When you configure the forest settings in Managed Domains table in the Active Directory extension you should specify the scenario for the Exchange management that you are plan to use in your environment. These values are possible:
- Enabled for all recipients, with Exchange Extension.
- Enabled for remote recipients only, with direct attributes update in AD.
- Disabled - you will have no mailbox management actions available for Active Directory objects.
For more details about Exchange Management please see this article: Exchange Management Overview – Cayosoft Help Center.