I like this idea and think it has legs. But, eventually it might be worth rewriting daemons for SMTP/IMAP that have a simple config file format that would allow simple white/blacklisting domains such that one could run a server that would reject all emails from any domain other than the 6 one specifies. Further, without pgp encryption/signing msgs are discarded.

I think such an approach could be interesting, but it seems there is a need for a non-profit to govern such a thing.