There are 5 kind of notifications you can enable/disable.
Rig offline : Notifies you when your rigs goes offline.
Temp overheat : Notifies you when the temperature of any of your rigs exceed the limit temperature.
Watchdog reboot : Notifies you when your rigs are rebooted by watchdog.
Hashrate Lost : Notifies you when your rigs hashrate drops. It is also related with the hashrate lost volatility.
Working GPU down : Notifies you when any of your working GPU is down.
You can also set GPU overheat temperature, notification repeat frequency, watchdog alert frequency and hashrate lost volatility.