We adopt a mechanism design approach to model communication between a principal and a privately informed agent in the context where monetary incentives are not available. We provide a simple condition on the distribution of the agent's type which ensures that the optimal mechanism is continuous. With strict log-concavity of the distribution, there exists a unique optimal mechanism that is characterized.
Martimort, D., & Semenov, A. (2006). Continuity in mechanism design without transfers. Economics Letters, 93(2), 182-189. https://doi.org/10.1016/j.econlet.2006.04.011 (Original work published 2006)