I was very disappointed that "Maximum percentage of failed or deferred messages a domain may send per hour" is a percentage. I was hoping to limit ALL accounts to a figure of 10. I don't use "Max hourly emails per domain" because i have a lot of clients with mailing lists. So that means i can't limit failed or deferred messages either..... unhappy.
Would have been a great spam control option but it turns out to be useless.