Find "Online Photo" in Inside ND and click the icon to open the site.
Open the desired course and click the email icon to send a message to a Google Group.
Instead of a Google Group, you can use Sakai's Email Archive tool.
If you're already using Sakai for the class, this may be more convenient.
In either case you'll get a single email address for sending a message to the entire class.
These lists are created and updated automatically with information provided by the Registrar.