Mobile software agents require a distributed execution environment in which they can command the use of many resources like memory, CPU time and bandwidth. While current research seems to concentrate on roaming agents at the application level and tries to define suitable high–level environments, we think that such an execution environment must be rooted at a very low-level. We argue that these environments have very in common with distributed micro-kernels, and that therefore one should position them even below current operating systems. In this paper we report on the implementation of such a micro-kernel built for communications messengers (messengers are autonomous threads of control that can travel through the network: they are the low-level elements from which higher-level agents can be built). We present our viewpoint and describe the current state and some implementation considerations of our Messenger Operating System prototype MOS.