In email design, “responsive” is not just mandatory, it is fundamental. Because the mobile open is almost bounced to top. Here I am writing email design tutorial twice or thrice in week. It is plain, simple and to-the-point. Most of the email clients and builders are module (or section) based, so the tutorial is designed based on it.
There is no standard in email coding. It is still table based. We have to write code for various email clients like modern mobile app email client to classic old Outlook 2000.
Here is basic structure of email code. Click to enlarge the image. This code style may change in future.