May 1st = Postmark deadline?

<p>Postmark deadline or received by deadline?</p>

<p>According to the Caltech website <a href="http://www.admissions.caltech.edu/applying/deadlines%5B/url%5D"&gt;http://www.admissions.caltech.edu/applying/deadlines&lt;/a> May 1st is the postmark deadline.</p>