This is something that took me more than 5 hours of testing, installing, reinstalling email related modules applying patches, changing from stable to dev versions and trillions of watchdog log messages. No matter what, nothing would fix my simple problem: HTML E-Mails are being sent out as plaintext when i am using the simplenews module.
So the solution is pretty simple basic but as always it was "hidden" in a simple radio box admin sub tab/fielgroup form page.
Go here: admin/config/services/simplenews/categories/[your-simplenews-taxonomy-term-id]/edit (for d7)
or go here : admin/config/services/simplenews and click the "edit newsletter category" link.
At "Email Settings" simply change Email format to HTML.
Thank you drupal community for once more, you rock!
https://www.drupal.org/node/1193744
simplenews
mimemail
htmlmail
mailsystem
