Will the SMS sent by Apple's mobile phone be blocked if it is not delivered? But the incoming number can be connected.

If you send an iMessage (blue message box), it will be "delivered"; If you send a short message from the operator (green message box), it will not be delivered; Because iMessage is sent through the network, you can return "sent" through the network, but the operator's short message Apple can't return this prompt, so people can't waste your phone bill and return it at will ... so the conclusion is: no congestion.