Thanks Habitual for your answer. Yes, I know zabbix, though didn't test it yet. I wanted to use collectd as it states to be less demanding on system resources.
Maybe I was not clear enough in my first post, but I didn't ask about how and what (which software) to use for sending notifications by e-mail, it's more or less clear, it is doable with collectd too. I wanted to know if there is some Best Practices for specifying conditions when this notifications should be send. I understand that this should decide admin for his particular server, but so far I'm not sure what to do with Zombie Processes. As I said already, there are Zombie Processes reported in "Processes Graph" (screenshot in my first post), and I wanted to know if it's normal in general that once in a while Zombies are appearing? I think ideally they shouldn't be there, even if they are appearing just for a few seconds.
During this time I already found which software is making Zombies, it is webmin. Here is lines from ps utility with Zombie Process:
1 S 0 4070 1 0 80 0 - 16497 poll_s ? 00:00:00 miniserv.pl
1 Z 0 10276 4070 1 80 0 - 0 exit ? 00:00:00 /usr/libexec/we <defunct>
and it disappears very quickly, the same repeats after a short while, and that happens all the time while webmin is running. I will write about this in webmin forum of course, but so far question is about Zombies itself, on what conditions would be better to make e-mail notifications? Before I found out that something (webmin) is making Zombies all the time, I was sure to make notifications on any Zombie Process right after it's being detected, but now I'm a bit confused...
Thanks in advance!