That brings up another point. How important is iMessage in China? The iPhone’s market share in China is small and statistically when you’re using iMessage you would probably be sending a message to a none Apple device over unencrypted SMS.

Email is the least secure method of sending data and always has been.

I’ve never paid attention to it until now, but you can selectively disable iCloud backups for any of the built in apps and third party apps in settings.