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

UX in Email Design

http://www.webdesignerdepot.com/2016/01/ux-in-email-design/

10 Awesome Hacks For Emails That Convert

https://designschool.canva.com/blog/newsletter-design/

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

Email Design Workflow

http://www.leemunroe.com/email-design-workflow/