I lost my junk mail icon – how do I get it back to teach my inbox what is junk?
Mail menu > Preferences > Junk Mail
Set it to automatically Move it to the Junk mailbox, as opposed to what used to be called Training mode, which is now, in Leopard the Mark it as junk mail, but leave it in my Inbox setting.
But before you do, I would suggest leaving it in Training mode for a bit, and clicking the Junk/Not Junk button. In fact, one will initially need to train Apple Mail to recognize legit mail — newsletters and such — by clicking Not Junk.
I’ve always said a month, but that’s an arbitrary guess on my part, and is contingent on someone being vigilant about clicking the Junk/Not Junk button. Stay in Training mode until you are confident that it’s catching junk mail correctly by marking junk mail brown, and leaving non-junk along.
Make sure that you add any trusted correspondents to your address book (Message menu > Add Sender to Address Book (⌘⇧Y)) to prevent them from being mis-identified as spam.
Gmail, if you use it, and you should be using it, will catch most of the spam most of the time, but that’s how you deal with the rest.