The email chain also shows that he knew that the the Russian government was the source, although it appears they might not have been.  Also, it appears that the email is part of a continuing conversation he had either in person or some other means prior to this email.

Here is page 4 (which did not post due to space constraints). pic.twitter.com/z1Xi4nr2gq

— Donald Trump Jr. (@DonaldJTrumpJr) July 11, 2017

It is appreciated that Trump Jr. has decided to get ahead of this story by posting the email chain to stop speculation. This is the type of activity that the Trump administration should have done from day one but instead, they have decided to play the same type of game that Hillary Clinton played in trying to delay and deny.