From Outlook 2013:
All users with an SPU email address use Office 365 and (as of fall 2014) have a storage limit of 1 Terabyte.
Current Faculty and Staff email MUST be maintained in SPU's email system. Faculty and Staff are asked to NOT create local archives of email messages that are stored on university assigned computers, a personally owned computer, or removable media.
Documents, pictures, and other files that are attached to email messages will count toward the total email storage limit. If you are nearing the storage limit, please see Storage and Backup of Email Items for methods of saving attachments so they do not count against your email storage space.
All items stored in an email account are included in the data storage amount, including items in the Deleted Items folder. Be sure to empty the Deleted Items folder if space is running low.