It is especially difficult to stop others from just blackholing your email. This serverfault question helps to illustrate the problem http://serverfault.com/q

It is especially difficult to stop others from just blackholing your email. This serverfault question helps to illustrate the problem http://serverfault.com/questions/434703/why-does-hotmail-still-reject-my-emails http://serverfault.com/questions/434703/why-does-hotmail-sti... The problem? Not enough traffic causing a low sender score. Hotmail isn't the only one; large and small ISPs across the world do it.