By default the reachability notifications are off. Go to your profile settings to turn them on.

They're all claimed, but I didn't get any "host is offline" e-mail. But you gave an idea: I could create this alert, couldn't I?

Hi! I think this can be done if you connect (claim) the nodes to the cloud. Cloud should send a reach-ability email if a node goes offline.

To see older data from them when they are offline, set up streaming/replication and connect the parent to the cloud too.

I would like to know when a node went offline, and if it is possible to check it's metrics when it's still offline.

Know when a node went offline?