[hudon]

If all centralized providers disappeared and I had to send a message to my friend, I wouldn't setup my own SMTP server... I'd just send him an iMessage. Or I'd post to a Slack group. The system without centralized providers is useless to most people using it today because no one wants to learn how to setup a mail server when there are dozens of alternative messaging tools.

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?