Starting today, well show a brief explanation at the top of each of your spam messages. Simply look at any message in your spam folder and now you can find out why it was put there. And if you’re interested in learning more, check out our new series of spam articles in the Gmail help center. We hope that this is not only interesting, but also helps you learn about scams and other harmful messages that Gmail filters out. Whether you prefer to leave spam folder untouched or do some educational digging, the information will be there for you.”]
Source: https://gmail.googleblog.com/2012/03/learn-why-message-ended-up-in-your-spam.html