I’ve had some troubles finding good blogs about email marketing and EDMs generally, here are 3 that I have found to be good.

http://blog.sendsmith.com/

http://stackoverflow.com/questions/30614808/responsive-edm-issue

http://blog.hubspot.com/blog/tabid/6307/bid/32854/10-Simply-Awesome-Examples-of-Email-Marketing.aspx

When comparing the 3 email marketing blogs above, arguably the best is the the SendSmith Blog