Your Yahoo! Business Email account comes equipped with a feature called the SpamGuard Plus which is designed to automatically catch unsolicited messages and route them to your Spam folder.
SpamGuard is tailored to your individual preference, and you train it to learn what is spam and what is not every time you mark an email as Spam (or an email incorrectly routed to the Spam folder as Not Spam).
You can set also up filters to redirect messages.
Note: This feature is available only to those users with Webmail and POP access to their mailboxes, but not for POP only mailboxes.