My inclusion of directory as a downside of email was a poor choice on my part -- I occasionally get swept up in writing something, and the thought's been kicking around my head for a few days that email is NOT based on a global directory, but a directory of directories, possibly hierarchical. This means that if you want to get something somewhere, as with routing and DNS, you kick it off first in the right general direction -- someone who knows more about such things than you do, at a minimum.

So, you're right, the fact that email doesn't have a global directory is a feature. It's a feature that's underappreciated by a great many folks who've suggested alternatives to email that do rely on grand central unified directories.

Which suggests that an email alternative which has a similar directory-of-directories concept might stand a better chance.

I've been thinking along lines of clustered hierarchies of users, with various trust bases within them. If you wanted clusters of no more than about 50 neighbors (well within a Dunbar exhange), then a hierarchy 6 layers deep gets you to coverage of all of Earth's population (15.6 billion individual nodes). Deeper, cross-linked, or other structures could offer greater depth of address use for individuals.

I've also been wondering if perhaps national postal systems ought to take over electronic messaging. I can hear the screaming already, but with privacy-supporting protocols (including metadata), much of the risk might be mitigated. In particular, I'm interested in addressing the "who are you?" question -- identity, and re-establishing it, is difficult.

I'm thinking that a good reputation system, and perhaps a poll-and-fetch method, rather than a straight delivery, could make email much more resistant to spam.

Under poll-and-fetch, a sender would indicate that it has a message for another party. That party would then fetch the message, should it be interested. Fully vetted senders would have their content fetched automatically. Spam senders would have to sit on their spools and wait for (and support) many individual incoming fetch requests. Spammers identified as such would be identified through reputation systems.

Granularity of reputation might be at IP space, domain, mail host/peer, or individual sender basis.

For many sender/recipient pairs, a strong and clearly positive or negative relation would be established early. The hump is to become known as a trusted sender, for which some sort of trust seed or reputation vouching system might work. I'm still hazy on what might work there.