One of the reasons those mails get marked as spam in the first place, is because a lot of site owners use a 'From' email address that is from a different domain than the one from which the email is being sent. It's a common spam filter because that's the way most spam formatted and sent.
It would be cool if such remarks were also added to the tutorials, as comments, or P.S.s, or whatever - every bit helps and having it all in one document is very handy.