See external feedback at Ticket#2017102021000481 Having UCS as domain controller with Samba 4 and Kopano installed, the uid attribute is not set at a newly created user, when the Kopano user template has been used. Furthermore, no Kopano mailbox is created. The flag gets set, when the Kopano user role is deactivated and re-activated again.
Never mind. Fixed with Bug #45066. Was in my backlog.
*** This bug has been marked as a duplicate of bug 45066 ***