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paul waterman
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Exchange Mailbox Does Not Exist For Business Standard User

We upgraded a user's license from Microsoft 365 Business Basic to Microsoft 365 Business Standard. We then got a report of failed delivery attempts when others emailed this user. 

The status code for the failed delivery is 550 5.1.10 "This error occurs because the sender sent a message to an email address hosted by Office 365 but the address is incorrect or doesn't exist at the destination domain."

When I select the user's Mail tab in admin.microsoft.com it says the user doesn't have an Exchange Online license.

But on the Licenses and apps tab we can see the Standard license.

The user does not have a mailbox in the Exchange admin center.

I created a new test user and gave it the Business Basic license. Email works and the test user has the expected mailbox permissions settings under the mail tab as well as existing in the exchange admin center.

I'm continuing researching this but I'm not sure what could be going on here. Any suggestions would be appreciated. 


Microsoft 365Exchange

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8/22/2022 - Mon
David Johnson, CD

We upgraded a user's license from Microsoft 365 Business Basic to Microsoft 365 Business Standard


What you should have done is buy a new business standard license and move the user from Business Basic to Business Standard.
Sounds like the user is in a new tenant
Vasil Michev (MVP)

Did you first unassign the existing license? If so, the mailbox got (temporarily) disconnected and will be available after a while. The correct way to switch licenses would be to do it in a single operation, remove the old and add the new without confirming the changes in between.
Other than that, check the status of the Exchange service for the user, and for any provisioning errors (Get-MsolUser -HasErrorsOnly). A check via Get-Mailbox also wouldn't hurt.

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