Today mobile devices can interact with their environment through wireless communication. Wireless communication has a limited communication range, which introduces two major problems, currently not captured in distributed middleware. Firstly, they are less reliable and secondly they are extremely dynamic. Both problems complicate the development of mobile software. In this paper we extend the operational semantics of the actor model to capture these two properties by adding a single new concept to the model: the mailbox. This paper provides a foundation for new implementations of the actor language and frameworks that are usable in the context of mobile ad-hoc networks.