Any e-mail client with rules can do that and much, much, much, much more, though. Slack only offers three primitive options for notification filtering, and they can only be applied at two levels.
That's because you're using Slack wrong. You push notifications for a particular topic or event into a Slack channel. You then set notification settings on each of those channels.
Slack isn't the filter, it's the data store and UI.
If you want different types of notifications.. I'd just notify on the urgent stuff and then manually view particular topics at your leisure.
