An umlaut domain is an internationalized domain name (IDN) used in the German-speaking world. These are domain names that include special characters (ä, ö, ü, etc.). For example, you can register www.staedtefluege.tld in addition to www.städteflüge.tld. These domain names have been available since March 1, 2004.
On the server side, this domain is converted into ASCII characters. For example, the domain www.städteflüge.tld is stored as www.xn--stdteflge-w2a3y.tld and displayed with umlauts in the various browsers and email clients.
We recommend using IDN domains (umlaut domains) only as a complement to your existing domain names because they are not yet supported by all email clients and web browsers.