Office 365 hybrid migration with existing O365 mailboxes

Here is the situation:

- We are doing a project to migrate Exchange 2010 to Office 365 using hybrid migration.
- The company already has several existing Office 365 Business Premium licenses assigned to the users. These users already have an O365 mailbox, which got created as part of the Business Premium license but they aren't using these mailboxes.
- All users will get E1 license for email.
- We have got hybrid migration all setup. Users who never had an O365 mailbox have all managed to complete the sync process under migration batch.
- For users who already have an O365 mailbox, it isn't possible to choose these users under migration.
- We tried to remove Business Premium license for users who currently have one assigned, doing so removes the O365 mailboxes and we were able to start the migrate batch for these users.
- However, upon turning on E1 license for users who used to have Business Premium, their old empty O365 mailboxes came back alive and their migration batches all got corrupted.
- We tried to turn off E1 licenses for these problematic users but the mailboxes are still there (under EAC > recipients > mailboxes).

So the question is, what can we do to sync the mailboxes for these users who already had Business Premium? Removing the license from them doesn't help. Can we totally purge the O365 mailbox for these users?

Any help would be much appreciated.
Thomas NZSystems EngineerAsked:
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Jose Gabriel Ortega CastroCEOCommented:
When you connect to of365 using Msol. To remove the users unlicensed and to safely remove them completely from o365

$credential = New-Object -TypeName System.Management.Automation.PSCredential -argumentList  "", ("Password" | ConvertTo-securestring -AsPlainText -Force)
Connect-MsolService -Credential $Credential
#Move To recycle bin
Get-MsolUser | where{ $_.isLicensed -eq  $false} | foreach{ Remove-MsolUser -UserPrincipalName $_.UserPrincipalName}
#Remove users from the recycle bin
Get-MsolUser -ReturnDeletedUsers | foreach{ Remove-MsolUser -RemoveFromRecycleBin -ObjectId $_.Objectid -Force }

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You probably would need to export their mailbox data to PST and bring them back on-prem using Hybrid, then remove the Business Premium License, assign the E1 and move mailboxes again.
carlos sotoIT AdministratorCommented:
if the users are synced from AD, theres no way of removing them in the cloud.

If the users are synced from AD with AADConnect
Just remove the "Exchange online" part of the license, so then the user will no have any mailbox in the cloud but skype, sharepoint will still be available. Then perform a new migration for a single user, when its done reassign the exchange online license and the mailbox should be there with all the email items
Thomas NZSystems EngineerAuthor Commented:
Thanks everyone for the reply.

We have finally got things going by doing the below:

- disable AD sync with exchange online powershell
- all O365 users will change from synced with AD to in cloud
- in O365 portal, remove all O365 users except the admin currently signed into 365
- use powershell to completely purge all deleted users from recycling bin.
- turn on AD sync again. Use powershell to do a full initial sync.
- all AD users will appear in 365 again with the sync type shown as synced with AD
- start remote move migration batches and they all work fine this time
- assign E1 licenses to all users and the users with Business Premium previously didn't get their empty mailbox back (having an active on premise Exchange and an active O365 mailbox at the same time after re-enabling E1 license was the problem we were having before)
Jose Gabriel Ortega CastroCEOCommented:
Select the best answer's and close the question please
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