When adding an icon such as <i class="fa-light fa-envelope"></i> (the format which FontAwesome recommends), the icon's HTML disappears upon saving. We figured this was maybe due to the type of tag used (the i tag), so we tried using a div instead (<div class="fa-light fa-envelope"></div>). This div is not stripped from the HTML but the icon is not rendered.

Please allow inserting icons in the Editor content.