I also implemented a vaguely Hey-inspired system in Fastmail a year ago and it's been good. One tweak that's really helped me: when I filter things to "The Fee

I also implemented a vaguely Hey-inspired system in Fastmail a year ago and it's been good. One tweak that's really helped me: when I filter things to "The Feed", I also use the filter to snooze them until 6pm, so I only get mailing list emails once at a day.