This article illustrates how to view your total mailbox size and free/available space within your mailbox account using Outlook 2011 for Macintosh.
1. Open Outlook 2011
2. Highlight your Inbox and right click.
3. Navigate to Folder Properties.
4. Within the Folder Property's window, select Storage.
5. You will see your current mailbox quota under Total Size.
IMPORTANT: Please note the actual mailbox size is not shown. The total size represents the point when size-limit warnings are issued.