Normally, you would use Control Panel / Server / Alerts but you can edit:
Edit or Add Value of AlertNames as a type REG_MULTI_SZ
Each UserName and/or ComputerName is entered on a separate line.
You can alter how often the Server service checks for alert conditions by editing:
and changing AlertSched which is a type REG_DWORD. The default is 5 minutes and the allowable range is 1–65,535 minutes.