Fastmail created the JMAP Standard, published by IETF. Take a look here: https://jmap.io/

Web mail can replace IMAP/POP, but you're still going to need an SMTP server to receive email. Or is there some sort of widely supported SMTP over HTTP protocol that I'm unaware of?

Webmail replaces both IMAP/POP and SMTP for the connection between the user and the mail service they are using. The connection between you and a webmail provider is just a simple HTTP/S web application. It’s the connection between your mail service and the recipient’s mail server that will use traditional mail protocols.

I am aware of that, but you're missing my point. Webmail needs SMTP (while it doesn't necessarily need IMAP/POP). So there is bound to be an SMTP server somewhere that cannot be hidden in HTTP traffic, which is what I think hansel_der was implying.

Well fastmail's servers are not in Russia, so they can just keep using SMTP without issue, it would only be the client in Russia who would need to tunnel his traffic to fastmail.

You're forgetting the SMTP server on the other end. If Fastmail SMTP servers can no longer relay messages from/to Russian SMTP servers, then Fastmail is no longer a viable email service for Russians communicating with each other, unless all of them were using foreign based email services.

I am not forgetting anything. It is indeed true that fastmail is broken for Russians in Russia. And trying to tunnel out to fastmail just to mail back in to Russia makes little sense.

Also broke are all Russian email users who have to send to or receive from the free worlds fastmail accounts. Would seem this is just Russia damaging Russians.