Thirteen Pro Tips for Email Design

https://medium.com/mailchimp-for-agencies/thirteen-pro-tips-for-email-design-6612d9a3769

The psychology of colors in email marketing

https://www.mailjet.com/blog/psychology-of-colors-in-email-marketing/

Email Preheaders: Ignore them at your peril

http://www.inboxmarketer.com/blog/~1389-Preheaders-Ignore-them-at-your-peril

A/B testing your email design – 10 tips not to overlook

http://www.adestra.com/ab-testing-your-email-design-10-tips-not-to-overlook/

25 Email Design Resources to Help You Create Stunning Emails

http://www.pinpointe.com/blog/email-design-resources

The Power of Split Testing in Email Marketing

http://blog.astonishemail.com/blog/2014/12/1/the-power-of-split-testing-in-email-marketing