> Companies and online media outlets, such as newspapers, magazines and journals, wishing to operate within any of these countries are obliged to make this information easily available to users. This requirement also applies to legal entities registered outside of the German-speaking realm that compete on the respective German, Austrian, or Swiss markets.
[0] - http://www.it-recht-kanzlei.de/nicht-eu-ausland-impressumspf...
[1] - https://www.1and1.com/digitalguide/websites/digital-law/a-ca...
EDIT: added a source in English
All WHOIS protection services I’ve seen until now either ignore fax, phone and letter, or just respond with "this method of contact is ignored, please use the email"
Typical example: https://www.rockit-internet.de/impressum/