Outlook plugin for macOS - cannot login

Outlook plugin for macOS - cannot login

I just downloaded the Outlook plugin for macOS and installed it as described.
When I try to login to my CRM-Account I always get the message "Connection failure - Please check your internet settings", but I am definitely connected to the internet.
Additionally I looked into the log files and found two interesting things:

1. Zoho CRM Plug-in for Microsoft Outlook _CFNetworkIsConnectedToInternet returning 1, flagsValid: 1, flags: 0x2
--> so I am connected ;-)
2. Zoho CRM Plug-in for Microsoft Outlook NSURLConnection finished with error - code -1003
--> that apparently means, that the host cannot be found

Thanks in advance for any ideas how to solve this problem,
Carsten