Hi @Labellep ,
From the error you shared, it seems that the issue is related to the arbitration Mailbox "MSExchApproval 1f05a927-3be2-4fb9-aa03-b59fe3b56f4c". Please try recreating this system mailbox and rerun the setup to check the result:
1.Open ADUC, remove the SystemMailbox{1f05a927-2390-47c4-81b3-55dc22299269} in CN=Users:
2.Run the following command from a Windows Command Prompt window:
<Virtual DVD drive letter>:\Setup.exe /IAcceptExchangeServerLicenseTerms /PrepareAD
3.Run the following command in the Exchange Management Shell:
Get-User -ResultSize Unlimited | where {$_.Name -like "SystemMailbox{1f05a927*"} | Enable-Mailbox -Arbitration
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.