Q. Is there a way when I add an activity for a project for users to automatically be emailed without them being assigned to every activity entered?
A. Yes, the "Notifications" button found on each project details page takes you to the notification rules area. In a rule details you can enable the "Also include" option and then choose users to be included to the rule from the global user list.
You can have more than one rule per project to accomplish this, or you can simply add extra users to an existing rule.
For complete info, please check Online help corresponding article: