A disclosed control system configured to control transmission of content data between communication terminals includes one or more processors, and a memory storing instructions that, when executed by the one or more processors, cause the control system to receive a transmission request including attribute information indicating an attribute of the content data for transmitting the content data from a first communication terminal, and perform control for transmitting the content data to a second communication terminal specified based on the destination information in response to the attribute information being in a predetermined format, the predetermined format including destination information indicating a destination of the content data and to perform control for transmitting the content data to a third communication terminal that has requested reception of the content data having the attribute indicated by the attribute information in response to the attribute information not being in the predetermined format.