I was thinking of push notification data and skipping several other significant partial leaks. After a little research, I think I overstated the push data leak, though it’s still significant. Anyway, framing it as copies was a rough approximation, the issue is many high probability partial copies resulting in virtual certainty of unencrypted access to any desired data.

iMessage leaks I know about:

- iCloud backups. While I appreciate Advanced Data Protection, I still count this because it’s not available everywhere, most people have it off, and most people with it off are unaware of it backdooring the E2EE marketing they still saw.

- Recipients’ copies, and all the ways their copies get copied. Yes, tricky to address, that’s the comment. While no app can guarantee no unencrypted recipient copies, privacy focused apps do make it not happen unintentionally and by default.

- APN leaks the timestamp, sender, and recipient of every message. Especially powerful in combination with recipient copies.

- Apple controls the key directory and can MITM at will. As usual, see Signal for a high profile attempt at a centralized key directory that’s resistant to controller abuse.

- Contacts, Siri, and Apple Intelligence all ingest then upload iMessage data.

- No source code or reproducible builds. Obvious reasons, still a real hole.

The other person's iCloud backup I assume.

Avanced Data Security keeps your copy in iCloud safe, but doesn't help with the people you are messaging's copy.

If you live in the UK you can't enable ADS at all, apple cares about your privacy but not enough to piss off the UK government it seems.