“Most common mistakes we see are improper offer communication or not prominently displaying the offer. Everyone is expecting sales, and everyone is getting a ton of emails; so in this period, it is best to go with the offer directly in the Subject Line, followed by any additional offer (free shipping, extended warranty, 30-day money-back guarantee, etc.), or emphasizing the urgency in the Preheader. If you go without it in the opening line or if you’re too subtle in the Preheader, you risk the chance of a subscriber not seeing it and converting, no matter how good the offer is.