Ask HN: What anti-spam server based mail system do you recommend?

Hi all, my current anti-spam system (spamassassin) is simply not up to the task anymore so I am looking for suggestions on what to replace it with. My current Email platform is as follows: SMTP email server that receives email but immediately blocks mails to unknown inboxes (i.e. it's not a catch-all). The SMTP server runs all emails through SPAMC (the command line spamassassin tool) and then if not spam it goes into the correct mailbox in Microsoft Exchange, or if it is spam it goes to the postmaster mailbox. I have about 300+ aliases against 10 or so domain names. What I'm looking for is something that effectively traps spam and malware, and also has some sort of web interface where users can view/fwd the trapped spam. I am open to any and all solutions, but I do have to keep MS Exchange as the mailbox repository. Any ideas?