In rare cases you’ll see this error message on the first run of Easy365Manager:
This problem is an indication that one or more Exchange related attributes were not found in your on-premises domain.
When you install Exchange on-premises the Active Directory schema is extended with multiple Exchange specific attributes. Some of these attributes are a vital part of mailbox management on linked accounts (Office 365 accounts that are synchronized from your local AD).
If you want to use Easy365Manager to manage Office 365 mailboxes and licenses as an integral part of your AD user management your local AD must be updated with the Exchange schema extension.
To confirm if the Exchange schema extension is missing from your domain, run the script in this article. If the Exchange schema version is 0 you must update your schema with the Exchange schema extension.
How to Fix This Error
To update the Active Directory schema with the Exchange schema extension, download Exchange and run the schema extension.
Download Exchange 2016 CU12 here.
Mount the iso file and run the following command from the mounted drive:
Setup.exe /PrepareSchema /IAcceptExchangeServerLicenseTerms
Refer to the official documentation from Microsoft for more information on extending the Active Directory schema with the Exchange schema extension.
After extending your AD schema you must reload the schema in Azure AD Connect.
Open up Azure AD connect, click Configure and select Refresh directory schema: