Multi-Account Harassment Countermeasure Feature

A member of my server has reported that a friend of theirs is being harassed by a 3rd party, who is making new discord accounts and joining my server.The harassment has been reported by that second-degree friend, this is a request for server features that would help mitigate such issues.

My server has an atrium system, where new joins can only enter the wider community by being whitelisted after passing a checklist. Because of how discord allows members sharing a server to chat with each other unrestricted, despite not passing border control, this person is able to harass merely by joining.

As such, I would like to request one of three possible options to mitigate this.

1: A permission. Server administration can set a permission on roles. Users would need to have a role with that permission to message (and be messaged by, for symmetry) someone on that server (who also has that perm). By default, this would be enabled on @everyone. Users could also have an override in their settings that allows the check for the other party to be bypassed, so long as either party has that permission, or both parties have this setting set. This would be part of the 'allow direct messages from server members' option. This is the one my heart is most set on, since it would allow option 2 to be simulated by server admins through permissions, with the most versatility. Probably with another permission for 'unilateral' chatting, for staff to also be able to dm people, and receive dms.

2: A tighter filter. Instead of sharing a server, both parties would need be able to see and speak in at least one shared channel (with view-channel-history counting as a sight block) before the 'sharing server' thing comes into effect, allowing them to DM each other. This is the most viable, since it would enhance security passively, without anyone needing to make a change. A possible tweak would also be to allow server admins to disable this feature for certain channels.

3: A combination of the previous two. I'm really just including this to satisfy the rule of three, but it's entirely unfeasible to do.