This is so amazing I just have to report it. We have an alias address from an organization that is just over-run with spam. In fact I think someone is forging their headers, but that is a whole other story.
I routed that alias address to my yahoo mail address which I collect using Power Mail. I put a filter right before the Spam Sieve filter for mail from that address to go to its own folder, but I did NOT check "Don't apply subsequent filters.." which means that it goes through Spam Sieve before it goes to the folder. It is working so perfectly it is hard to believe.. legitimate messages go to the folder and spam messages are caught and put in the Spam folder. I bought a separate license for my husband to use on his laptop with Apple Mail and for the first time in his e-mail experience he is experiencing spam free e-mail. I love PowerMail filters much better than Apple Mail ones which is why of course I use PowerMail ... but my husband is used to Apple Mail and with Spam Sieve he now has a good experience. -- Barbara Needham