If you get this in your autoresponder service this could be the reason. In order to track the number of clicks you get they put a little image in your message that is hidden to you but tracks the number of opens and clicks that you get.
That's why even after removing words like "FREE" etc you still get a high spam rate. Also, if you have some pictures in your message make your content longer so that you content to picture ratio equals more content to less images. This will help get your emails delivered as well.
Other tips include making sure that you have your address at the bottom of your email and unsubscription link etc. Some Autoresponder companies automatically include this but others don't.
that's all for now.
p.s. If you have other tips to help improve message deliverability do share