Disable Legacy Authenication

What is Legacy Authenication Azure AD supports several of the most widely used authentication and authorization protocols including legacy authentication. Legacy authentication refers to basic authentication, a widely used industry-standard method for collecting user name and password information. Typically, legacy authentication clients can’t enforce any type of second factor authentication. Examples of applications that commonly or only use legacy authentication are: Microsoft Office 2013 or older. Apps using mail protocols like POP, IMAP, and SMTP AUTH.