We recently patched our servers to CU9. The FrontendTransport\OnPremisesSmtpClientSubmissionMonitor now reports it is Unhealthy. In the monitoring logs the following is found:

The client submission probe failed 3 times over 15 minutes.
Server 127.0.0.1 on port 587 did not respond with expected response (OK). The actual response was: 550 5.7.1 Client does not have permissions to send as this sender
.
Probe Exception: 'System.Exception: Server 127.0.0.1 on port 587 did not respond with expected response (OK). The actual response was: 550 5.7.1 Client does not have permissions to send as this sender
.
   at Microsoft.Forefront.Monitoring.ActiveMonitoring.Smtp.Probes.SmtpConnectionProbe.AssertExpectedResponse(SmtpExpectedResponse expectedResponse)
   at Microsoft.Forefront.Monitoring.ActiveMonitoring.Smtp.Probes.SmtpConnectionProbe.TestConnection()
   at Microsoft.Forefront.Monitoring.ActiveMonitoring.Smtp.Probes.SmtpConnectionProbe.DoWork(CancellationToken cancellationToken)
   at Microsoft.Office.Datacenter.WorkerTaskFramework.WorkItem.Execute(CancellationToken joinedToken)
   at Microsoft.Office.Datacenter.WorkerTaskFramework.WorkItem.<>c__DisplayClass2.<StartExecuting>b__0()
   at System.Threading.Tasks.Task.Execute()'
Failure Context: 'Server 127.0.0.1 on port 587 did not respond with expected response (OK). The actual response was: 550 5.7.1 Client does not have permissions to send as this sender
.'
Execution Context: ''
Probe Result Name: 'OnPremisesSmtpClientSubmission'
Probe Result Type: 'Failed'
Monitor Total Value: '3'
Monitor Total Sample Count: '3'
Monitor Total Failed Count: '0'
Monitor Poisoned Count: '0'
Monitor First Alert Observed Time: 

How do we resolve this issue?

Hi,

Please restart the "MExchange Frontend Transport Service" on the affected server and check again.

If it doesn't work, please run the following command to have a try:
Add-GlobalMonitoringOverride -Identity "FrontendTransport\OnPremisesInboundProxy" -PropertyName Enabled -PropertyValue 0 -ApplyVersion "15.0.xxx.xx" -ItemType Monitor

The ApplyVersion here is your current Exchange version.

If the issue persists, please provide more error or warning logs for further analysis.

Regards,