Who owns the contents of my Office 365 mailbox?
Regardless of who pays for your Office 365 mailbox (your department or yourself), you are the primary individual responsible for the contents of your mailbox. Maintaining the privacy of your account's content is important to the university. Keep in mind that as an employee of the university, your email fulfills a business purpose; therefore, specific emails related to business processes could be requested and retained by your employing department.
If you leave the university, your department may request that your mailbox be archived to preserve business knowledge and processes.