DAVx⁵ has been successfully tested with MDaemon.

MDaemon is an email server that offers flexible email management, security and collaboration features for on-premises, virtual, or hosted server deployments.

DAVx⁵ settings

Base URL: https://yourserver.tld (for instance:

Contact group method: groups are "per-contact categories"

User name and password: Use your email address and password to log in.