Just a regular everyday normal muthafucka.
I use ssmtp as well for a simple sendmail replacement. It takes over the sendmail command, doesn’t open any ports. You configure it for the domain you want and tell it what server to send everything to and it works.
True, but SQLite is not recommended in production settings, and is quite often the source of Nextcloud slowdowns, in my experience. A dedicated DB is the first thing I recommend for a production Nextcloud instance.
Oh and to be clear, in this instance, “production” means “people depend on this”, be that your family group, team/department, fraternal order, church group, etc. as opposed to “I’m just playing with this thing.”
If you’re willing to go that route, check out Zabbix and Icinga2 as well. They’re compatible with Nagios checks but the user interface is better.