I have ATT. It hasn't ever worked before.
It started working today. I haven't driven the car in exactly 14 days because I was on a motorcycle trip then business trip.
I turned notifications off while on vacation as to not be bothered by work emails.
Turned it back in yesterday.
Left for work at 5:30am and didn't get any emails at that hour while on my 1 hour commute.
On my way home at 4pm. The emails were pouring in and showing in "notifications" on the screen in the car just like texts do.