I'd like to do that, but greylisting is typically done at the SMTP level -- before the messages are anywhere close to SpamAssassin. Can I ask how you're accomplishing this?

You can run SpamAssassin at SMTP time in the DATA phase. At least, you can with both Exim and Postfix. I assume other MTA's support that too. You can run Greylisting at the same stage after SpamAssassin has been run and before the message has been accepted.

Have a look at assp, complex set-up but very powerful.

http://sourceforge.net/projects/assp/

Thanks, the web interface for that looks pretty nice but it'd take too much to move our mail systems to that.