8 sites to get free images for your next email design

https://www.campaignmonitor.com/blog/email-marketing/2014/07/free-images-email-marketing-campaigns/

10 Awesome Hacks For Emails That Convert

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

Responsive design options for navigation in emails

https://www.displayblock.com/2015/08/19/responsive-design-options-for-navigation-in-emails/

Design Teardown: Reimagining Email

A Guide to Bulletproof Buttons in Email Design

https://litmus.com/blog/a-guide-to-bulletproof-buttons-in-email-design

Six Great Responsive Email Designs

http://blog.lyris.com/email-inspiration-six-great-responsive-email-designs/