Domains with mutated vowels have first to be converted into the technical realisation of your web browser and email programmes (so-called puny-code).
kernöl.at is first converted into xn--kernl-mua.at).
To do this, some programmes need an additional extension programme (Plugin). In topical browsers (IE from 7.0, Mozilla, Safari from 2.0) it has already become a standard installation.
Please find this extension for Internet Explorer and Microsoft Outlook or Outlook Express under:
http://idnnow.com/index.jsp?lang=de