Two-factor authentication is a technology that provides identification of users with the combination of two different components. These components may be something that you know (like a password, UserID, etc) and something that you posses (a good example can be a smartphone, or USB-key, etc.).
The use of two-factor authentication to prove you identity is based on the premise that an unauthorized actor is unlikely to be able to supply both factors required for access. If, in an authentication attempt, at least one of the components is missing or incorrect, your identity is not established with sufficient certainty and access to the Mailbox that is being protected by two-factor authentication remains blocked.
We strongly recommend enabling two-factor authentication on your account to maintain a high level of security and protect your sensitive information from getting in the wrong hands.