Comment by ozgurds

This mainly depends on what is the general lifecycle of those emails and how does it interacted with users. If you are sure that you never spamed any users before , then we should think about how the google spam labeling works. For example if you send a bulk email for a mailbox of many emails and those emails were labeled as spam then it may cause this situation maybe. Is there a way to get life cycle of your email box from google maybe ?