Way back nearly two decades ago, I set up an early version of ActiveSync on my Palm Treo device. I noticed there was an option in the Treo email settings to disable real time syncing between certain times (after office hours), but I was SO excited about getting and responding to real time emails on my little phone device that I thought "Who the HECK would want to stop this wonderful flow of emails". Later when I upgr…
Have all mail pre-filtered into categories with a bayesian (or similar) filter trained by the user themselves.
What this means in practice is that you have a bunch of categories for emails that are not urgent, like purchase receipts, ads, mailing lists, etc. and you teach inbox which of the mails you receive belong in there, just through the simple act of moving emails in and out.
Emails in those categories don't trigger notifications.
And for the kinds of emails you consider urgent, you move them out of the category they're in, let Inbox know "don't categorize this type of mail".
Only those trigger notifications.
The result of this is that your phone acts like a secretary on your emails. It sorts them into various inboxes for you so you can review them later on, or lets you know if something came in you might want to look at immediately. It's not perfect, sure, it's more akin to a 12 year old playing secretary. However it certainly stems the "tide" without forcing you to cut yourself off entirely, providing a nice medium you can use for normal work time, leaving DND mode for when you actually need exactly that.