From the article intro: "SPAM filters can be triggered for a variety of reasons, causing your email to skip recipients' inboxes and land straight in their SPAM box.
One of easiest ways to avoid SPAM filters is by carefully choosing the words you use in your email's subject line.
Trigger words are known to cause problems and increase the chances of your email getting caught in a SPAM trap.
By avoiding these words in your email subject lines, you can dramatically increase your chances of getting beyond SPAM filters.
Next time you sit down to write an email subject line, consult this exhaustive list."
The full spam trigger word list: http://blog.hubspot.com/blog/tabid/6307/bid/30684/The-Ultimate-List-of-Email-SPAM-Trigger-Words.aspx