Go to Tools -> Accounts, click New, and choose POP, or if you see the
Account Setup Assistant, choose "Configure Account Manually", and then
choose POP. Enter a name like "Spam Free Account" or something else
descriptive. Fill in your name and any address, real or fake, that you want
to direct junk to. The only other field you need to fill in is SMTP server,
which should be the same as your real account. Then click OK.
Now, in the Accounts window, click the News tab, and open the news server.
Under "E-mail account", change from your default account to the Spam Free
Account, and then click OK. Repeat for each news server, and then you're
done!