You may prefix any file name with anything you like to help you identify the files more easily in your IDE. The only requirement is that the filename contains html., text., style., and subject. respectively. Use an email service or tool that will automatically inline your CSS for you. Web browsers display interactive, dynamic content, and they update often. There are a number of options you can use – consult the Premailer documentation for more details. Not all email clients support these elements, so we recommend that you thoroughly preview and test your campaigns before you send to your entire list.