The earliest documented email from Satoshi Nakamoto. Writing to Adam Back, Satoshi confirmed he was about to publish a paper that built on Hashcash and asked Back to verify the citation form he had drafted:
[A. Back, "Hashcash - a denial of service counter-measure,"
http://www.hashcash.org/papers/hashcash.pdf, 2002]The load-bearing line of the email reads:
I’m getting ready to release a paper that references your Hashcash paper and I wanted to make sure I have the citation right.
Satoshi attached a link to a pre-release draft titled “Electronic Cash Without a Trusted Third Party” — the working title before the manuscript was renamed to “Bitcoin: A Peer-to-Peer Electronic Cash System” for the cryptography mailing-list draft where the abstract appears in its canonical form.
This is the earliest known direct contact between Satoshi and a central cypherpunk figure, and it is one of the primary-source observations underpinning the cypherpunk-independent-arrival analysis. Two days later Satoshi also wrote directly to Wei Dai (see the 2008-08-22 Satoshi → Wei Dai email).