Earlier quoted context omitted.
Apple’s own transparency report. Look at the FISA (FAA702, aka Prism) section. Per the Snowden slides, this (FAA702 collection) is the #1 most used collection method by US spies. They can basically read approximately every camera roll and iMessage in the country with a few clicks.
So, seems that E2E is a total bullshit then?
All of the iMessage access data (either the iMessages themselves or the iMessage sync key for “Messages in iCloud”) is stored in the non-e2ee iCloud Backup.
This means that the iMessage service e2ee is meaningless because the iMessages themselves are not e2ee.
Note well that turning on iCloud e2ee is insufficient, as everyone else that you iMessage with will still have it off, and all of your iMessages will still be backed up non-e2ee to Apple in their device backups.
Having iCloud e2ee available is the best of both worlds for Apple: they can say that it’s available for privacy-conscious users to opt into, while still being able to turn over basically 100% of all iMessages to the feds whenever they ask.