Directus 9, do i set permissions on Files?

[mfmaut]

first of all i am so far totally happy with the new directus 9, great work :)

I have an App with private messages , the messages are stored in a directus collections, each item has multiple Attachments (files).
How can i restrict access to these files for other users, that are not in the Conversation?

Do i have to set up a usergroup for each conversation?

And another question, how can i set the "mine" permission on files?

Thanks

[mfmaut]

I think the issues panel is the wrong place for questions, i found the discussion panel