I think Gmail hides IP addresses.... I suppose it's just a coincidence that this email was sent 13 minutes after the hour and Desmogblog's first post on the subject was also 13 minutes after the hour.... Not sure of the time zones involved.
Keith Kloor gave an excerpt of the email here.
Dear Friends (15 of you):
In the interest of transparency, I think you should see these files from the Heartland Institute. Look especially at the 2012 fundraising and budget documents, the information about donors, and compare to the 2010 990 tax form. But other things might also interest or intrigue you. This is all I have. And this email account will be removed after I send.