Having an Identity Crisis
My email address is my identity
In Active Directory on-premises or Azure Active Directory (AAD), used by Office 365, our User Principal Name (UPN) is often the same as our email address. These days, we often log in with our email addresses, which means that whatever we’re “using under the hood” from an authentication point of view is the same as our email address. This convention of making our email address the same as our UPN is common practice and even advocated by Microsoft.