Updating Microsoft 365 User Accounts to use a New Domain

A reader asked how to update user email addresses and UPNs. As it turns out, this is not a very difficult technical challenge. The problem lies in the aftermath. It’s easy to update the primary SMTP address for a mail-enabled object or assign a new user principal name to an Azure AD account. Then problems might come into view, like needing to adjust the Microsoft Authenticator app to make MFA challenges work for the new UPN.