A message intermediate event can be used to both send and receive messages. The event marker must be filled when used to “throw” the message (see the upper figure on the right). If the process was waiting for a message, this causes it to continue, or it changes the flow for exception handling.
1] Silver, B. (2009). BPMN Method and Style: A levels-based methodology for BPM process modeling and improvement using BPMN 2.0. In CodyCassidy Press US.