If you are encountering issues changing fonts in the message editor, there may be a problem with the HTML code of your message. Though rare, a possible cause for this might be poorly written HTML code or content copied and pasted from another program such as Microsoft Word. In the case of Microsoft Word, there are office-specific HTML tags that are generated when the content from a Word Document is converted to HTML. In some cases, fonts/sizes may be declared multiple times in the HTML code and will need to be cleaned up.
When pasting content from Word, click on the icon that looks like a clipboard with a Microsoft Word symbol on it. This will attempt to convert content from MS Word into SimplyCast. This will help minimize the amount of re-formatting that you will have to do after the content has been loaded into the system.