User Principal Name

A User Principal Name (UPN) is the Entra ID identifier for a user, in the format user@domain.com — typically the user's primary email address but technically distinct from the email address. The UPN is what users type into the Microsoft 365 sign-in page. In hybrid identity, the UPN comes from on-premises Active Directory; mismatches between the UPN and the user's primary SMTP address cause confusion and should be resolved (Microsoft recommends aligning UPN with primary email). The UPN is also called the sign-in name in the Entra admin center. Don't confuse with SAM-Account-Name (the legacy on-prem identifier like DOMAIN\username).