We build every night our projects for testing issues. Also the system should provide on the same way the latest development state to all developers.
When a quick fix rises or extra test runs are manually triggered, it would be nice to disable email notification because the user triggering this build will observe or check it by browser. In general these actions take place during the day, so a rule like: "send email on error only for builds between 21:00 - 06:00" would be very nice.