If you are receiving errors about being close to your quota for your Exchange e-mail account, follow the instructions given to attempt to decrease the amount of e-mail saved to your online account in an attempt to avoid reaching your quota.
Open Entourage. Right-click on your Exchange mailbox in the Mail Folders list. Then, click the Folder Properties from the drop-down menu.
The Folder Properties window will pop-up. Click the Storage tab.
From this window, you can view the size of each folder on the server. Click OK when done.