“While it might sound counterintuitive to keep readers on their toes, the strategy has been proven by ProductHunt as well as other companies, like Timehop and iDoneThis.”
Use this unconventional, but proven, approach if you want to promote interest in your ongoing emails. Try to strike a balance. You want readers to know what to expect from you, but you want to excite by offering newness that your subscribers will appreciate and value.