BuxtonTheRed

Hop the country, surely?

Part Jetsons, part Wallace & Gromit.

This is already a solved problem from a technology standpoint. Use a Jabber (XMPP) client which supports OTR ("Off The Record") encryption.

To avoid (or at least, massively complicate) the collection of metadata against you when doing that, do it over Tor. Jabber servers can be run as a Tor Hidden Service.

For aggressive local security, boot in to TAILS (Linux live-boot environment optimised for Tor and security) and do your secret comms in there.

I can foresee that any sort of effective central blacklist provider for darkmail will be "Black Warranted" (coerced by super-sekrit NSA/GCHQ/etc. orders) in to listing desirable targets in order to try to deny them use of the system.

I would suggest that at least a little bit of thought be given to this issue though. Maybe allow a recipient server to specify the number of PBKDF2 rounds that have to be applied to the hash of the message, as a proof-of-work / rate-limit thing? (So if I don't care much, 10 rounds. If I'm sick of spam, 10,000. Or whatever. But let the recipient choose.)

I'm tipping my hand slightly here, but the people who really need this stuff genuinely find GPG a massive pain to deal with - and the proliferation of "live-only" messaging solutions (Silent Circle's Silent Text, and OTR-over-jabber-over-TOR) are a pain compared to an "email" asynchronous workflow.

Where were you when you heard of the end of the war and what were your immediate thoughts or first things you wanted to do?