CloudLink uses the homeMDB attribute of an Active Directory User to determine if it is an On-Premise Exchange Mailbox. When a mailbox is migrated to O365 this attribute is removed and hence the user falls out of CloudLink's scope.

To synchronize migrated users (O365 users), please use O365 Sync functionality from within the Veritas Alta Archiving Manage portal as CloudLink can sync only On-Premise Exchange users.

For more information on O365 sync refer to the article in the Related articles section.