For my part, I'm doing this quite recently.
I go through a provider to create and transform it into html. (more for lack of time and to have a pro newsletter). Design is very important
The problem is that for the moment, I have a base optin but not targeted, Indeed a promo on football for a guy who is rugby or tennis he does not care. Suddenly on the new commercial site to come with ClicShopping, I will sectorize my bases by sport.
I used Mailkitchen, not bad but my open rate has only decreased mailing in mailing, but I will also test mailjet for the future with a dedicated ip.
I really miss practice at this level.
I did some tests on the time of sending, the subject or the sender, but I have not enough mailing sent to really know.
I did not do A / B test.