Exchange 2010 Migration

Jason Harding 1 Reputation point
2021-08-31T14:37:00.947+00:00

Hi there,

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.

Kind Regards,
Jason

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  1. Limitless Technology 39,331 Reputation points
    2021-08-31T17:12:29.673+00:00

    Hello,

    If the mailbox still exists in on prem exchange then you can map to the user then export it to .pst or access via Outlook or OWA.

    Alternatively, please inform to that MS Engineer to involve L2 or L3 team to help you quickly at earliest.

    If the reply was helpful, please don’t forget to upvote or accept as answer.

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  2. KyleXu-MSFT 26,206 Reputation points
    2021-09-01T08:11:57.297+00:00

    @Jason Harding

    Does mailbox is migrated in the way of hybrid? Do you mean this mailbox is on Exchange online now? Do you want to migrate it to Exchange on-premises?

    If so, you could try to create a AD account on Exchange on-premises, then enable remote mailbox for this AD account. After that, check whether this AD account is connect with Exchange online mailbox.

    If this AD account is connected with Exchange online mailbox, you will could migrate mailbox from Exchange online to Exchange on-premises with remote migration.

    If this AD account cannot connect with Exchange online mailbox, I would suggest you export PST for this mailbox, then delete mailbox and AD account for this user, then recreate a new mailbox for this user directly.

    If the response is helpful, please click "Accept Answer" and upvote it.
    Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

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  3. Amit Singh 4,846 Reputation points
    2021-09-30T06:47:19.157+00:00

    You should try Exchange Deployment Assistant, available from Microsoft and provides step-wise instructions by checking all the required prerequisites. You can also check out How to Migrate Exchange to Office 365 for help.

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