Compress an Outlook (not Express) database?

At my company we use Outlook (not Express) as out email client. I believe Outlook links into a server provided by our ISP. Even though I delete emails from the Outlook client, I still get messages that my email database is full. At another job we used Lotus Notes where I had to initiate a database compress to really remove the emails. Is there a similar process in Outlook? If so where do I find this command?