Be sure to take advantage of the spam tools in your control panel, specifically SpamAssassin. This can filter out up to 80% of your spam!
Do NOT use a "catch all" mailbox. This is when you have email sent to your domain but not to an email address already set up forward to an exiting email address. This will increase your spam and open you up to a dictionary spam attack. Catch all boxes are disabled by default, but can be modified in your control panel.