Hi @APTOS
Once a moderator approved a quarantined email, a message with the subject in a form like "Approve: <quarantined message subject>" would be sent to the system.
Thus you may either search via message trace for the message subject in Exchange Admin Center, or use the following command to search via EXO powershell:
Get-MessageTrace | Where{$_.Subject -like "Approve*"} | fl
The Sender Address part would show the moderator who sent the approval email.
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