Conpherence has two blunt settings for email. Send it all or none. We should add some granularity and select sensible defaults. In the general case, we don't want to auto-send email, but cases like mentions, topic changes, getting added or removed to a Room, the user might want a email. The main reasoning here is Conpherence itself has no push notification ability, so email for now acts as a proxy.
**Send me emails:**
- [ ] When I'm mentioned
- [ ] When I'm added or removed
- [ ] When the topic changes
- [ ] When a new message appears
Thoughts?