(Don't ask me why the fact that you have no email privacy as a Harvard employee is kept secure behind a login wall.)
While I am not an attorney, I believe the reason the University policy is only accessible through logon is that this provides the administration with a record of folks who have accessed the policy, thereby potentially limiting the ability of people to claim they were not aware of the policy.
Added 10pm 3/11: I have now heard from two very experienced lawyers who giggled at this theory but don't believe a word of it. Any competent lawyer, one of them said, would advise that the policy needs to be as visible as possible to reduce the risk that someone will claim not to have known it. So thanks to my informant, but the theory is too cute by half.