There might be a scenario where the environment has Azure AD synced users from local Active Directory. The mailboxes will be created directly in exchange online with no hybrid configured from the underlying time as a rule for new businesses.
Usually developers for customizing the login experience for different business units in their application consume the local extension AD attributes and its usually fine for fully on premise environments.
If we have exchange installed in the environment , the active directory schema will be extended to include user extensionattributes in the exchange mailbox properties.
There is another option of Using the Exchange Server install media, extend only the local Active Directory schema. Usually this option is not recommended. Doing this would add Exchange attributes to the local Active Directory. These attributes could then be set, and Azure AD Sync would then be configured to sync these attributes to Office 365.This option requires much testing, and there is always risk associated with AD schema changes.
Even in hybrid setup these values gets populated in Exchange online via exchange hybrid configuration for all users.
In the third scenario where we do not own a exchange hybrid and if the developer is using Azure AD via graph API and expecting these values on azure AD for the customization. In this case we have a better option of extending these values from the Azure AD connect by running them again and selecting only the required AD extension attributes.Continue reading