Actually, it is not the marking of a document that makes it classified, it is the content. People with security clearances are trained to recognize what is classified. If someone copies a top secret document, removes the cover sheet and markings on it and emails it to someone with a clearance it is still a top secret document. They must report it as a security violation.
If that's the case, how the hell is Blumenthal getting this "classified" report to begin with? It all stinks to high heaven. Only a Clinton would a) think up of a shadow SoS cabinet so to speak; and b) use some sort of shady e-mail server to exchange ideas outside the view of public inspection.