If the content of your email or frequency of emails is not inline with the expectation of subscribers when they subscribed, some will report the emails as spam regardless of the steps you documented.
Sure, we have been doing this for several years so we are aware of these pitfalls. The issue is the way Google has been handling this case. There is no process, no communication. They have made extreme threats, with nothing to back it up, no way to respond.
This a thousand times. We also go to greath lengths to ensure there's no spam coming from our servers and then we get a notification and it's for a legitimate email that someone reported as spam for whatever reasons. It's frustrating.