Post service delivering that mail
With the Cities Skylines Industries DLC also came establishing a post service for the first time ever in your cities. That is build post shops to handle the local mail while the big central mail sorting centres do that sort the mail city-wide (including receiving/sending mail in/out of the City).
Running the post service is the same as other non-transit city services in Cities Skylines: place down your local post offices followed by central depots/centres in strategic locations (usually next to rail terminals). Rather interestingly your post van will use bus lanes just as any other city service vehicle does (unless banned by the Transport Manager President Edition) but the post truck will not (treated as a freight vehicle).
The Post Offices and Sorting Centre
As well as the standard post office and sorting centre I also got a Parisian version of a post office that fights into tight spaces better than the vanilla game version:
Of course here are the standard versions:
Standard post office 
Mail sorting centre
Post delivery run
Zeroing in on a post shop in Prospect District I decided to follow a post van around to watch its mail run. This is what we got:
French Post Office Standard post office 
Okay that did not go very far as the van dumped a pile of parcels at a retail store before returning to the post shop. Let’s try this again:
French Post Office 
The van was delivering across Prospect District, Wiri East and Wiri (industrial complex) so good way of seeing the urban form.
I need to place another sorting centre next to Papatoetoe to handle mail over in that part of the city. Otherwise here comes your deliveries by van, truck, rail, sea and air!
Ben's Cities 