Hi, @Lexi Ours
Based on your description, I understand that you encountered an error and need to create a user multiple times, and you can not find the mailbox of a specific user.
Error message "Exchange Online: An unknown error has occurred. Refer to correlation ID" usually occurs due to a configuration setting failure for the user's mailbox.
So, we should find the real cause of the error firstly. You can get the actual error message from PowerShell, either via the Exchange cmdlets or via MSOL:
Get-MsolUser -HasErrorsOnly | fl DisplayName,UserPrincipalName,@{Name="Error";Expression={($_.errors[0].ErrorDetail.objecterrors.errorrecord.ErrorDescription)}}.
More information can be found Troubleshooting Exchange Online Mailbox Provisioning Errors - Faris Malaeb (powershellcenter.com)
In addition, could you provide more information so that I can proceed to the next step of troubleshooting?
1.What is your work environment?
2.Did you encounter an error when creating or deleting a user, or was it anything else?
3.What is the status of the affected users now? Has it been created successfully? Will he be able to log in to his email?
4.Did you do anything else before you encountered the error?
You can still provide additional information that is not included in the above questions.
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