for some reason people are unwilling to imagine an email system in which an ISP will only accept incoming messages from another ISP with which they have an existing agreement, i.e. rather like email peering.
You say this as if it's surprising that people are willing to accept communications from people they have not yet communicated with before.
There is a difference between an ISP and a person who sends or receives email. I am only suggesting that ISPs should make mail peering agreements, not individuals. When I wrote a weekly column for Internet World magazine, I frequently received email from readers with whom I had not previously communicated because my email address was printed at the bottom of each article. I developped my suggestion with this in mind. Anyone will be able to write an email and relay it through their ISPs authenticated submission port regardless of whether they are at home or in a hotel in some other country. If their ISP has a mail peering agreement with my ISP, then it will be relayed directly to them. If not, then they will relay it to a larger email peer who can handle the mail routing. Clearly, there has to be some way for a domain to publish their email peers in DNS so that mail routing can take place, but this is relatively trivial as are most of the technical issues. The bug problem to solve is the operational issues of putting it all together and negotiating mail peering areements.
The world is not like your gated community.
I have never lived in a gated community. Also, this new email architecture would not be a gated community. It may start off as a special service offered by a few larger ISPs to business clients, but over time I think most people will migrate to it. --Michael Dillon