How can I set msExchMailboxGUID attribute to null?
This can be set within Synchronization Rules Editor.
Synchronization Rules Editor as an administrator.
Click on In from AD – User Exchange to edit the Inbound Rule Type.
Transformations. Find the msExchMailboxGuid attribute.
Change it to the
msExchMailboxGuid - NULL - Checkmark Apply Once - Click on Update.
Enable AADSync or AAD Connect and perform a full synchronization.
users may be assigned an Exchange Online license, and MigrationWiz may be used to migrate their
mailboxes to Office 365.