Many people noticed and I could hardly keep up with answering all the emails. My site was offline for almost a week. Unfortunately, the previous host was not very competent when it came to troubleshooting. There were/are routing problems in the data center. But I took advantage of the downtime and moved this site to another hoster. So the site is finally back online.
Unfortunately, this also took some time, because the former hoster let some time pass until he transmitted the Auth. Codes has transmitted. All in all, I'm glad to have the site with a new provider, as the former hoster caused me quite a few headaches.
While I'm writing this article, I get an email from the old hoster: "The problems have been fixed" :-D
Thank you very much for the e-mail, apparently nobody has noticed that it is no longer their problems :-)