Method of transmission of an electronic message by a sender to a recipient comprising the following steps: - initially, choice by the sender of at least one material subject having at least one authentication area showing a microstructure at a given observation magnification, then acquisition or implementation of at least one first image of the authentication area, - recording, by the sender, of the electronic message to be transmitted on a server system, - determination from the first image of a first unitary authenticator of the material subject and registration on the server system of the first unitary authenticator, the first unitary authenticator being associated with the message to be transmitted, - recording on the server system of an identifier of the recipient of the message, the identifier being associated with the message to be transmitted, - notification to the recipient of the existence of a message, - transmission to the recipient of information relating to the material subject whose image of the authentication region is to be used by the recipient for the retrieval of the message, - acquisition by the recipient of at least one second image of the authentication area of the material subject, the second image being acquired with a quality substantially equivalent to that of the first image so that the first and the second images contain a substantially equivalent level of information relating to the authentication area, - determination from the second image of a second unitary authenticator of the material subject, - transmission to the server system of an identifier of the recipient who acquired the second image from which the second unitary authenticator originated, the identifier of the said recipient being associated with the second unitary authenticator, - comparison of the unitary authenticators, - in case of similarity between the first and second unitary authenticators and matching between the recipient identifier recorded in the server system and the transmitted recipient identifier, transmission to the recipient of the message associated with its identifier and with the unitary authenticator. - initially, choice by the sender of at least one material subject having at least one authentication area showing a microstructure at a given observation magnification, then acquisition or implementation of at least one first image of the authentication area, - recording, by the sender, of the electronic message to be transmitted on a server system, - determination from the first image of a first unitary authenticator of the material subject and registration on the server system of the first unitary authenticator, the first unitary authenticator being associated with the message to be transmitted, - recording on the server system of an identifier of the recipient of the message, the identifier being associated with the message to be transmitted, - notification to the recipient of the existence of a message, - transmission to the recipient of information relating to the material subject whose image of the authentication region is to be used by the recipient for the retrieval of the message, - acquisition by the recipient of at least one second image of the authentication area of the material subject, the second image being acquired with a quality substantially equivalent to that of the first image so that the first and the second images contain a substantially equivalent level of information relating to the authentication area, - determination from the second image of a second unitary authenticator of the material subject, - transmission to the server system of an identifier of the recipient who acquired the second image from which the second unitary authenticator originated, the identifier of the said recipient being associated with the second unitary authenticator, - comparison of the unitary authenticators, - in case of similarity between the first and second unitary authenticators and matching between the recipient identifier recorded in the server system and the transmitted recipient identifier, transmission to the recipient of the message associated with its identifier and with the unitary authenticator.