we use Slack a lot. It ensures deliverability and helps us collaborate, but isn't really taking the place of email. We find it indispensable though...and yet we still use email.

I've been aggressively unsubscribing which is helpful. Lots lower volume this way.

Also I use Sanebox. That creates a high priority email experience, putting all the rest in a separate folder for later.

Together these seem to make email quite manageable for me.