Action: Directory sync: Review your UPNs and other Active Directory attributes Your Active Directory environment must be ...

Action: Directory sync: Review your UPNs and other Active Directory attributes  Your Active Directory environment must be properly configured for directory synchronization with Office 365. In particular, the userPrincipalName (UPN) attribute, also known as a user logon name, must be set up for each user in a specific way. When synchronizing user accounts from your on-premises Active Directory to Azure Active Directory, the UPN must include a publicly routable domain after the @ character. If the UPN has a suffix that's not routable (for example, [email protected] or [email protected]), the IdFix DirSync Error Remediation Tool will catch this issue with a "topleveldomain" error. Learn more at Clean Up Active Directory.