Spam, the junk that now makes up more than 80 percent 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: Certain message titles appear in brown. 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 Contacts, 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 the Mail→Preferences→Junk Mail tab.
During your first couple of weeks with Mail, your job is to supervise Mail’s work. That is, if you get spam that Mail misses, click the message, and then click the Junk button 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.