Delay-tolerant networks often adopt the message replication methodology to increase the opportunity that destinations can receive messages from a source node in a network. Repeatedly replicating messages, however, consumes significant resources such as local buffer space on nodes and internode communication bandwidth. Previous buffer management and scheduling policies mainly contributed to a simple scenario of message unicasting from a source to a singular destination in a network. When message multicasting toward multiple destinations is considered, previous solutions perform inefficiently. This paper proposes a new buffer management and scheduling policy for message multicasting in delay-tolerant networks. The proposed policy is an optimal-based design with a new utility function, which can prioritize messages in a buffer for maximizing the successful delivery rate in a network. Simulation results manifest the efficacy of the proposed scheme under different mobility benchmarks in delay-tolerant networks.