There's no account setting for this that I'm aware of. (And I just looked again, and didn't see one.) This would be a lovely feature!
For this reason, I prefer in-app and Slack DM notifications. They still come through individually, but they're much more easily dismissed* at a glance than email — psychologically, at least. Gmail shortcuts make it simple to dismiss all notifications, but that still takes about a dozen keystrokes and much more cognitive load than a couple of mouse clicks to clear a Slack unread notification. And I like the way the iOS Beeminder app badge keeps an up-to-date count of the day's pending Beemergencies.
— Anyway, email notifications boo!