Translation from German to English
What? Pay for T-Online not to mess with sender addresses? They're completely crazy.
Fortunately, I'm my own provider in more ways than one and don't need this crappy relay, but instead use a tunnel to my own static IP with full connectivity. But anyone who can't do such tricks but still wants to use their own domain (and uses mail forwarding for that, for example), will now be nicely ripped off by T-Online.