No, the server is "open" since the relay is open, it makes no difference. The only protected resource is nip05 names and there's no way to manually assign them. The user has to request one for you to approve.
nostr:npub1gujeqakgt7fyp6zjggxhyy7ft623qtcaay5lkc8n8gkry4cvnrzqd3f67z
Is it already possible to send invites in a way?
No, the server is "open" since the relay is open, it makes no difference. The only protected resource is nip05 names and there's no way to manually assign them. The user has to request one for you to approve.
Ok clear. So how does that request process look like?