I keep getting spam in Apple Mail from different sources. It likely is actually coming from the same source but each incoming from address is different. I mark each item as spam using SpamSieve and I guess that blocks it should I ever see mail from that source but I'll get a dozen emails a day each with a different from line.
Let me explain how SpamSieve works, so there is no confusion.
When you first install SpamSieve you train it by showing it examples of lots of typical e-mail messages you have received from legitimate sources, and lots of typical spam messages you have received from spam sources.
SpamSieve looks at EVERY SINGLE word in an e-mail message and ranks it for how commonly that word shows up in spam that you have received in the past. Words, like the address of a friend who appears in your address book, are given a very high score for being legitimate. Words that commonly appear only in spam messages are given a very high score for being spam.
In a short period of time, SpamSieve has ranked many thousands of words. Once SpamSieve has ranked all of those words, it can analyze incoming e-mail messages word by word and use artificial intelligence to figure out the probability that a message is spam. This AI is shockingly accurate when SpamSieve is working properly.
However, you must install, train, and maintain SpamSieve precisely as its instructions dictate. This isn't at all hard to do, but if you fail to do it properly SpamSieve won't work well for you. Fortunately, C-Command is excellent at assisting you with this if you need them.