SpamAssassin is available for you to turn on or off in the control panel of your PHP and Java JSP hosting. When enabled it will mark spam email coming in with {Spam?} in front of the subject line. This makes it very easy to filter using your email client.
If your control panel is a cPanel, then you also have the option of utilizing the Box Trapper. This is a very nice feature that blocks about 95% of all spam. It protects your inbox from spam by forcing all people not on your white list to reply to a verification email before they can send mail to you.
You can control the white and black lists by adding emails to them in which you wish to accept or block. People who reply to the Box Trapper reply will automatically get listed in the white list and will not have to reply to Box Trapper in the future.