Ok, i know. Now i use bussines calendar and OpenTasks with davdroid.
Syncing a calendar with Exchange Web Services (EWS)
Newer Exchange versions communicate via the “Excahneg Web Services” protocol, a SOAP API which is acutally documented.
Currently, there is no open-source possibility to sync such a calendar to your phone. It would be awesome, if davdroid could support it.
Thanks for your suggestion. This would be a new project, because DAVdroid (as its name indicates) is focused on CalDAV/CardDAV and not intended to be a multi-protocol sync adapter.
The ical4android and vcard4android libraries (which were primarily created for DAVdroid) could probably be reused.