Two Factor Authentication (2FA) is an extra layer of security to make sure a person trying to access an account is who they say they are. A password is ‘something you know, but also something that other persons may know or discover. Without 2FA enabled on your Office 365 mailbox, anyone who has knowledge of your username and password would be able to access and misuse your mailbox.

To gain access to a 2FA enabled resource you need your password and the second piece of evidence to prove your identity, either ‘something you have (such as a secure token or keycard) or ‘something you are’ (such as your fingerprint, iris or your voice). With 2FA enabled on your Office 365 mailbox, knowledge of your username and password alone (be that accidental or deliberate) would not be enough to access your mail.