Encryption is irrelevant here. Even if it was kept fully server side, the actual issue is that they allow starting a conversation in a strong model and continuing it in a weaker one. Disallowing that entirely would be a huge hit to user experience.
replyThat's not a trivial thing to do for them because they offer zero data retention environments to enterprise clients.
replyThey can always keep the encrypted blobs server side and send the key to the user. But regardless, that isn’t going to help with this issue (see my comment above).
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