Distributed Embedded Systems (DES) typically have real-time and dependability requirements. Moreover, if they have to operate in dynamic operational contexts, they need to be adaptive. That is, they must be able to automatically and autonomously rearrange in response to changes. In order for a DES to be adaptive, its underlying subsystems must be flexible. The implementation of the flexibility, just like the implementation of the real-time and dependability, cannot be done in an orthogonal manner since it entails the collaboration of various subcomponents at different levels of the architecture. The DFT4FTT project proposes a self-reconfigurable infrastructure for implementing DES with real-time, reliability and adaptivity requirements. One of the most relevant fault tolerance mechanisms is the dynamic replication of messages, that makes it possible to tolerate transient faults affecting the network. In this paper we describe more in-detail the design and implementation of this mechanism.