The invention concerns in particular a system comprising: a first terminal (1); a second terminal (21 or 22 or 23); at least a first messaging system (31 or 32 or 33) able to transmit, to the second terminal, at least the message body of a message (10) from the first terminal; at least one device (4) controlling at least one condition (11), at least once, the said control device allowing the first messaging system to transmit to the second terminal at least the message body of the said message if the condition control result is positive, the said control device preventing the first messaging system from transmitting to the second terminal at least the message body of the said message if the condition control is negative, at least during the time for which the condition control result remains negative; at least one data server (51 or 52 or 53 or 54) external to the control device; at least one link providing communication through the Internet between on the hand the external server, or at least one of the external servers, and on the other hand the control device, the condition control device being designed to: store a message sent by the first terminal; receive at least one item of information from at least one external server; at least partially perform the condition control relating to the said message stored by means of the information received from the external server.