To use domain names with umlauts or accents (known as IDN domains = Internationalized Domain Names) as URLs or email addresses, several technical requirements must be met:
An IDN-compatible registrar (e.g. Webland.ch)
An IDN-compatible provider (e.g. Webland.ch)
IDN-supporting software on the end user’s device (e.g. browser or email program)
All three of these conditions must be met.
If even one of them is missing, your website or mail server may not be reachable or function correctly.
To successfully use email accounts with umlauts, both your own system and the email software of your recipients (e.g. Outlook, Thunderbird, etc.) must support IDN domain names.