The message was intercepted by the other party. What are the hints?

The message was intercepted by the other party without prompting. If it is blocked by the other party, you don't know, because SMS blocking is the function of mobile phone. Even if it is blocked, you can still receive text messages, but the blocked text messages will be placed in spam messages without prompting. My message is blocked, but the other party will not prompt when receiving the message, so I can't know whether the other party has blocked myself.