A previous employee started migrating users from on-prem Exchange 2010 to Office365
He left and didnt provide any information so this was given to me.
A user was listed in Office365 but stated that their Mailbox was still hosted on-prem.
Having looked around and researched, many suggested this happens due to the MSExchMailboxGUID has a value which tells Office365 that its hosted on-prem and not to provision a Cloud mailbox.
The solution to this was to make this value NULL and resync which I did.
Unfortunately, this did not pull the emails from the on-prem mailbox and I am working with a MS Engineer in trying to recover this.
I took note of the GUID in the users AD Attributes.
So is there a way to get the users on-prem mailbox again? Like either reconnecting it to the AD user (if this can be done, I will Export the Cloud mailbox to PST, make the change, then simply export the on-prem mailbox, remove the GUID value, and then import the PST to users Office365 account.
Or is there another way? Like attaching the GUID to a new AD Test user to access it? Tried initiating an Export with Powershell but didnt work due to corruptions. Also when opening the Exchange object, it states its corrupted and either click OK to insert Default values or Cancel to read only. The MS Engineer wasnt able to tell me what would happen if I clicked OK as I dont want Mailbox to get deleted etc.
Can anyone provide insight or a way forward whilst I wait for more MS feedback.