So that the domain name can be used with umlauts and accents (IDN = Internationalized Domain Names) in the internet as URL's and e-mails, various technical pre-requisites must be fulfilled:
IDN supporting registrar (e.g. Webland.ch)
IDN supporting provider (e.g. Webland.ch)
IDN supporting software with the end-user (browser, e-mail program)
It is absolutely necessary that all three points be fulfilled since otherwise your website and/or your mail server is not reachable. For anyone to call up your homepage with umlauts, that person’s local software (e-mail program) must support domain names with umlauts.