At the bottom of your Outlook application, on the status bar, right-click Connected to Microsoft Exchange. In the pop-up menu that appears, click Quota Information.
1) Right-click on Connected to Microsoft Exchange at the bottom of your Outlook application on the status bar.
2) Make sure there is a check mark next to "Quota Information." If not, click Quota Information to enable this feature.
Your quota information will be displayed on the status bar in the bottom left-hand corner of your Outlook window. Hover your pointer over the free space indicator to see additional information.