Maybe you’ve also had problems with new members (ab-) using the reply-by-email feature. I feel that if you force users to first get a grip of your Discourse instance by using it via web, things run more smoothly. As soon as they reach TL 1 or 2, it’s pretty safe to include the reply-by-email feature (which I personally really like a great deal!).
In order to have a setting like so:
…I wrote this tiny little plugin:
which does the trick. I really see this more of a “ironing out tiny wrinkles in a great product”. But maybe you have the same problem in your community, so here’s a potential solution.