From your last paragraph the term you are looking for is "common carrier".
Email goes over common carrier networks between private hosts and so is pretty close to a common carrier network. Twitter isn't and doesn't. Maybe there should be a way for web services to provide a similar service with similar protections.
Email goes over common carrier networks between private hosts and so is pretty close to a common carrier network. Twitter isn't and doesn't. Maybe there should be a way for web services to provide a similar service with similar protections.