This tutorial teaches you how to view the storage capacity of your Exchange account in Outlook 2013.
Your quota on the Exchange system is taken up by email, calendaring and any other information that you store in Exchange. Queen’s offers 5 GB of space for every user on Exchange. Additional storage space is available for a fee.
It is important to be aware of your quota status because you will be unable to send mail if you exceed your 5 GB limit. To clean up your data and free up space, remember to periodically delete the items you no longer need, and empty the Deleted Items folder.