It's worth repeating here.
I think the first steps should be pretty clear:
(1) New internet over old internet. Like IPv4 over IPv4, we should be able to connect to the new network over the infrastructure of the old. That doesn't mean that we have to use the old infrastructure, but that we can if we have the capability and inclination. This is necessary for mitigation and/or migration.
(2) Tor-ified e-mail. It should be a simple matter to set up a mail client that works over Tor and that incorporates full public key encryption. It might take some jiggering, but you should at the very least be able to set up a makeshift listserv that has RSS feeds that update with the latest messages. Publish it on your computer in an RSS feed the listserv is set up to check, cryptographically sign it and encrypt it with their public key, and the listserv decrypts it, reencrypts it with each recipient's public key, and the recipients retrieve it via RSS password protected by HTTP basic access authorization. You now have a message that you can be sure came from the sender and has not been tampered with--so if it's spam, you know who the spammer is, and you do not know who is sending messages unless you're the recipient. You would probably also want a list of message-IDs for the messages downloaded to be kept on each recipient computer, so that the messages can be removed from the queue once the other computer receives them. I'm sure this could be streamlined, but this method works now.
(Please do not construe this opinion as representing that of my employers)