One of the issues mentioned is that bulk mail and spam are not necessarily the same thing. However, bulk mail much less use for e2e than directed mail. Persona

One of the issues mentioned is that bulk mail and spam are not necessarily the same thing. However, bulk mail much less use for e2e than directed mail. Personalized bulk mail (e.g. bulk mail with a small personalized offer) is an issue here. For that, partial encryption seems like a nice solution. As the template remains plaintext, reputation can include the template. As such, you could levy a lower 'tax' on such email as opposed to fully confidential email.