Email marketing is a blood sport. In the last 20 years, the only thing that’s changed with email is that good email senders continue to get punished more and more by email service providers. While ISPs and ESPs could totally coordinate if they wanted to, they simply don’t. The result is that there’s an adversarial relationship between the two. Internet Service Providers (ISPs) block Email Service Providers (ESPs)… and then ESPs are forced to block clients.