Mail.app Not Learning Junk Mail Anymore?

[polycat33]

I currently have my junk mail rerouted to the junk folder, after it seemed that mail had learned what was junk and what wasn't, mostly. However, each day I still get a lot of junk mail. Today, I clicked the junk button to mark an email as junk, and then the next time I checked my mail, I had a new email, delivered to my inbox, with the exact same subject line AND body of the email. That seems to me that the program is no longer "learning" what junk mail is. Does the learning part stop after I start rerouting into a junk folder? Is there any more powerful junk plugin I can get for mail that can catch all these obvious junk emails?