Email these days is however tied to DKIM and domains. We have UI problems, but communicating to a companies email servers at their domain name can be reasonably expected to be communicating with that company.

It's just the security story on that if you never want the content disclosed isn't great, but conversely, conceptual entity communications are always going to be a bit public by nature.

There's a whole other rant I have about this problem, where we really lack domain specific trust standards - i.e. communicating with a business, what I want to know is "is this a recognized legal business entity in it's jurisdiction, and what's it's status to mine?" which is very different to "I need to make absolutely sure me and John Smith's communication is just between us" - but they're in the same space of problem.