On the other hand, GMX (and web.de) is a notoriously bad influence on email communication and will randomly block mailservers if they feel like it while flooding all of their own users with spam. The world would be a better place without 1&1 / united internet.

https://slate.com/news-and-politics/2013/06/prism-j-edgar-hoover-would-have-loved-the-nsas-surveillance-program-topic-government-surveillance.html

This is a decent read concerning the effectiveness of the systems designed to prevent abuse.