Exchange Server 5.5

When I look in Exchange Administrator to clean out mailboxes with lots of data my largest culprit is the “Internet Mail Service” account. It says that it’s mailbox is the exchange service account. I’ve logged in from an Outlook client and configured myslef to be that service, but it shows up empty? I’ve logged in as Administrator and had that mail box open as an additional mailbox but still there’s nothing there to delete. Do I even want to clean this out? What is up with this and how can I clean this out?