What does it mean to send a message to a friend on an Apple 7 mobile phone unless the recipient adds my ID to the address book?

You are not in the other party's address book, so you can't send it.

Solution:

1, let the information receiver add his phone number to his "address book".

Ask the receiver to send me a message to start the conversation.

3. On my device, go to Settings-Messages-Send and Receive, and make sure that only my phone number is selected under "Use when starting a new conversation". If you select "My Apple ID", the information will be sent as spam.

IPhone 7 has rose gold, gold, silver, black, bright black, red and other colors; Built-in stereo speaker, the sound will be more surrounded and the volume will be greatly improved; Adopt A 10 fusion processor, and the other two cores are high-performance cores, which can save power1/5; The Home button supports pressure sensing.