Sunbird just relayed messages back and forth using a Mac mini in a warehouse. They probably had something that read the messages app on there and sent to their app on the phone through their servers, and seemingly forgot to encrypt anything during this process.
This is actually sending messages as iMessage. It’s been reverse engineered which is an incredible feat, iMessage has been out like …10+ years? And no one figured it out yet until this 16yr old rocks up.