We study the problem of delivering $m$ messages between specified source-target pairs in a weighted undirected graph using $k$ mobile agents. Each agent is initially located on some node of the graph and it consumes an amount of energy that is proportional to the distance it travels. The goal is to minimize either the total energy consumption or the maximum energy consumption per agent. In both case we consider agents with different rates of energy consumption. In the scenario where we want to minimize the total energy consumption, we provide (i) a fixed-parameter algorithm w.r.t. the number of agents achieving a constant approximation ratio, and (ii) a polynomial-time $O(k)$-approximation algorithm. When the objective function is to minimize the maximum energy consumption, we show that the problem cannot be approximated within a factor better than $\frac{3}{2}$.