Suggestion - stop making your email addresses for book offers look like spam.
I'm surprised that Sitepoint - of all places - is using email subject lines like this:
50% SAVING + FREE PHP poster with Kevin Yank's New 'PHP & MySQL' Book
and "from" email addresses like this:
Our GWAVA5 company spam filter (which is where all of these go even if I try to set them as "ham") rates this as "Spam threshold 4" with a score of "0.95". I don't see anything higher than Threshold 5 and a Score of 1.0 for actual spam. It's not suprising given these well-known spam triggers: capital letters - "50% SAVING" - "FREE" and the fact that "cmail5.com" does not match the domain sitepoint.com.