The unreliable mail service issue is a wierd one.
I am pretty sure there is a bug or something is not working an intended even after the patch yesterday.
Sometimes when I load my city up my mail processing centres seem to be working and my residents stop complaining so much.
Othertimes they sit there at NIL processing.
I don't change anything, I can only think of sometimes when I load up the city something doesn't kick in.
Very wierd as my city is running well with no other real problems other then the mail service. Hopefully it gets fixed properly on the next patch.
Agreed, im not entirely sure what the large sorting office is supposed to do. It clearly has a different type of role, but like you say it seems to be very stop-start.
The Post Office is 100% local, gets mail from mailboxes and seems to deliver to commercial buildings.
The Sorting Facility is 100% outside. I thought maybe it collects the mail from the Post Offices, but if it does, it doesnt do it nearly frequently enough.
Im wondering if its another one of these instances where it sits idle and looks bugged, but its simply waiting for a threshold value to be met somewhere (ie 50,000 mail at a Post Office) before it sends a large truck to collect it. It only has 5 vehicles at vanilla, so it cant be constantly dashing off for 10k mail. [Edit - 50/100k hit and nothing happened, so still guessing what these SF vehicles move for]
I also dont fully understand how the cargo terminals play into things. Theres 'Local Mail' and 'Unsorted Mail' and im not really sure who picks up what there. The sorting facility mentions unsorted mail, and im pretty sure i saw my SF pop over the road to get unsorted mail immediately. None of my terminals have unsorted currently, but they all have about 400T local mail, so maybe i need a PO closer to them, to deal with that. Im sure ive done this before, but maybe it wasnt collecting the unsorted mail and the distinction between the 2 were lost on me at the time.
Edit #2 - Also, my SF has 32k mail in there, just sitting. 21k local mail and 11k global mail. Why, where does it go, when will it go...?
Edit #3 - The Post Office takes 'Local Mail' from the cargo terminal, in 25t deliveries. Just watched 2 truck loads get delivered (took the road that goes all the way around the building, to deliver to its neighbour - they literally touch each other!) so maybe i need a couple more purely to deal with the mail in there.