Faculty responses revealed a gap between expectations in academia, where privacy is often seen as integral to academic freedom, and the corporate world, in which employees are often told to assume that workplace e-mails are not private. Some professors wondered aloud whether they had been naïve to think that things would be different at a university, and said they were forced to re-examine assumptions about confidentiality.The article does explain that Harvard searched resident dean accounts, which are arguably work related, and even then only searched subject headings for evidence that a particular email was forwarded. If the @harvard.edu account is a work related account, the content belongs to Harvard.
This is a life lesson for all learned people with university accounts: Unless the email account has explicitly been made for your personal use, it's probably a workplace e-mail.