Monitoring tools

Hi, I would like to know how do you guys monitor your web and email Virtualmin servers. Lets say you have several servers with bunch of domains, emails, and websites. I wonder what Virtualmin options or additional tools you use to find out:

1. Is some website is not malicious and not sending spam emails or generate big load

2. How do you prevent that your users not sending spam emails from their malicious computers

3. How do you automatically get notified about these events before your server users don't find out it.

Thanks