Have a look at our application called: Resource Notifications >> http://www.clarizen.com/appsmarketplace/item/Resource-Notifications.html.
This app sends a notification to a resource upon assignment to an active or draft task.
Please note all apps are customizable. You will have the ability to tweak them according to your needs.
If you would like to further assistance modifying the rule, please hop on our free Advanced Q&A ( http://www.clarizen.com/live-demo.html#second). These are great resources for consulting with our experts and visual answers to your questions.