If a Security Warning "Do you want to run this file?" appears, click "Run".
Make sure, that the ticks at "I accept the terms in the License Agreement" and "Create mail profile" are activated and press "Next".
Activate the tick at "Configure as default mail profile" and enter the following data:
Server URL: https://groupware.stepping-stone.ch/usm-json
Username: Your Groupware Username (Email-Address)
Password: Your Groupware Password (Email-Password)
Afterwards click on "Install".
In case the question "Do you want to allow the following program to install software on this computer?" appears during the installation, confirm with "Yes".