Assigning Multi-factor Authentication for Office 365 accounts gives more security to Exchange Online, allowing users to have more than one verification method in the sign-in process. It checks if it is signed by the authorized user of Office 365. You can also say that MFA is a two-step verification process to Office 365 account. For this, we have to enable MFA for each user account. Once it is enabled, the user must accept a text message or the mobile app for verification. After it is been verified, you can use your Office 365 mailbox.