The sandbox that we provisioned to you (our Partner) is the full Marketing Cloud environment. And by the way, even though we are calling it "sandbox", it is not a cloned environment. It is an account on the actual Marketing Cloud system.

Because a "sandbox" environment is strictly for NFR use (Not For Resale), the terms of the "sandbox" EULA stipulates that the environment cannot be used for production purposes, i.e., it cannot be used as a tool for development toward a web property that goes live/production. So, with these environments, you have the full function of the Marketing Cloud.

However, we ask that you do not use it with any kind of live/customer/production data. (If you do, you would be in violation of the EULA.) And, please do not use it for any kind of load/stress testing also.