Responsive: Fluid content alignment

http://blog.newzapp.co.uk/2014/10/essential-responsive-email-code-fluid.html

A crash course in the essentials of email design, coding and data

http://www.exacttarget.com/products/email-marketing/email-design-toolkit

Can Email Be Responsive?

http://alistapart.com/article/can-email-be-responsive

Ideas Behind Responsive Emails

https://css-tricks.com/ideas-behind-responsive-emails/

Responsive Email Design Guide

https://www.campaignmonitor.com/guides/mobile/

Six Great Responsive Email Designs

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