I have found that Zimbra's install of SpamAssassin hasn't been doing as good of a job as it used to. I have some custom rules set up, but I don't want to customize it too much because it becomes a pain to continuously update it on every upgrade.
I also had medicore results with MailScanner. Wasn't much better than Zimbra's built in.
What's everyone else using? How do you like it?
This is simply a poll, with any comments you have about past/current solutions you're using. I'd like to hear!