What is the MO ACK FLAG option?

Do not use unless you are 100% certain that you must use it. Very soon it will only be available only if
using direct IP. When this option is used, the device sends a message to the gateway and the gateway
will queue up the message for delivery to a direct IP server. Once the direct IP server receives the
message, the gateway will not consider the message delivered until the direct IP server responds with a
line of code to say the message has been delivered. This means that if the direct IP server does not
respond with this code, the gateway will continuously send the message over and over again.