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First I should describe our situation a little bit. We have 2 different domains. Let's call them contoso.com and contoso2.com. Previously we only had contoso.com but there was internal conflict and the company decided to split up and create their own domains and the whole migration journey started.
So we first linked our mailboxes from contoso.com -> contoso2.com and then migrated the mailboxes to Exchange Online. So the mailboxes were all still at contoso.com when they got moved to Exchange Online.
Though 2 of our shared mailboxes are causing us some serious trouble right now. Our en-prem Exchange 2016 cluster says that those mailboxes were successfully migrated to Exchange Online, but they are definitely not there when I check the mailboxes. Neither on exchange admin center nor when I connect to Exchange Online via Powershell.
So I check en-prem Exchange server too with get-mailbox, but no luck either. Even if just list all mailboxes en-prem and later on Online, I cannot find them. I thought they might gotten renamed into something obscure or whatever. 5 days ago my colleague swears he saw both mailboxes successfully being migrated via "Get-MoveRequest -status Completed", but they are definitely not appearing on the same list anymore. They are gone.
Luckily both shared mailboxes aren't really important and could just be recreated without much of a loss. But I'd still like to understand how this could have happened and how to fix it, as it would safe us quite some time to gather all the information again of one of the mailboxes that contained warranties of all our laptops. This time it was 2 not very important mailboxes, but next time it could be something crucial. We are done with about 25% of all mailboxes, so I'm still afraid it might happen again with something more important.
If there is anything else I can add, I will be happy to share.
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Hi，@TomCruise-7376
I'm glad you got closure on your question. It turns out that changing the mailbox type before migrating the mailbox caused the shared mailbox to go missing.
If my answer is helpful to you, please mark it as the answer so that other users can refer to it. Thank you for your support and understanding.
Hi，@Tom Cruise
Thanks for posting your question in the Microsoft Q&A forum.
According to your description, although the migration was successful, the customer did not find those two shared mailboxes.
First of all, let's confirm with you:
Here are my suggestions:
Try Get-aduser username -Properties Mail,TargetAddress | Select name,mail,targetaddress. A user whose mailbox has been migrated to EXO in hybrid mode should look like targetAddress: username@contoso.mail.onmicrosoft.com and an on-prem user should have a blank one. In on-prem, see if Get-Remotemailbox shared@contoso.com finds it. Check the user in EntraAD and the 365 admin center.
If my answer is helpful to you, please mark it as the answer so that other users can refer to it. Thank you for your support and understanding.
If you are not able to find the mailboxes, you can check it through various ways-
1. Check the migration logs on your on-premises server.
Use PowerShell command: Get-MoveRequestStatistics -Identity <MailboxName> | fl
2. Do check hidden or disconnected mailboxes
3. Also check if they were accidentally deleted.
For prevention, backup the important mailboxes to avoid sudden data loss. If you want any more specific commands or if any of the steps are unclear, let me know!
Thanks for your answer and you tooBruce Jing-MSFT,Amit Singh . It looks like my colleague migrated the mailbox before converting it to a shared mailbox. Since the sync to EXO happens from contoso2.com, and he had changed the mailbox-type during the final migration moments. But he had to change it in contoso.com domain. Contoso.com domain didn't sync it in time to contoso2.com domain, which led to EXO to believe that the mailbox is a mailbox-user instead of shared mailbox. I had to assign an E3 license to the mailboxes at EntraID, then they appeared. Converted them, took license away again.Job done.