Problem: An error message indicating the failure to synchronize internal domains in scheduled user data synchronization for Gmail.
The possible reason is as follows:
This occurs if your organization started to use the Gmail protection functionality in public preview. During that stage, Cloud App Security was not granted the domain read-only permission during access grant, and thus not able to synchronize the internal domains of your organization.
Perform either of the following:
  • Remove the Gmail service account that you used in public preview, and grant Cloud App Security access to Gmail again.
  • Go to Advanced Threat ProtectionInternal Domains or AdministrationGlobal SettingsInternal Domains to manually add the internal domains of your organization. Repeat this every time there is a new domain created for your organization.