Teams Login explanations (UPN vs. E-Mail vs. SIP address)
I’ll explain how Microsoft Teams handles SIP addresses, logins, and identities in a hybrid Exchange environment where the user's Primary SMTP and UPN differ. I'll detail how Teams handles login with UPN, what role the Primary SMTP plays, how SIP addresses are resolved and used (including how this has changed over time), and what happens if the SIP entry is missing from proxy addresses in hybrid identity scenarios. Teams Sign-in Identity (UPN vs Email) Teams uses Azure AD for authentication, so users sign in with their Azure AD User Principal Name (UPN) (even if the UI says “enter email”). In practice you enter the UPN (or sometimes just the username portion) and password. For example, if your UPN is user@contoso.com , you log in as user@contoso.com (or just user on domain-less clients). The primary SMTP address (your email) is not used for login by default. (If UPN ≠ SMTP, the user still must use the UPN unless you set up Azure AD’s ...