Can I insert my own custom font into the editor?

Fonts other than the standard web-safe fonts, such as: Arial, Times New Roman, Verdana, Georgia, Tahoma, Lucida, Lucida Grande, Trebuchet MS, and Courier, will not display in the vast majority of email clients.

If you need to use a special “extra” font, the only reliable method is to create an image and add the text with your desired font onto that image using a program like Photoshop.