“BTW, end-to-end (E2E) encryption does not in itself guarantee that your data is encrypted at the vendor’s facility (data at rest). E2E is about the transmission, with a sender and a recipient who can both read the data, and thus allows the vendor to store plaintext after decryption at their facility.”
The want for convenient “storage” is the whole big deal... Laziness.
All this is why I am getting off the WWW/HTTP protocols altogether. True encrypted TLS end to end P2P with no intermediate peer network node hops. Basically phone number directly to phone number with no “message service” in between. No storage at all except your local client tunneled to the end receiver’s local client. And which is fine, like a FAX machine it will just have to redial occasionally until the machine on the other end is online and available then it will send and they will get it.
This want for “convenient second party storage” is what has created all these email problems. Want to be secure? Get “FAX mind” and just keep dialing until their FAX machine (local Client inbox) picks up the phone on the other end. Then it is tunneled directly from machine to machine. But this is too much “Work” so now we have what we have now... A mess of third party intervention, control, and stewardship. There are local email clients that will automatically check for a connection every so often until the direct line becomes available to receive like a FAX machine does.
This is true end to end encryption.
The price of internet communication is eternal vigilance.