He need not pass it off as his own. He could clearly indicate that the e-mails were created by others, that identifying information has been changed, and give attribution where appropriate or necessary. But scrubbing the identifying information, trademarks, etc would at least remove one layer of potential problems, I think. Certainly the best thing to do is take the e-mails he wants to use to intellectual property lawyer for review to see how he might be able to make this work without facing legal or other unwanted problems from the creators or senders of the e-mails.