  A snap-stabilizing algorithm ensures that it always behaves according to its
specifications whenever it starts from an arbitrary configuration. In this
paper, we interest in the message forwarding problem in a message-switched
network. We must manage network ressources in order to deliver messages to any
processor of the network. In this goal, we need information given by a routing
algorithm. But, due to the context of stabilization, this information can be
initially corrupted. It is why the existence of snap-stabilizing algorithms for
this task (proved in [CDV09]) implies that we can ask the system to begin
forwarding messages even if routing tables are initially corrupted. In this
paper, we generalize the previous result given a necessary and sufficient
condition to solve the forwarding problem in a snap-stabilizing way.
