Built in alerts - how does it send email alerts when not added as trigger action?

There is a built in alert called "Alert me when a node goes down".  The only trigger action defined out of the box is:

NetPerfMon Event Log: Node ${NodeName} is ${Status}

But it also sends an email alert.  How is it sending the email/where is it configured to take this action?  I do want to receive the email, but just trying to learn how the product operates.  For custom alerts that I'm creating myself, I've been adding send email as the trigger action.