Quick little Office 365 issue I cam across today, first a bit of background. I am migrating a client from Exchange 2003 (yes I know!) to office 365. Rather than any integration or swing migration etc, it is literally a case of creating the tenancy in 365, sync up the users and import the psts via azure storage.
First AD connect was setup and sync to 365, no problems – until I went into Exchange online and notices that zero mailboxes had been created and I also could not create via powershell. I re-synced and had the exact same issue.
Why Where no Mailboxes Created in 365?
The reason is quite simple when you think about it, the users already had a mailbox in Exchange 2003, this means the msExchMailboxGuid was populates meaning the Azure AD connect thought a 365 mailbox did not need creating.
The msExchMailboxGuid needs filtering from AAD so that on a re-sync the mailboxes are created.
The Fix
How I resolved this was first move remove the OU from AAD that was being synced to 365, on the next sync 365 thinks the users have been deleted and will remove them from 365. We then need to setup AAD to ignore the msExchMailboxGuid.
- Run the Syncronisation Service Manager
- Select Tools > Connectors
- Then select your connector and right click and properties.
- Locate the “select attributes” option and untick msExchMailboxGuid (See image below)
Then add the user OU back into AAD connect and re-sync, you will find uses now have mailboxes created.
