Aggregation process status. One of: ready: The number of messages can be obtained. unready: We haven’t finished calculating the number of sent messages for the specified in date. For example, this property is returned when the delivery date or a future date is specified. Calculation usually takes about a day. unavailable_for_privacy: The total number of messages on the specified day is less than 20. out_of_service: The specified date is earlier than the date on which we first started calculating sent messages (March 31, 2018).