Abstract: A method and device for providing a closed messenger service to a second authority-level user includes receiving, from a first terminal, a first identity of a first authority-level user who invited the second authority-level user, a second identity of the second authority-level user, and information identifying a workspace to which the second authority-level user is invited, transmitting an authorization request to an approver when it is determined that authorization for the second authority-level user is required on the basis of the first identity, and performing a workspace member registration procedure based on the second identity and the information identifying the workspace when receiving an authorization confirmation to the authorization request from a second terminal.

Abstract: A device for retrieving previous chat history from a chat room includes a control module configured to generate a chat history retrieval request, a transmitting/receiving module configured to transmit the generated chat history retrieval request to a server, and to receive, from the server, a previous chat history, and an input/output module configured to display the received previous chat history in a chat window. The invitation message at least includes an ID of the first user, an ID of the second user, an ID of the chat room, a transmission time of the invitation message, and a previous message code. The previous message code is unit time for limiting the retrieval start point.

Abstract: A device for retrieving previous chat history from a chat room includes a control module configured to generate a chat history retrieval request, a transmitting/receiving module configured to transmit the generated chat history retrieval request to a server, and to receive, from the server, a previous chat history, and an input/output module configured to display the received previous chat history in a chat window. The invitation message at least includes an ID of the first user, an ID of the second user, an ID of the chat room, a transmission time of the invitation message, and a previous message code. The previous message code is unit time for limiting the retrieval start point.