Further in the thread:

While the email is not signed, and there are a number of PGP keys listed on key servers for him (to vary addresses), he didnt sign any emails with any PGP keys.

https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015...

I've researched this for a long time; for many reasons, I believe it's him. He never cryptographically signed anything, so the lack of signature actually weighs in favor of the message's authenticity -- not against it.

"Something I only recently realised is that Satoshi's apparent policy(1) of never making any cryptographically secure signatures to link together his posts - or indeed any communication at all - fits well with the avoidance of creating a central authority figure. ... As you've often said, the biggest achievement by Satoshi in the creation of Bitcoin was to create a system where the identity of the creator is a mere historical footnote. We can probably go further, and state that while doing so, Satoshi quite counter-intuitively took steps to avoid even creating a pseudoanonymous identity." - Peter Todd, https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015...

And of course, the most important sentence is from Satoshi's message itself:

"Bitcoin was designed to be protected from the influence of charismatic leaders, even if their name is Gavin Andresen, Barack Obama, or Satoshi Nakamoto."

So whether it's Satoshi or not, it doesn't matter; Bitcoin was intended to transcend even Satoshi's own influence.