Just installed SpamAssassin and modified the mx server, to hopefully stop some spam. I've found this tutorial and it has helped me a bit to configure everything. 100+ Spam mails/Day are definetely too much, so if everything works fine, it will reduce all the spam down to 20%. I mean: I've set up a little ruleset in theBat to store all flagged mails in a junk folder and mark them as read.
It's monday ;)
*note: the mx stuff seems to work and currently I get only 20 spam mails, which means a reduction of ~80% and spamassassin does the rest. Only 1-3 Spam Mails/day, which is quite cool :) *