Thanks for the reply.

I Agree that marketing email are super obnoxious. In the very few instances that we send (e.g. black Friday), we include an unsubscribe link :)

Yes, we are informing our customers to flag us as not spam. However, our domain reputation is 100% (google's postmaster) according to Google's support, this doesn't seem to be the case.

We will continue informing our customers and helping them set filters so they can receive our emails (eg. forgot password and other important emails). But everything on Google's side is showing as OK and we are still left without an answer.