Rules have two parts: a schedule and a condition. The schedule defines when an event is to occur. The condition defines which messages are to be part of the event. For example, if the event is message transmission, then the schedule indicates when transmission will occur and the condition defines which messages will be included in the transmission. If the event is message deletion, then the schedule indicates when deleting will occur and the condition indicates which messages will be deleted.
Each rule has the following form: