HubSpot Blog
https://blog.hubspot.com/

Really Good Emails
https://reallygoodemails.com/

The Email Marketing Blog
https://www.emailcenteruk.com/blog/

Marketing Forward
http://www.experian.com/blogs/marketing-forward/tag/email-marketing/

MarketingProfs
https://www.marketingprofs.com/marketing/library/17/email-marketing

Pinpointe
http://www.pinpointe.com/blog/

FreshInbox
http://freshinbox.com/blog/

Pure360
https://www.pure360.com/blog/

Drip
https://www.drip.com/blog/

EDMDesigner
https://blog.edmdesigner.com/