> "responding to posts on their wall by posting on that very same wall."
That seems to be kind of natural because the conversation sticks on one place.
> "That way, the user replied to does not get a notification."
That is indeed a problem that should be fixed.
We definitely need a reply link (i actually thought there is one, but I was wrong). Idea: Fetch the reply event, transfer the userid, send an email on message submitted.