Email doesn't require DNS. Modern spam solutions for DNS do. You can most definitely use something like `spiped` to create a mutually authenticated, secure channel over IP, and just send mail over that. Or build a VPN overlay network and send mail to raw IPs. If you're going to cloister yourself with your fellow monks^W nerds then this is simple.
Hm, I think my point might not have been clear enough. I would find it hard to function without interacting with central system, like sending an email to someone on gmail. Just today, I emailed a plumber on gmail, but it could easily have been an old friend or a relative or whatever.
They will take the loss.