Sorry everyone for the late reply!
Kerry I haven't heard that this would be the case. If you tell me your forum URL, I will look into it when I have spare time
tom23 Yolo thanks for letting me know. I have checked the mail queue, and it seems that T-online refuses mail from FreeFlarum due to "bad reputation". Because other mail providers are fine with FreeFlarum, I have mailed T-online and asked them to clarify - I'll let you know
orschiro the language selection is unused/broken for quite some time now... Perhaps I could hide that section for the time being. Anyways, thank you for the info
orschiro not sure what went wrong there, but I've re-linked your domain, and it seems to work now