Hi @Innocent Heartvoice ,
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As far as my research, there is no direct way to achieve this in Exchange Server 2019, but you can use the following command to create a transport rule that triggers when mailbox usage exceeds 80%:
New-TransportRule -Name "Mailbox Usage Alert 80%" -SentToScope NotInOrganization -SubjectOrBodyContainsWords "Your mailbox is nearing its capacity" -SetAuditSeverity High -NotifySender "SenderNotify" -NotifyMessage "Your mailbox is nearing its capacity. Please consider archiving emails."
By default, transport rules are evaluated during message submission. To schedule the rule to run periodically (e.g., every hour), you can create a scheduled task that runs a PowerShell script invoking the transport rule.
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