ASSP

It doesn't really fit our architecture, and I'm not seeing any benefits it provides over SpamAssassin+ClamAV+Procmail...but maybe I'm missing something?

We do have some significant upgrades planned for the mail processing tool chain in the next few weeks, but adding a mail proxy is not one of them. I'm not a fan of mail proxies, in general. They steal information that Postfix and policy daemons hooked cleanly into Postfix could have used. Our plan is to integrate one of the policy daemons for Postfix to add greylisting, and a few additional "quick fail" spam tests (like SPF). This will reduce the load of SpamAssassin and ClamAV by a probably large amount--it might even reduce spam and viruses, though current SpamAssassin is remarkably good at spam detection (only about 0.2% of my spam makes it to my mailbox, and I haven't even trained the bayesian filter).