Having to wait for days before taking action could often mean that we would have to work months cleaning up the mess. The normal university procedures CAN'T be completed in less than a week. Even if they could, the university administrators don't understand the issues and we spend days getting the ideas across. In cases such as chain letters, for example, we might have to act immediately to prevent the system from becoming totally unusable. Even electronic mail to other sites is not tamper-proof.
Any good postmaster can forge mail from anybody to anybody.
With care the forgery is totally undetectable. If you always believe the administrator, you will effectively concede to him or her the ability to take advantage of anybody at any time for any reason. But if you always believe the student, you will effectively give the student the ability to get away with anything he or she wishes to do, including violation of serious laws.