I do experience this kind of ruling in two companies in my career in my country which both are multinational companies (electronics and semiconductor),before you were given a contract to be signed, the HR relations manager will be givng you a sort of handbook sort of manual, written all your rights and their rights, if you agree and off course no questions asks (if have, they will explain) / then it's time to sign this contract.

Company email accounts are company property, even in cases you do not agree, w/ or without the notice given to you, they can access your mails,some are just being polite to asks and informed you first and that is good because it means the company respect your rights.