Settings seems to be in /class/xoopseditor/tinymce/tinymce/jscripts/tiny_mce/themes/advanced/editor_template.js (search for andale). (Don't know why your list is not taken into account.)
For editing purposes it is enough. If the font is installed on your PC, you will see the desired result. For other users the browser (IE, FireFox, ...) will fallback to an existing font.
Probably you are hitting limits in memory use, execution time or processing power on your server. You are in the mass mailing category and this requires dedicated solutions for software and server.