DAVx⁵ has been successfully tested with Posteo.

posteo is an independent German mail provider, focused on renewability, security, privacy and easy usage.

DAVx⁵ settings

Choose "Login with email address" and enter your Posteo email address and password.

If this doesn't work, you can try:

Base URL:
User name: your posteo email address
Password: your posteo password

Contact group method: vCard contact groups are not supported. Choose the method used by your other clients or "per-contact categories" to minimize potential problems.

Known problems

There are known server problems with contact photos, recurring events and reminders. We have already reported those problems to Posteo.