Earlier quoted context omitted.
> You're supposed to stop sending emails to someone who's not interacting with them The only way that this justification makes sense to me is if you mail people that didn't explicitly subscribe to your newsletter in the first place. If that's the case, I think that the problem lies elsewhere. An email is meant to be read, that's it. Any other interaction a user will have with it that is still under your concern is if…
That may be how you want it to be, but it doesn't reflect reality. If you consistently have extremely low open rates (e.g. you send to a lot of people who aren't opening) your risk of being marked as spam increases. The only way to avoid this is to periodically cull your list of people who haven't opened in some amount of time.
I consume most of my email in plain text format. Like me there are others. Your solution is not working for us.