Cover Story: 50 Best Tips of 2009

9. Use promotions in your transactional emails.
About 80 percent of commercial email isn’t opened. But transactional emails (e.g., “Your product was shipped today”) are opened and read at about double the rate of promo emails. While customers are reading about their transactions, promote a related product below the fold.
Arthur Middleton Hughes, e-Dialog
“3 Tactics for Email: Promote, Personalize and Be Relevant,” July 21, The ROI Report