

I don’t see how you wouldn’t have your email on an email providers servers - that’s how email works. You send an email via a provider, they forward it to the destination address you’ve included with the email.
That destination address is another email provider’s server, which holds it until the receiver connects and downloads it. Email is a store-and-forward system, designed at a time when users weren’t always connected. It still works this way.
Email is old, so the fundamental mechanics are pretty simple, and encryption wasn’t an option at the time - so it’s sent in the clear. Otherwise it would require both sender and receiver (either at both ends, or the servers) to agree on an encryption to use.
Yep.
Rather than try to single-handedly re-engineer an old protocol to be secure, I just use it for stuff where security isn’t a big deal. Including messages with links to secure resources (and send credentials via a separate system).