While the client computer is offline, the application can still send and read messages from its local queues. Messages sent while a computer is offline are stored locally and sent to their final destination when the client computer is reconnected to the network.
When a message is sent, its message timers (time-to-reach-queue and time-to-be-received) start ticking as soon as the send operation succeeds, even if the client computer is offline.
Caution Messages must be sent in recoverable mode if the offline client computer is to be turned off. Messages sent in express mode are held in RAM and will be lost when the computer is turned off. To send recoverable messages, set the delivery property (PROPID_M_DELIVERY or MSMQMessage.Delivery) of the message to MQMSG_DELIVERY_RECOVERABLE.