Spam, the junk that now makes up more than 80% of email, is a problem that's only getting worse. Luckily, you, along with Mail's advanced spam filters, can make it better—at least for your email accounts.
You'll see the effects of Mail's spam filter the first time you check your mail: A certain swath of message titles appears in color. These are the messages that Mail considers junk.
Out of the box, Mail doesn't apply its spam-targeting features to people whose addresses are in your address book, to people you've emailed recently, or to messages sent to you by name rather than just by email address. You can adjust these settings in Mail→Preferences→-Junk Mail tab.
During your first couple of weeks with Mail, your job is to supervise Mail's coloring job. That is, if you get spam that Mail misses, click the message and then click the Junk button at the top of its window (identified in Figure 20-3), or the Junk icon on the toolbar. On the other hand, if Mail flags legitimate mail as spam, slap it gently on the wrist by clicking the Not Junk button. Over time, Mail gets better and better at filtering your mail; it even does surprisingly well against the new breed of image-only spam.
The trouble with this so-called Training mode is that you're still left with the task of trashing the spam yourself, saving you no time whatsoever.
Once Mail has perfected its filtering skills to your satisfaction, though, open Mail's preferences, click Junk ...