Quantum dialogue is a type of quantum communication in which users can simultaneously send messages to each other. The earliest instances of quantum dialogue protocols faced security problems such as information leakage and were vulnerable to intercept and resend attacks. Therefore, several protocols have been presented that try to solve these defects. Despite these improvements, the quantum dialogue still faces some challenges. Currently, the limited number of participants and the impossibility of expanding users during the conversation are among the most important challenges of this kind of protocol. In this research, we have designed a multi-user quantum dialogue protocol that solves the mentioned challenges. The proposed protocol is a generalized type of quantum dialogue in which users can communicate simultaneously. The number of participating users is not limited and can be changed dynamically (i.e. without the need to restart the protocol). It means that, during the execution of the protocol, a user can leave the conversation, or a new user can join it. Communication between users is established through a central semi-trusted server. The investigations show that the proposed protocol does not have information leakage. In other words, no unauthorized entity (not even the intermediate server) can access the raw data exchanged between users.