The current trend in clusters architecture leads toward a massive use of multicore chips. This hardware evolution raises bottleneck issues at the network interface level. The use of multiple parallel networks allows to overcome this problem as it provides an higher aggregate bandwidth. But this bandwidth remains theoretical as only a few communication libraries are able to exploit multiple networks. In this paper, we present an optimization strategy for the NewMadeleine communication library. This strategy is able to efficiently exploit parallel interconnect links. By sampling each network's capabilities, it is possible to estimate a transfer duration a priori. Splitting messages and sending chunks of messages over parallel links can thus be performed efficiently to reach the theoretical aggregate bandwidth. NewMadeleine is multithreaded and exploits multicore chips to send small packets, that involve CPU-consuming copies, in parallel.