We develop a system dynamics model of message-based communication, where the information-processing capacity of message recipients is limited. Profit-seeking broadcasters send messages, but only some of these messages are valuable to recipients. Recipients cannot determine whether or not a message is valuable until it is processed. Information overload occurs when more messages arrive than recipients can process. Numerical experiments test alternative approaches for mitigating information overload. We show that message filtering can increase the flow of for-profit communication. Market-based mechanisms, while aimed at improving the social outcome, can actually lead to suboptimal results and to a complete collapse of for-profit communication...