Choose "Login with email address" and enter your mailbox.org email address and password.
If you use your own domain with mailbox.org, use the "Login with Base URL" option:
Username: your email address
Password: your password
Contact group method: There is no server-side CardDAV contact group support. Choose "per-contact categories" as contact group method to minimize problems.
There are some known limitations:
- Contacts: Not all email addresses and phone numbers are always stored and/or shown in the Web interface. For more information, see AppSuite:VCardMapping.
- Calendars: Events which are more than one year in the future seem to be not sent over CalDAV, so they can't be synchronized.