A method and apparatus for processing message is described. In one embodiment, an application programming interface is configured for receiving and sending messages. A message credit account of a sender is maintained. The message credit account of the sender is debited when a message is received from the sender to a receiver. The message credit account of the sender is credited when a replenishment message is sent to the sender in response to the receiver processing the received message. The sender is prevented from sending any messages to the receiver when a balance in the message credit account of the sender becomes negative.