You could also check the following.
https://learn.microsoft.com/de-de/security-updates/windowsupdateservices/18127666
If your e-mail notification is not working properly, one place to look is the SoftwareDistribution.log file (found in your WSUS directory, usually …\Program Files\Update Services\LogFiles). One error message that is symptomatic of an incorrect SMTP configuration is the following:
EmailNotificationAgent.WakeUpWorkerThreadProc Exception occurred when sending email of type Summary: System.Net.Mail.SmtpException: Failure sending mail. ---> System.IO.IOException: Unable to read data from the transport connection: net_io_connectionclosed.