A 5 email historical exchange between Back and Nakamoto was entered into the court records of the COPA vs CSW case today. Pete Rizzo's twitter thread has all 5 emails pictured and some commentary from him.

The first email was sent by Nakamoto to Back on August 20, 2008, checking he had the citation to Back's hashcash paper right and giving a brief précis of his own forthcoming paper and a link to a pre-release draft.

August 21 : Adam replies, and suggests Nakamoto look at Wei Dei's paper on B-money.

Nakamoto writes back, saying he wasn't aware of Wei Dei's paper. After having now looked at it he says : "Thanks, I wasn't aware of the b-money page, but my ideas start from exactly that point." (Satoshi will go on to add this paper to his citations in Bitcoin's white paper.)

Adam writes back a second time, saying that he still hasn't looked at Satoshi's draft but suggests another paper he might like to look at, "by Rivest et al called micromint".

October 1st, 2008 : Nakamoto writes to Back for the final time, thanking him again and announcing the release of the first public implementation of Bitcoin (v0.1). He quotes an overview of the project by Hal Finney from a discussion on the Cryptography mailing list.

The exchange stops there, as Back doesn't reply further and quoting Rizzo "According to Adam's public statements, he wouldn't look at Bitcoin again until late 2012."