IMessage Spammers Batter Apple Users in China

Alternatively, you can kill iMessage alerts from all senders who aren’t in your contact list (Settings > Messages > turn on “Filter Unknown Senders”). You can still read the filtered messages by going to the “Unknown Senders” tab in iMessage.

If you want to report an iMessage spammer to Apple, you can click on the “Report Junk” link under the message.