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Delay Tolerant Network (DTN) is a kind of network that there is no continuous network connectivity among nodes. There are no end-to-end and constant connection paths from source nodes to destination nodes due to the mobility nature of nodes. In such networks there exists an inevitable long delivery delay. DTN is designed to perform properly over intermittent connections among nodes. Because of mobile nature of nodes, routing in DTN is based on store-carry-forward patterns to forward messages. Store-carry-forward is based on appropriateness of next node to deliver the message. Improving performance of such networks depends on both routing protocol and buffer management policy when nodes have limited buffer space. However, by sending multiple messages to a node, the number of received messages may exceed the capacity of the nodes and cause a buffer overflow. In order to increase performance, we have to drop some messages and receive some new one. Dropping appropriate message is a challenging problem. Deleting an appropriate message and replacing with a message with better condition can leads to increasing delivery ratio and decreasing delivery delay. Recognizing message with better condition is another challenge. So an efficient buffer management is very important to improving routing performance. Most buffer management policies are mainly for routing protocols. In this paper, we propose a buffer management policy for RPRTD routing protocol in delay tolerant network. This approach is based on Remaining Time to encounter nodes with the Destination node of messages (RTD). This algorithm determines which of the messages should be transmitted, which of the nodes should be considered as sender and which of the messages should be dropped when the buffer is full. Simulation results show that proposed algorithm has improved the delivery ratio and delay in delivering messages compared to the state of the art.