Let's assume Gerry has a laptop and she lends it to Sarah. Sarah logs into her email account on Gerry's network, does some work and hands it back without logging out of her email. Does since Gerry owns the laptop and pays for the network, does Gerry have the right to read Sarah's email?
If not, why does this differ from the rights of companies to read private emails?
Note: I realize that most companies merely read the traffic that includes personal emails or any personal saved email files.