<p>So, I will have my online app sent before Jan 1. However, I need to mail other app materials, but I was wondering if the deadline was postmarked as its website didn't specify at all. </p>
<p>Same question about Dartmouth too if there are any answers.</p>
<p>Officially, it's a "receive by" deadline. However, if you're planning to mail an integral part of your app (ie, an essay), Duke will notify you that they lack that piece of your file and then give you a few days to submit it with no penalty.</p>
<p>However, it's always better to be safe than sorry--submit early!</p>