[cyarvin]

1. People learned (grudgingly) to use spam filters with their email because they had an existing service which had achieved large-scale network effect in a spam-free environment. A new service which develops a spam problem before it achieves critical mass is much more likely to be abandoned.

There must be some reason we haven't seen successful new decentralized service protocols on the Internet since the early '90s. I don't know of a more obvious one.

You can see the issues with StatusNet and spam:

https://www.google.com/search?q=statusnet+spam

2. The problem is that contact names propagate outward from the master state where a push will update them. For instance, they get written down on business cards. They also get cached, imprudently but inevitably, in forms that are still digital but don't update properly.

Imagine a protocol that you could use to update your email address this way, and you'll see the problem. In theory, you could design a special SMTP message that would cause all clients to update their address books. In reality this would scale quite poorly and be quite unreliable, leading people to avoid it, leading it to be even more unreliable, etc. Of course, your chances are much better with a bright, shiny new protocol... but still.

[eleventigers]

RE 2. I agree since some servers that you are trying to push your new address may already have changed theirs. What happens then? Do my friends inform me? What if that unreachable server is not connected to my friends in any way?