When you try to sign in the first time to Microsoft Skype for Business in the German version of Microsoft Office 365, you receive the following error message:
We can't verify if the server should be trusted. Do you want to continue signing in?
To work around this issue on your Windows client computer, use the workarounds that are listed in the following Microsoft Knowledge Base article:
Artikelnummer: 4012361 – Letzte Überarbeitung: 06.02.2017 – Revision: 5