Disclosed is a method and system in which an intermediary is provided within a communication path through which a message is transmitted from its originator to a client device, and the intermediary operates to insert into the message a target port number based at least in part on the originator of the message. In a scenario where the message originator provided or is otherwise associated with a given application group on the client device, the intermediary may thus modify the message to have the message designate as target port number the port number that the client device associates with the application group. Ultimately, when the client device receives the message, the client device would read the target port number and responsively route the message to the appropriate application or application group.