Find Out How Much Storage Space Your Mail Is Occupying on the Server
1. On the upper menu bar, click Tools.
2. Click Mailbox Cleanup. A dialog box appears.
3. Click View Mailbox Size. In the dialog box, you can now view the details of locally used storage.
4. On the Server Data tab you can see how much space is left on the server. The amount of space shown will be cumulative if folders contain subfolders.