Six tips to use symbols in subject lines http://www.emailmonks.com/blog/email-marketing/6-godly-tips-to-use-symbols-in-subject-line/
Responsive: Fluid content alignment http://blog.newzapp.co.uk/2014/10/essential-responsive-email-code-fluid.html
Image Rollovers for Mobile and Non-Mobile Email http://freshinbox.com/blog/image-rollovers-for-mobile-and-non-mobile-email/