Entourage 2004 and SpamSieve
SpamSieve is fully compatible with Entourage 2004, and that combination in fact works better than SpamSieve and Entourage v.X. The reason is that Entourage 2004 lets you uncheck “Do not apply other rules to messages that meet these criteria” for AppleScript rules. This means that spam messages from Exchange, Hotmail, and IMAP accounts can now be moved to the spam folder (by setting up a second rule), even though Entourage cannot move these messages via AppleScript.