The invention proposes a system and a method for transmitting a message that allows a sender (designated by an identifier) to send a digital content to one or more recipients (designated by one or more identifiers), the content being associated with at least one material subject (each designated by a single authenticator). Thus, to send a message, the sender implements at least one single authenticator of the material subject, discriminant and intrinsic characteristic of each material subject, which serves to anchor the content to transmit. To be able to access the content of the message, the recipient must provide the server not only its identifier, as for any current messaging system, but also a single authenticator with a same material subject that was used at the time the sender created the message. A single authenticator of a material subject may be one or more image(s) of the authentication region of the material subject or any metrics taken from said image(s) and partly characterizing the microstructure of the material subject.