I posted an answer to this question on Monday on the Webmail blog.  However, something is broken with the feedburner RSS feed on our site.

Anti-spam has been one of my areas of focus for several years, and something that I have enjoyed.  Recently though, spam fighting has gotten pushed to the side with all of the other things that I am responsible for.  It is painful to watch spam slip by the filters and I am definitely excited to have Mike T working on this project.

The first thing Mike is going to do is take our existing whitelist/blacklist functionality and push it up to the Postfix level, rather than the amavisd + spamassassin level.  This will ensure that system-wide rules don’t override individual user or domain rules.  The second thing he is going to do is give our customers the ability to whitelist/blacklist IP addresses, in addition to just sender email addresses.  Next, Mike will be building a system that makes "whitelist/blacklist/greylist/unknown" decisions based on aggregate whitelist/blacklist data, sending history, mail volumes and third party sender reputation databases.  This will be some really powerful stuff.  After that, he will do some work on the content filters behind this sender reputation system, possibly incorporating DSPAM which learns from the spam that each individual receives.