Just to clarify. Authentication is a means of discovering whether the sender really is who they say they are. But that doesn’t tell you if the sender is a good emailer or a bad one.

Goodmail is about email certification. Which is a stamp of approval for the sender. You can’t get certified without meeting pretty stringent criteria. Spammers could not get certified. (If they somehow did, Goodmail would go out of business in a flash. So it’s not going to happen.)

There are other email certification alternatives too, using different models, such as the ones offered by Return Path’s Sender Score Certified and Habeas’s Safelist.