If you're getting a lot of spam in your Business Email account, check the following three things:
Is your email address POP-only?
POP-only email addresses cannot use Yahoo!'s SpamGuard Plus feature, which automatically filters junk mail into your Bulk or Spam folder. This means that you'll get all messages sent to your inbox, even those we suspect as spam. The POP email client you access your mail with may include spam filtering (consult the POP client's help files). You may also choose to delete the email address, then recreate it with Yahoo! and POP access to take advantage of SpamGuard Plus.
Is your catch-all activated?
Because a catch-all mailbox collects everything sent to your domain, it can accumulate spam. If you find you're receiving too much junk mail, you may decide to turn off your catch-all.
If you still have questions about spam, visit the Yahoo! Security Center.