To me, urban package delivery vans are a perfect use for electric power. I would love to see the Postal Service use electric vehicles for suburban mail delivery instead of the beat up old jeeps that they current use to deliver mail. But I doubt they can afford to replace those long-suffering smog machines. Too bad the mail can't be delivered on Postie Bikes like they use in Australia. 
There's actually no reason in can't be, in urban environments (probably cargo bicycles these days, with much/most post being packages, but ); it would most likely be both cheaper and faster. e-bicycles are getting cheap; cargo one start
below $2000, and of course ongoing maintenance is nearly negligible. Even larger cargo trikes aren't that expensive, compared to cars: E.g., the
RadBurro with 700lbs payload is $6K-$7K
Re overall delivery, in 2016 USPS announced a
$6.3B Tender/competition for their Next Generation Delivery Vehicle, to replace 180K of their last-mile vans.
Only one of the 6 shortlisted entrants was electric (5-6 prototypes of each were built and paid for by USPS) -- a joint effort between Workhorse (EV drivetrain) and VT Hackney (the body).
In the meantime, USPS has been dragging its feet about announcing a winner (originally, the trucks were supposed to go into service in 2019), delaying the decision several times, and then announcing they might split the contract -- as a result, several contenders dropped out, including Workhorse's partner.
The entire project now seems to be in
some doubt.
The whole project was clearly fumbled; too bad since there's already lots of previous experience they could have learned from.
The German Postal Service (which also owns DHL) has
10K StreetScooter LCVs (it actually bought the company to produce them, although they have now given up on making it a business in its own right).
The French Post has 7000 electric LCVs (mostly Renault Kangoos, some bigger ones), and 8000+ 3-wheeled & 4-wheeled electric sccoter/quad vehicles (also 21K e-bicycles).
