Fractal: HTML-CSS Validation For E-mails
E-mail code validation is a painful job considering many e-mail clients/applications have a low-level HTML-CSS rendering support and many others have their own standards. Actually, it is worse than designing for the browser.
Fractal is a free-to-use web application for validating HTML-CSS code across 24 most-popular e-mail clients.
It simply works by pasting the code to the application and finding out if each line is validated, if not, why and in which e-mail clients.
Best of all, Fractal doesn't come with only the bad news but also suggests fixes.
P.S. Besides the desktop and web-based e-mail applications, it also checks the code for the mobile as well.