I guess the OP's point is that if you're storing everything on a db anyway i.e. 1 row per user,per email and a sent/not sent status flag against each row - the

I guess the OP's point is that if you're storing everything on a db anyway i.e. 1 row per user,per email and a sent/not sent status flag against each row - then why do you need a messaging system? The email sending system could just poll the db for emails to be sent (by status=not sent), and then update the status after sending, as well as a timestamp for later cleanup. A more robust system is then achieved completely without messaging. Of course polling is never a great design, but I guess that's the crux of his question.