I recently tried to post a reply by email, and got an error bounce. The subject of the email was “[Discuss] Email issue – Unknown To: Address” and it listed a number of possible reasons my email couldn’t be processed. However, I’m pretty sure it missed the real reason - I sent it from the wrong email address. Instead of sending it from the address which is registered as my user on the site, I sent it as my usual, personal email. Perhaps this can be added as another possible reason in the message, and maybe even detected by the system.