I would put a simple “grep <whafever> mail.log || curl ntfy.sh” or something like that. Ntfy can send you alert on the phone if some check failed or passed. For pass just use && :) Simple and it works.

Yeah better fit but a bit of trouble to setup… What’s your opinion on Icinga? Never used it myself.

Give https://github.com/louislam/uptime-kuma a try. I’m planning to do the same for similar use case. Sensu (sensu.io) is a more sophisticated option but it requires more infrastructure and there is a bit of a learning curve with it.