A user has requested that <font> tags be added to the list of HTML elements that are not stripped out of the WYSIWYG editor when clicking save. They had part of their email body that they needed to wrap in <font face=""></font> in order to make their emails work in Outlook 2007/2013. Doing so in the email's HTML template is not ideal, as it would apply to the entire email body.
Update 12/19/17 - updates to the WYSIWYG are planned for December 2017. Please follow Better WYSIWYG editor and media upload/management for WYSIWYG change notes.
Font tags are no longer supported by the HTML5 standards. It is recommended to use CSS instead, such as an inline-styled <span> tag.