Is there a one-to-one correspondence between ZIP codes and post offices? Meaning, for each ZIP code, is there one and only one post office that delivers all mail sent to that ZIP code? (Meaning, I could go to “my” post office and every letter loaded onto the trucks would have my ZIP code?)
And, if so, when a post office closes, does that mean ZIP codes must be reassigned?
I believe that was the original intent - the ZIP would identify the station/sub-station to which it would be delivered - where I live, there are two sub-stations I deal with - the closest one is too small to hold “will call” items, and the one where I pick up packages is not the same the one from which my carrier is based - that one is one I’ve never even seen.
The ZIP+4 is supposed to identify your block (or, presumably, your apt complex, if it is large enough)
I’m not sure about how it works in the States, but that is not the case at all with the postal codes in Canada. The postal codes here are so specific that they vary from pretty much block to block, and they also vary depending on the side of the street that you live on.
Canadian postal codes suck.
This drive by brought to you by someone who’s spent days sorting Canadian mail, where you have to look at three different alphanumeric fields, instead of U.S. where you have a 3 to 5 digit numberic code.
I’m on the sending end of things, rather than receiving, so I’m sorry I can’t be more helpful.
I’m almost positive this is the case in the U.S.
My college had a separate ZIP from the surrounding town, because it had a separate post office that did the final distribution.
I’ve heard many, many people complain that the Canadian postal system sucks, so I’ll stick with the USPS and its five digit ZIP codes.
Around here, all of the post offices have a sign on the side of the building which shows their ZIP code (ie, “UNITED STATES POST OFFICE 48185” or something like that). Do all post offices in the US do this?
My husband is a letter carrier in our town, so I’ll use the example from around here.
Way it used to be (and had been for quite some time): two towns sharing the same ZIP, with a main post office in the larger one and a branch post office in the smaller one. The main office got the mail for both from the distribution center, then sent the branch’s mail over via truck. So two offices had mail for the same ZIP code.
This changed in the last few years - the branch’s routes all got moved to the main office, but at about the same time, the larger town got its own ZIP code. So one office has the mail for two ZIP codes now, two different towns. (Actually, it has three ZIPs, as I gather the PO Box mail there has its own ZIP as well.)
This sort of means that no, ZIPs do not have to not have to be reassigned when a post office closes - the branch office is now only a place to sell stamps, ship packages/mail, and have PO Boxes.
At the same time, another post office was built nearby. It serves two towns, each of which has its own ZIP. The mail for those towns was previously split among other post offices.
Meanwhile, a nearby town has two offices in it. This town has only one ZIP, but one of those offices also handles mail for the neighboring suburb, which has a different ZIP. So mail for one ZIP is split between two offices, and one of those offices handles two ZIPs.
Confused yet?
He says the answer to your question is, “It all depends.” 
Only the ones that serve towns that are too small to have more than one zip code.
Like all the towns west of Detroit… 
It’s no longer the case (if it ever was) that there’s a one-to-one correlation between ZIP codes and post offices. For example, my main post office is 48093, and it’s the only post office that serves the city officially. My ZIP code within the same city is 48089. My city (not Detroit) has five or six ZIPs, I think. Furthermore, I think 48093 serves the entire city, since all of my title and mortgage documentation shows 48093, and my neighbors when I moved in told me 48093. So maybe it’s a “blanket” ZIP code for the entire city, that later gotten broken up into more precise ZIP codes. I only happen to know my ZIP+4 code because I called the post office to get my +4, and they told me I was in 48089 instead of 48093!
Maybe we need to get the Master involved to sort out this mess!
Additionally, the “hub” postoffice that actually postmarks all of the mail in southeast Michigan is Royal Oak, with their own ZIP code. I don’t go to my “official” post office for business, though, since the 48021 post office is very close to my house. I habitually use my +4 ZIP of 4164 – I don’t know if it really helps my mail get here faster or not. Anyone have an idea?
No.
Yes.
No.
Depends.
Many post offices serve two or more zip codes – e.g., a large city post office will have one zip code for delivery routes and one for P.O. boxes at that office. My former home town had a single zip code covering P.O. boxes and delivery routes (and was a regional subcenter as well) – but also served a nearby Army base with two additional zip codes. Though there was a substation located on base, their postmaster was based and most of the processing was done at the main P.O. in that town.
Such as L.A., S.F., Seattle, Denver, Chicago, etc.?
back atcha
Here in New York, certain buildings have their own ZIP codes. For instance, I work in the Lincoln Building, 60 East 42nd Street, which is ZIP code 10165. We don’t have any post office in the building.
Also, I had a client who was a major corporation in a small city. The corporation had its own ZIP code for its mail.
In addition to what Billdo says, which is true for virtually all large cities, not just NYC, many large cities have (or had - many are moving out to suburbs these days) central post offices that contained the routes for a number of centrally located zip codes. Why build many small buildings in a crowded downtown when one central facility offers many cost benefits?
The building I work in here in Washington DC has it’s own zip code, along with our own mail center down in the basement. I have found that I can get transcontinental letters and packages 3 days earlier at work then I can at home. Anyone know why?
FYI, the Pentagon has 4 zip codes.
My wild guess is that the distribution center for your home is different from the one for your workplace, and distance and/or efficiency issues between the centers cause the time delay. If it’s just transcontinental mail that’s delayed, then probably your workplace’s distribution center is located closer to the airport, and might have more frequent mail deliveries from there. Now that I think about it, maybe the mail from the airport gets routed through a different distribution center before getting to the one that serves your home.
Also, from my past experience working in a business that processed bill payments, I know that they would do special mail runs of their own at all hours to the mail distribution center - they’d be getting mail in at 11 pm, etc. Maybe your workplace has a deal set up, since they have their own ZIP, to just pick up their mail at the processing center.
My husband thought this was a reasonable guess, but says he couldn’t provide an absolutely “correct” answer.