All the documentation I can find speaks to notifications to a specific customer or organization (multiple email addresses with the same one customer) and where a service ticket/problem has been reported by them.
We have a softwre product and I am looking for a feature within Service Desk where I can send an email to all customers for cases where we want to make them aware of a service issue like a software bug or where we would like them to all be informed of an upgrade patch or other remedy.