[cranekam]

> How can you guarantee this?

I mean, I can't guarantee it. As others have said, it's not impossible that things have changed since I left or will change in the future. But I doubt it — e2e encryption is a big selling point for WA and something that is dear to the company's heart.

> And how about received messages?

It's the same deal — the sender encrypts the message with the the recipient's public key, and the recipient decrypts it with their private key (which was generated locally and never goes over the network).

> How can you retrieve all your old messages/conversations when you install the app on a new device? Don't they come from WhatsApp servers?

No, you can only get old messages from your old device or from a backup that went to the cloud somewhere (e.g. iCloud or Google backup). The messages on your phone are stored locally in a DB, so if you copy that DB to a new phone it'll have the new messages. WhatsApp doesn't store messages — they are only present on WA infra until acknowledged as received by the destination.