I don't think the dummy gateway sends emails, but is just for testing payment processes to ensure plan access and workflows is working appropriately. Typically the email you receive is from PayPals end or whatever gateway you're using regarding a purchase made. Example subject of an email PayPal would send.
Item #XXXXXX - Notification of Payment Received from XXXXXXXXXX
If you'd like CBSubs to send you a customized/personalized email you could CC the emails to your self via plan configuration on the presentation tab or use CBSubs Emails to customize a personalized email.