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This is because of the changed port. If you have configured the SMTP under port 8009 and changed it afterward that causes the issue.
1. Could you please stop the scheduling service.
2. Navigate to C:\ProgramData\Telerik\Configs
3. Open Telerik.TestStudio.Scheduling.Client.exe.config and double check whether the port is 8010. If not please change it.
4. Do the same for Telerik.TestStudio.ExecutionManager.exe.config file
5. Save the file and start the scheduling again.
Let me know if that helps.