Today's systems are often distributed, and connecting their different components can be challenging. Message-Oriented-Middleware (MOM) is a popular tool to insure simple and reliable communication. With the ever growing loads of today's applications, MOMs needs to be scalable. But as the load changes, static scalability often underuses the resources it requires. This paper presents an elastic message queuing system leveraging cloud's on-demand resource provisioning, which allows the use of just enough resources to handle the current load. We will detail when and how provisioning decisions are made, and show the result of our system's evaluation on Amazon EC2 public cloud. This work is based on Joram, an open-source JMS compliant MOM and is now part of its distribution on OW2 consortium's website.