Steps to reproduce:
- Use a forum in mailing list mode.
- Receive a forum message from someone you want to stay in contact with.
- Add the sender to your address book, because you think this works like an old-school mailing list.
- Send a private message to that entry in your address book.
Oops. Your private message went to the whole community.
I’ve witnessed this in a community that uses a competing forum application (I won’t name and shame here), but it affects Discourse as well.
When sending to the address in the From header, the message should either bounce, or go to the sender as a PM. Maybe the forum administrator should be able to choose the behavior.