The 6 Best Practices for Responsive HTML Email Design https://mailbakery.com/blog/the-6-best-practices-for-responsive-html-email-design/
Email Development Best Practices https://www.emailonacid.com/blog/article/email-development/email-development-best-practices
9 Tricks to Design The Perfect HTML Newsletter http://www.hongkiat.com/blog/design-perfect-newsletter/
The Ultimate Guide to Preview Text Support https://litmus.com/blog/the-ultimate-guide-to-preview-text-support