In support, we hear from people in this “duplicate mailbox” situation relatively often. When this happens, our customers ask us for the best way to recover. In my experience, there are typically two ...
Published Sep 11, 2019
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Shaun Jennings the on-premises original mailbox is soft-deleted (the ExchangeGuid in the error message is that mailbox's). The original user in on-premises is now a RemoteUserMailbox and its ExchangeGuid has been set to match that of the EXO-based mailbox. I'm doing New-MailboxRestoreRequest in EXO v2 PS like this:
New-MailboxRestoreRequest ` - Name <PSmtp> ` - BatchName "Migration via Restore" ` - RemoteCredential $Credential ` - RemoteHostName <on-premises EWS/MRS proxy FQDN> ` - RemoteDatabaseGuid <on-premises MDB Guid> ` - RemoteRestoreType DisconnectedMailbox ` - SourceStoreMailbox <ExchangeGuid of soft-deleted on-premises MBX> ` - TargetMailbox <ExchangeGuid of EXO MBX> [ENTER]
It seems like I'm following the instructions in the "How to recover when a mailbox...." article perfectly, with the exception that for step 7, I'm also including the Name and BatchName parameters. Otherwise I've executed everything exactly as instructed. It's really strange too whereas I can see in the report that the on-premises mailbox is connected to and its items are successfully copied to the cloud mailbox.
Going back to your question about the main AD account - it was never deleted from on-premises AD, nor from Azure AD, it was mailbox-enabled in EXO before EXO was aware that there was already a mailbox for it in on-premises.