This article really says it all about virus alerts coming from email gateways.
After blocking a flood of Mydoom e-mails, it spams users with alerts that create a general panic.
That’s true even in small offices. You’ve got other email gateways sending back virus warnings in response to emails with spoofed “from” addresses as well as virus warnings coming from our own gateway about incoming infections. Despite numerous explanations and warnings about what these are, the first instinct of an end user is to call the IT Department. When you are the guy getting those calls and emails, you get swamped very quickly.