I am getting this error while testing the email.pinotifications
Could you please check notification configuration (PI AF --> Configuration--> PIANO) . Check SMTP authentication. You can try anonymous for sake of testing but always recommend windows.
The error seems to imply that the user running PI System Explorer does not have access to the machine where the PI Notifications Service is running.
Can you try the test send using PSE from the same machine where the PI Notification Service is running to confirm that is indeed the issue ?
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