I don't really understand the interface check. If the network interface is down... send an email about that? Through which network link? That's one of the reas

I don't really understand the interface check. If the network interface is down... send an email about that? Through which network link? That's one of the reasons you really want a centralized monitoring system; an offline (link down, system down) system cannot inform you that it's offline, a monitoring system can tell you that.