When working with an Active Directory connector in the Quick Connect or Active Roles Synchronization Service Console, the extensionAttributes are not present on any objects.
These attributes are also missing in Active Directory Users and Computers when connected to a target Domain Controller in that Active Directory Domain.
Use a different attribute to store the desired value.
Extend the Active Directory schema in preparation for installing Microsoft Exchange:
For assistance with this option or is any issues are encountered, please contact Microsoft Support.