server-to-server sync fails with Outlook (DavMail) and Mailbox.org (CalDAV)

[ErikSteiner]

• Your vdirsyncer version: vdirsyncer, version 0.16.9.dev0+gb5dd092.d20200713
• If applicable, which server software (and which version) you're using
• Your Python version: Python 3.8.6
• Your operating system: Manjaro 20.2
• Your config file: see config.txt
• Use vdirsyncer -vdebug for debug output: see debug.txt

I created one calendar on Outlook and on Mailbox.org to test server-to-server sync.

The calender is called TestKalender on Outlook.com and on mailbox.org. The latter has CalDAV support. I get access to Outlook via DavMail. To test DavMail I added the calendar to Evolution Mail with the following URL: http://localhost:1080/users/[email protected]/calendar/TestKalender/ and it works. I may add schedules or remove them in Evolution.

I will be happy to provide more information.