- Even if it were true that "everyone uses Google/Microsoft/Apple/etc", the ones that don't can still send/receive emails from everyone else. - If one of the of the big providers disappear, the system as a whole will continue to function.
As for the few that do have the capacity to setup a mail server, they would only be able to message others that also have the capacity to setup a mail server (again we're assuming no centralized providers and thus no delegation of this task to a trusted party). So maybe the system would still work for this niche group... but then we get into the bigger question: are there entities today that control the Internet and do they have the capacity to shut down systems like email? Tor?
Call him up on the phone or message him on whatsapp or... whatever...
email IS decentralised. Even if we had ONLY gmail, a startup could implement a better email frontend and be successful.
The fact that you don't get to talk with other people only because an big email provider would disappear does not change the fact that email messaging systems are designed to be inter-operable. That is the key point. To try to argue otherwise is insane.
No, it's not the case that "everyone" does that. I don't, and many of my colleagues don't. Perhaps muggles in general don't, and perhaps you're really only talking about such non-technical people, but your hyperbole undermines your argument.
And I'm getting really tired of those big services automatically classing as spam anything that comes from a different domain.
To add a little more nuance to that, millions (or billions?) of people working in various areas have email addresses provided by their employer with specific domain name suffixes. Even if those are using cloud based email providers like GSuite or Outlook 365, as far as someone who wants to correspond by email with these people is concerned (personal or work use), the email address is certainly not an @gmail.com or @outlook.com address. And all these people understand that quite well, even if they don't work in the tech sector.
> And I'm getting really tired of those big services automatically classing as spam anything that comes from a different domain.
This really bugs me A LOT! It's as if the systems have a knee jerk reaction based on domain names while they themselves wouldn't consider all their users (on their domains) as spammers.
This is a totally different story for Facebook.
EDIT: I don't think people will be able to abandon email, given it's a replacement for paper mail (banking, official papers, etc). If the big players won't play nice, people will need to get to another provider, simply because the source of email won't be willing/fast enough to jump on [system X].
Mostly everyone, but not everyone.