To enjoy the benefits of Yahoo! SpamGuard Plus, first make sure it's turned on:
Sign in to your Business Mail account at http://mail.yourdomain.com (be sure to replace "yourdomain.com" with the domain name associated with your account).
Click "Options" in the upper-right corner of the page, then choose "Mail Options" from the pull-down menu.

On the left side of the page, select the "Spam" option.

On the Spam page, a check in front of the "Automatically send suspected spam to my Spam folder" option indicates that SpamGuard is enabled.

To turn SpamGuard off, click to deselect this option.

Click the "Save Changes" button to save your settings.

Remember: The more you mark junk messages as spam, the better SpamGuard Plus works for you. So whenever you receive a spam message, be sure to click the "Spam" button above your Inbox or in the Spam column beside the message. This will train your Spamguard Plus filter and help keep you protected from spam!