This exit is taken from the JES2 main task, from the HASPWQUE (special purpose CMB queuing) routine of the HASPCON (console support services) module, for all JES2 main task $WTO messages. The exit occurs at the beginning of HASPWQUE, after the $WTOR routine has processed the $WTO macro and before HASPWQUE queues the CMB containing the message for transmission. If, by passing a return code of 0 or 4, your routine allows the message to continue, control returns to HASPWQUE, which then queues the message for transmission. If, however, your exit routine cancels the message by passing a return code of 8, the transmission queuing performed by HASPWQUE is bypassed and JES2 gives control to $FRECMBR, the $FRECMB service routine.