL checks only modify scores, not completely block. I actually think that the spam score should be brought down to 6iething like 3 instead of 5 because people have the opportunity to confirm their messages, if they are spam.