The "postal" model of communication [3, 8] T = a + ßn, for sending n bytes of data between two processes with latency a and bandwidth 1/ß, is perhaps the most commonly used communication performance model in parallel computing. This performance model is often used in developing and evaluating parallel algorithms in high-performance computing, and was an effective model when it was first proposed. Consequently, numerous tests of "ping pong" communication have been developed in order to measure these parameters in the model. However, with the advent of multicore nodes connected to a single (or a few) network interfaces, the model has become a poor match to modern hardware. In this paper, we show a simple three-parameter model that better captures the behavior of current parallel computing systems, and demonstrate its accuracy on several systems. In support of this model, which we call the max-rate model, we have developed an open source benchmark1 that can be used to determine the model parameters.