10 epic email marketing predictions for 2016

https://www.campaignmonitor.com/resources/guides/email-marketing-predictions-2016/

The psychology of colors in email marketing

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

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

How to grow your business with newsletters

http://blog.astonishemail.com/blog/2014/12/1/using-email-newsletters-to-help-your-business-grow-and-prosper

Is there an ideal subject line length?

http://www.marketingsherpa.com/article/chart/subject-line-length-success