Sharepoint - Connect a List (Calendar, Task) with Outlook Results in an Outlook Error 0x8000FFFF

I found the problem.

The server was using a self-signed certificate on a local domain (company.local) When connecting over the internet to that machine the browser (and outlook) trys to verify if the certificate was revoked. This fails because the domain of the certificate is invalid for use of the internet. IE handles this correctly but Outlook doesn't (same for other office applications)

Quick solution: Disable certificate checking in your internet settings (Internet settings -> advanced -> Check if certificate was revoked ) BUT: this is a security risk, since it is a global setting, e.g. your OnlineBank transactions may not be secure anymore!

Good solution: fix the certificate and/or buy a 'real' one.

What authentication do you have?

Also this may be an issue with using high port numbers over the internet. Can you connect in the server when in the office?

This error is reported if you are not connected to the VPN. Where you able to access SharePoint, when this error was occuring?