A system for filtering electronic messages includes a client machine that includes a security module, wherein the security module has access to at least one message sent by a sender identified in the message through respective identification data and received by the client machine, wherein the security module is configured for reading the sender's identification data from the header of the message, finding and storing any potentially harmful contents of the body of the message, verifying if said potentially harmful contents satisfy validation conditions which are specific for the sender having the identification data specified in the header of the message, allowing or denying access to at least part of the body of the message, in which the potentially harmful contents are present, based on the result of the verification.