If you want to send the SMS later or write more SMS and send them all at once, you should press the QUEUE button instead of the SEND button.
Every message in the queue will be sent by pressing the SEND button. You will be asked if you want to send the failed messages again.
You are able to edit or delete messages or recipients by selecting a row from the queue. Press the left mouse button to select the row and then press the right mouse button tho select what you to do with.