All the diagnosis information and messages are presented through the Google Webmaster Tools UI, not through email. There is an option in Webmaster Tools to forward messages to email, but this is opt-in.
You have a point though...there are lots of "from google" false emails floating around. As you know it's a tough problem to solve
This is a great service. Google should set up an opt-in email notification as well.
It helps the webmasters build better sites and teaches them to check the Google website tools that allow them to groom their site for best indexing on Google. That's great.
Webmaster Tools has opt-in email notification. Here are details: http://googlewebmastercentral.blogspot.com/2009/06/to-make-webmaster-tools-message-center.html
The "Malware details" feature (mentioned in the article), however, doesn't send you any notifications just yet.