Hi @smguenther,
just to confirm, you are talking about the global addressbook in Kopano (so the ldap tree) and not a users contact folder? (especially the second part leans strongly toward ldap, just wanted to be sure anyways).
I think on UCS csv import is only part of UCS@School, but should be easily scriptable with udm even if you are not running it. I managed to find the following example, which only needs to be extended for the Kopano relevant attributes: Csv Datei integrieren