사이드바의 "메시지"에서 받은편지함 제거

[MarcP]

So to answer this for reference:

The inbox needs to be empty, including the archive. Then wait max. 12 hrs or:

Messaging: Group inboxes and archives show even after all messages deleted

Note you can manually kick off the weekly task by going to /sidekiq/scheduler searching for Weekly and triggering that.