Approaching email development this way transitions more of the quality assurance (QA) process to the browser instead of the email client. It gives email designers more power, control, and confidence in developing an email that will render gracefully across all email clients.

This approach also splits email development for modern email clients and older clients in two. You can use Safari/Chrome to test and develop modern techniques for WebKit-supported clients while using Firefox for your baseline experience for older clients like Outlook.