Notifications are used to get a notification when specific number of triggers are reached on domain. You will get notified by email about domain that was triggered. The reason is to track specific domain query triggers on your network interface or on your router. DNS Sniffer makes sure that all your domain are tracked on your network interface.
Image represents free example for Notification list, where you can add, remove the domain or subdomains from the list. This also gives you ability to set up number of hits, on which is your domain triggered. Count hits will increase the number and as soon it reaches the "Notification Hit" it will email you about this domain. By adding domain you will have to add a network interface weather you public IP or Local IP depends on where this Solution being installed. You can reset the notification counter if you want to get email again about your notifications domain.