Possible next step after [#5384].
Create moderation mechanism for spam. Some thoughts:
- Moderators need to be able to review stuff that the filter has marked as spam, as well as flag stuff as spam that the filter may have missed.
- In either case, post to the spam service's "submit-ham" or "submit-spam" endpoint if available.
- Email notification to moderators when something is flagged as spam by the filter?