Yes. Here’s how you do it:

• Click Options in the upper-right corner of your Mail page.
• Click Spam from the list on the left.
• In the “SpamGuard” section, after the line “Empty Spam folder”, you can specify how often you’d like us to empty your Spam folder by selecting from the pull-down menu. We do it automatically once a month, but you can select two weeks, one week…or immediately!
• Above your spam options, click Save Changes.