One suggestion -> create another group, an extra group, and put all the users / groups you want to have access in that group but the one that should be excluded.
I don’t have the “external” group on my samba server
-> so I had to create it and the samba will populate it with users present on group creation time
-> future user will not be added in “external” group
This is the reason why I am trying to do it with a group to exlude.
If owncloud can’t do it, I will use your solution and trying to create an update script for my external group
I don’t realy understand why it is possible to select people because they are of a group and not the reverse thing. (people that are not of a group - like a !groupA in programmation language)