This seems reasonable, and even achievable. It's probably already possible to reject emails that don't have SPF and DKIM (to prevent spoofing), so we just need a way for a sender to determine whether the recipient has whitelisted them. If they haven't been whitelisted, they should be limited to sending a short (100 character?) plaintext introduction, with no hyperlinks.
> to be invoked as needed for sensitive data. 98 percent of email doesn't need encryption --- but that last 2 percent does.
I disagree slightly. The 2 percent that does need encryption also requires that the other 98 percent be encrypted too, so that:
* attackers don't know which messages to target,
* the pattern of encrypted vs. unencrypted emails doesn't reveal information in itself, and
* the user doesn't have the mental overhead (and error potential) of having to decide which emails are worthy of encryption (a task which requires them being able to reliably predict the future).
Much of the logic for encrypting the whole of the web (as opposed to just "important" pages) applies to the need to secure (almost) all email too. The main difference, I think, is that the web is a pull architecture while email is push, meaning that spam and identity works differently, and server-side filtering can't work with E2E encrypted email.
Revealing my email as a potential target is a minor trade off I would accept for ease of use. It should not be a big deal if the encryption is solid. The cost to try and break the encryption is enough to discourage most attackers.
How many email "man-in-the-middle" privacy breeches are you aware of? The ones I am aware of usually happen at a service provider endpoint --- like Google data mining your email. I doubt even Google is motivated enough to absorb the cost of breaking email encryption. There would also be legal ramifications if they (or any other provider) did.
But that's the problem, how does a decision-fatigued user decide what is and isn't sensitive? People have lost jobs over tweets they sent years ago, and we know that users get used to clicking through warnings and find it difficult to tell whether something is secure or not. Dutch Jews filling in the 1930 census form didn't realise that stating their religious affiliation was going to prove a disastrous decision a few years later.
> How many email "man-in-the-middle" privacy breeches are you aware of?
There are all sorts of targeted security attacks and privacy breaches I'm not personally aware of, but protecting all email from potential snoops is the right thing to do regardless of how often they happen.
A totally private (white list only, friends and family) email address would be very attractive to a lot of people.
Lots of people would want 2 email addresses with varying levels of restriction --- one public and one private. I do this now but my private address is lacking any strict control to keep it this way.
If that were true, mail providers would already offer this. In fact, I suspect some unsophisticated ones probably do, with all unrecognised senders having their emails sent to the recipient's Spam folder, with a few exceptions for DKIM-signed mail from frequently seen addresses, like Amazon receipts.
Appeal to Authority?
If people truly had any interest in an email replacement, mail providers would already offer this. So why are you asking your original question?
https://www.thoughtco.com/logical-fallacies-appeal-to-author...
No, appeal to the market. If there is demand for a product in an interoperable market, then one would expect an entrepreneur to create that product. (Admittedly, the unusual economics of email services mean that market forces might differ from theoretical models, but there could still be some pressure for competing providers to add features that users want).
> If people truly had any interest in an email replacement, mail providers would already offer this.
There are dozens of replacements for (some aspects of) email, including WhatsApp and Twitter. To be fair, these services do (I think) have mechanisms that effectively limit your interaction to just people you already know, but the fact that email still exists (and doesn't have this restriction) suggests that there is value in the openness that it offers.
Privacy.
If someone sends me spam, I want the ability to easily reject any further mail from either the specific address or the entire domain. It would be nice if this applied universally, on every device. Basically, a user controlled spam filter at the server.
Also, a standardized form of encryption --- to be easily invoked as needed for sensitive data. 98 percent of email doesn't need encryption --- but that last 2 percent does.
Basically, privacy invasion via email needs to be eliminated.