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

• 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/my.name@outlook.com/calendar/TestKalender/ and it works. I may add schedules or remove them in Evolution.

I will be happy to provide more information.

Start by reviewing config.txt and debug.txt, then reproduce the server-to-server sync described in the advanced collection configuration documentation. Run vdirsyncer -vdebug against the Outlook/DavMail and Mailbox.org CalDAV endpoints, using the working Evolution Mail URL as a comparison. Done means identifying and fixing the sync failure and confirming that calendar changes propagate between both servers.