I'm providing VPS services and I don't want my IP addresses spoiled by spammers. What I want to achieve here is to route all the outbound traffic to some sort of smtp proxy server which will just let other traffic go through while analysing email packages against spams.
I know there are some good open source spam filter solutions there like spamassassin but these filters will need a MTA in front of it such as postfix. But for the VPS, I can't do this. So can someone shed some light on it please?