@z428 look, if you want all the contacts just to be able to answer each other or see each others answers, you have to tell every server and other user who is allowed and should see the answer of every other participant.
So you have to technically group and share this "virtual group with all participants" to everybody else in the group. Otherwise nobody knows who to send replies, except to you.
Even this might be possible in other protocols, you have to trust every other involved node, that it respects your intention to privacy and keep the closed list that you set initially.
@z428 yes everybody has to be in that forum or group. That what you are trying is something like a "private public post Chimera".
You can do that if you have every other node in the fediverse under your personal control. Since this might a little bit difficult and guides to some serious discussion potential besides the node owners (and users) you should maybe rethink the reasons why you want to do that.
The more polite way of "grouping" people is to ask/invite them to join a group/forum by their own free will. There might be a chance that some of the people are not happy to be put in a half-public "Opt Out" selection by some strangers. :smiley187:
@z428 this feature is called "a forum" or the upcoming "groups"