> First-contact consent: an unknown sender doesn't get into the mailbox; they land in a "requests" box with their first message visible (like Signal's message requests). You accept, and the thread opens forever. A stranger can knock on your door, which is the essential property of mail, but they can't fill up your living room.

I like this.

Question: can this e-mail specification/implementation also replace direct-messaging protocols (like WhatsApp)?

I'm very excited by this idea. I feel like email/chat is ripe for reinvention.

I don't agree with "Domain control as a fallback", as the author said "a domain is not owned, it is rented" and I want to normalise the idea that if you lose your private key, you need to start again. I hate that we keep giving so much authority to domains, it's such a big weakness. The author even left the key rotation chain out of the initial implementation.

I still think root/signer keys or sigchains are decent options.

I think the network effects make email hard to replace, virtually everyone online has an email address. If this could include a migration path, with backwards compatibility with SMTP, I think it would have a better shot of getting adoption.

Modern email already depends on HTTP, with protocols like MTA-STS (https://www.rfc-editor.org/info/rfc8461/) using HTTPS/TLS to improve transit encryption, or Web Key Directory (https://datatracker.ietf.org/doc/draft-koch-openpgp-webkey-s...) which uses HTTP for key distribution. Personally I think these incremental improvements of SMTP are more promising than replacements, but we deserve better email however we can build it.