I've run into a frustrating issue while migrating back to Office 365 from Google Workspace. We had an on-premises Exchange in 2013, but it was decommissioned when we made the switch. Now, one particular user with a full E5 license and all features enabled hasn't had their mailbox provisioned even after a week of trying to resolve it. I've tried commands like `set-user -identity [email protected] -permanentlyclearmailboxinfo`, cleared their license, waited, and reassigned it, but nothing's worked. When checking the mailbox in the Exchange Admin console, it says the mailbox doesn't exist. Even though `Get-User` shows the user but `Get-Mailbox` returns not found. Microsoft 365 Admin states that their mailbox hasn't migrated to Exchange Online yet. I'm at a loss for solutions and even opened a ticket with Microsoft, but they suggest installing Exchange on the DC, which contradicts what I've read about avoiding that. I really need help figuring this out, especially since I'm new to being an EXO admin.
4 Answers
Ensure that this user has a proper proxy address in the attribute editor, specifically the format should be `SMTP:[email protected]`. Without this, the mailbox provisioning won’t trigger, even with the license assigned. If they need aliases, include those as well, but make sure you're using your correct domain name.
Based on previous experiences, you have a couple of options to fix the Exchange attributes issue. If they aren’t in Active Directory because the schema isn’t there, consider creating a custom sync rule to map an extension attribute from AD to the Exchange attribute. There are resources for that if you check Microsoft's docs. Also, you might be able to extend the schema without a full Exchange install. Another alternative is to temporarily install Exchange to get the management tools running and then shut it down. Lastly, if it's necessary, deleting and restoring the user object can work, but I'd caution against that with active users unless absolutely needed.
I’d prefer to avoid deleting any accounts if I can help it, so I really appreciate the advice on other options! Thanks for the resources, I’ll dig into those.
Have you confirmed that the migration from Google Workspace has fully completed? If there are still issues, look into whether there’s a button to click to finalize the migration. It’s possible the system thinks the user still has an on-premises mailbox due to previous settings.
I’m not sure what button you're referring to. The migration process is failing for this particular user because EXO thinks there's an on-prem mailbox, but we’ve been without Exchange for over a decade.
You might need to disable sync for this user first by updating the `adminDescription` attribute to `User_ExcludedFromSync`. After that, restore the user from the Entra deleted users container, get them properly licensed again, and try clearing any Exchange-related attributes from the on-prem object—just leave `mail` and `proxyAddresses` intact. Finally, you can reinstate sync by clearing the `adminDescription` attribute to see if that helps with the mailbox provisioning.
Trying this now. So far, I’m at step 4, and now the MS365 admin mail tab says 'we are preparing a mailbox for this user.' Instead of saying the mailbox isn’t migrated. Hope I'm not celebrating too early lol.
Sounds like you're on the right track! When in doubt, disabling sync and restoring the user usually helps. After you re-enable it, do a quick check to see if the AD user is properly linked to the Entra user. If there are any issues, check the Service Health for any sync errors.
Yes, I’ve already set the SMTP:[email protected] proxy address, so hopefully that’s not the issue.