https://www.tesla.com/en_CA/customer-stories/electric-mail
With an EV, it’s a function of route distance, not route time. Minnesota gets pretty cold! Also, an EV costs half per mile of a combustion vehicle.
Your next rural mail carrier (where the vehicle decision is local) could be driving a Model Y!
If you're doing a grand total of a 100 miles in those 8 hours, you sure can - and city delivery vehicles will do even less than that. Yes sure it won't work if you're driving hundreds of miles every day - but even with postal services that's extremely rare, those are last mile delivery trucks not long distance transporters
Even if we assume non-stop 8 hours of driving (which it obviously isn't for mail delivery), that's only ~185 miles of range in the absolute worst case scenario.
Well within the range of a modern EV.
From a cost-benefit perspective gas is still king. Otherwise you’ll need 1.5-2x EV trucks for every one gas powered.