Re: The hardware underneath
The big thing Facebook, Google etc bring to the table is a huge network of maintained servers
That's only part of it. Orlowski's "trivially simple" comment is, in fact, quite wrong. More is different.
When you scale up a system to the kind of transaction rates that Facebook handles, you need quite a lot of non-trivial software. It's not just a question of throwing hardware at it. Even a very low failure rate1 turns into quite a lot of failures when multiplied by that load.
The big social-media players do quite a lot of software R&D. It is not trivial, nor simple.
And yes, Dovecot may handle, in aggregate, the email of a couple of billion people. Email workloads are orders of magnitude smaller than social-media workloads.
I'm perfectly happy to see people extending IMAP (though I've never been a fan of IMAP, particularly) or other open protocols. I've spent much of my professional career working with both open and proprietary data-comm protocols, and even the gnarliest open ones (IIOP, say, or if you want an IETF-blessed example, Telnet) are generally much nicer than the proprietary alternatives (ah, SNA, so many years you have claimed). But minimizing the technical challenges helps no one.
1And the high tolerance for failure in social-media applications, which really don't care about consistency and reliability.