Training Apple Mail to recognize junk email

By default, Apple Mail will mark messages it suspects are junk, but leaves the messages in the Inbox. In order to improve the success rate, you should train Apple Mail's junk filter filter by marking unrecognized junk mails as you receive them in your inbox.

To mark an email:

1. Click once on the message so that it is highlighted in the Inbox list.
2. Click the Junk Mail icon in the toolbar.
3. If a legitimate email is wrongly labeled as junk, simply repeat this process to unmark it.

Customizing junk mail actions

After a reasonable amount of time, you may wish to turn off Training Mode and configure Apple Mail to move junk mails to a separate Junk folder upon detection.

To move junk mail to the Junk folder:

1. In Apple Mail, go to Mail menu --> Preferences.
2. Click on Junk Mail.  
3. Place a bullet in the box which says "Move it to the Junk mailbox (Automatic)".
4. Make sure all checkboxes in the window are checked, if not already.
5. Close the Mail Preferences window.

Since no junk mail filter is 100% accurate, it is your responsibility to check your Junk folder every few days to make sure no legitimate email has been moved there, and to clean it out periodically to conserve space.