If the email is based on the Exchange/AD paradigm then o365 is undoubtedly far more secure. An expertly administered postfix system might deliver mail more secu

If the email is based on the Exchange/AD paradigm then o365 is undoubtedly far more secure. An expertly administered postfix system might deliver mail more securely but probably has a weak web frontend. I too prefer offline Office install for my own use, but they are systemically less secure. Just rampant exploitation.