@Stephen thank you! I did have staged users enabled, but indeed the email I used for testing already had an account, and did not have access to the group where posts submitted by email were getting assigned.
Can you clarify what those “group inboxes” are and how I can look into this? The above is exactly what I need to accomplish. I want anyone (registered or unregistered email) to be able to send email to a configured address, which would trigger a new post to a restricted access category, and after that it would be triaged by someone who has access to that category.
Basically, I need to have threads that are accessible by the submitter and a defined group of moderators, but not accessible by other users who post by sending to the same discourse email address.