How to include a Bootstrap glyphicon in an email with Laravel

I have an app that sends out a notification email. I would like to include a Bootstrap glyphicon in the email, but what I'm doing just results in a blank space where the link should be (I'm using the glyphicon for a link button).

Here is the code being used in my email template:

<a href="" style="margin-left: 2px; color: #EC9720;" title="Submit a Correction"><span class="glyphicon glyphicon-upload"></span></a>

I have also included the CDN for the Bootstrap library:

<script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/js/bootstrap.min.js"></script>

That doesn't seem like I'm giving you much in the way of code, but aside from the standard Mail::send() function and html part of my email template, there's nothing else to it.

via Chebli Mohamed