I'm asking how does Google differentiate between a transactional and a non transactional email?
They also say in their guidelines
> *Marketing messages and subscribed messages* must support one-click unsubscribe, and include a clearly visible unsubscribe link in the message body.
So how is Google determining what is a Marketing/Subscribed message? If they're not, then am I required to tack on this header to ALL emails regardless of type or risk getting binned?