What a interesting I found for email marketing is to use less known autoresponder services, because in my experience they tend to have better email sending rates.
For example I am using a Autoresponder from my country and it's working insanely good, most of my emails are going straight to the inbox (not even to promotion section if my leads use gmail).
Im not sure if you can see the image here, but basically ive sent 3000 emails and ive got almost 65% open rate which is insanely good and 24% click through rate, ofcourse you need to know who are you marketing.