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I recently replaced a SBS 2011 PDC with a Server 2019 PDC. The migration went smoothly. A few years before that I switched over to Office 365. Instead of just leaving it be, I tried to uninstall Exchange from SBS 2011. The uninstall failed about 3/4's of the way through and I was unable to uninstall or reinstall so I just disabled all the Exchange services and forgot about it.

Because I couldn’t set up a hybrid environment to transfer mailboxes 2 years ago, I backed up the mailboxes in Outlook, switched to Office 365 and then imported them back into Outlook.

The owners hated Office 365 and had me switch back to Exchange on-premises. I installed Exchange Server 2019 Standard on the new Windows Server 2019 server. When I did the migration it, of course, migrated all the Exchange stuff and I was left with an Exchange dumpster fire.

Despite all that I was able to get Exchange 2019 running properly (mostly). When I installed Exchange 2019 and first went into the EAC the mailboxes from the old Exchange installation were already set up.

I didn't want to have to backup and restore each Outlook mailbox so I setup Hybrid Exchange hoping I could offboard the mailboxes set up on Office 365 to my on-premises Exchange server. Everything seems to be set up properly but when I do a “Migrate from Exchange Online” on a mailbox it fails with the following error:

Error: MigrationPermanentException: Cannot find a recipient that has mailbox GUID ‘578c2104-a29b-474d-8891-7c5a02718b97' 
  --> Cannot find a recipient that has mailbox GUID ‘578c2104-a29b-474d-8891-7c5a02718b97'.

When I try to use “Set-MailUser” to change the on premises GUID for jsmith I get this:

[PS] C:\Windows\system32>Set-MailUser -Identity jsmith -ExchangeGUID 578c2104-a29b-474d-8891-7c5a02718b97
The operation couldn't be performed because object 'jsmith' couldn't be found on 'DCSERVER02.domain.local'.
    + CategoryInfo          : NotSpecified: (:) [Set-MailUser], ManagementObjectNotFoundException
    + FullyQualifiedErrorId : [Server=DCSERVER02,RequestId=dd81f753-8286-4b56-a7eb-91a174ec2f50,TimeStamp=4/25/2020 12
   :21:15 PM] [FailureCategory=Cmdlet-ManagementObjectNotFoundException] 42B1821A,Microsoft.Exchange.Management.Recip
  ientTasks.SetMailUser
    + PSComputerName        : dcserver02.domain.local

Deleting and then re-adding the user from AD or Office 365 makes no difference.

Any ideas on how to get the GUID’s from Office 365 and Exchange on-premises in sync?

Any help would be greatly appreciated.

Here’s some of my notes if it helps:

All of the on-premises mailboxes that are present, were set up by SBS 2011 and were inadvertantly migrated over. None of the mail migrated over. I can access all of the email boxes going to https://127.0.0.1/owa

All of the Office 365 mailboxes are accessible and contain 100% of their mail. None of the Office 365 mailboxes are listed as linked. The on-premises Exchange mailboxes are empty.

In ADSI Edit the on-premises mailboxes are found at
Default naming context [MyServer.mydomain.local] -->
DC=mydomain,DC=local -->
  OU=MyBusiness -->
   OU=Users -->
    OU=SBSUsers

and not
Default naming context [MyServer.mydomain.local] -->
DC=mydomain,DC=local -->
  OU=Microsoft Exchange

I did try changing the msExchMailboxGuid in ADSI Edit to match the Office 365 mailbox.

Set-MailUser -Identity johnsmith -ExchangeGUID 578c2104-a29b-474d-8891-7c5a02718b97

results in:

The operation couldn't be performed because object 'johnsmith' couldn't be found on 'DCSERVER02.domain.local'.

Then

Set-RemoteMailbox johnsmith -ExchangeGUID d1c1908e-96af-4c28-86db-e4b9c817b0e4

results in:

The operation couldn't be performed because object 'johnsmith' couldn't be found on 'DCSERVER02.mydomain.local'.

Then

Enable-RemoteMailbox -Identity "johnsmith@mydomain.com" -RemoteRoutingAddress "johnsmith@mydomain.onmicrosoft.com"
Enable-RemoteMailbox johnsmith@mydomain.com -RemoteRoutingAddress johnsmith@mydomain.onmicrosoft.com -PrimarySmtpAddress johnsmith@mydomain.com
Enable-RemoteMailbox -Identity johnsmith -RemoteRoutingAddress "johnsmith@mydomain.onmicrosoft.com"

results in:

This task does not support recipients of this type. The specified recipient is of type UserMailbox
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There is no AD accounts in Exchange 2019 which is related to mailboxes in Exchange Online, in this situation, we could use SMTP match or hard match to associate them. You could refer to the following articles:

How to use SMTP matching to match on-premises user accounts to Office 365 user accounts for directory synchronization https://support.microsoft.com/en-us/kb/2641663 Dirsync soft matching vs hard matching http://tctblgs.azurewebsites.net/dirsync-soft-matching-vs-hard-matching/ ImmutableID Hard Match in Azure AD Connect https://gallery.technet.microsoft.com/office/Immutableid-Hard-Match-in-d3518b08

For the legacy Exchange 2010, the supported way is to uninstall from control pane, if the server is down, you could remove it from ADSI, and please re-run HCW after that.

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