Having the 'owner' of the e-mail address have the only access is a better extreme than having everyone have access, but I don't think that's feasible. People wi

Having the 'owner' of the e-mail address have the only access is a better extreme than having everyone have access, but I don't think that's feasible. People within Microsoft will always have the ability to access e-mail accounts, the question is if they are the right people and how big that group of people should ever be. If you are talking about secure e-mail cryptography philosophy along the lines of PGP, ProtonMail, et cetera, sure you can achieve that through those means. Otherwise it's a pipe dream with a product like Outlook that's built for businesses and having AD style control.