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<p>This is presumably done by embedding URL images (which are not necessarily visible-to-human images) in HTML email, so if you open the email in a plain text email reader or one which does not open embedded URLs (typically for security purposes), the opening of the email will not be noticed.</p>
<p>So this means, after reading the email from the college in an email reader that does not open embedded URLs, do so with opening of embedded URLs once you have verified that it is legitimate, so that the “has read the email” counter gets triggered.</p>
<p>Of course, if there is a link to the college’s web site that you are supposed to explicitly click to, it would be a good idea to go there and browse, since that may be a more explicit way of tracking interest from the email.</p>