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Comment by thih9 | Hacker News Reader

What happens when I share my code with others? I.e. when there are multiple letters with the same code found in an outgoing post box?

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For all mail except the first, the same thing that happens if you send a letter with no postage: the sender will receive a request to pay after delivery. If the sender is unknown the recipient will receive a request to pay (which can be appealed).

I mail a fair amount of physical media using the postzegelcode. If you put a return address, PostNL just returns the letter with a sticker on it saying the postage was not enough. They won't deliver it.

If they deliver the letter to the return address, what prevents you from writing the target address as the return address and getting it delivered for free?

They know approximately the area the return address should be at, and they also know who used the app to buy the code.

It's also some kind of fraud in most jurisdictions, or subject to an extra fee if discovered.

Germany's new stamps aren't stamped any more - a QR code gets scanned and logged instead - so people thought they were lucky when they received unstamped letters and decided to re-use the stamp. They got hit with a fine.

What if the postal system has a bug - and one of these people used a newly bought stamp? Rare but not unheard of[1].

[1]: https://amp.cnn.com/cnn/2024/01/13/business/uk-post-office-f...

IIRC the first envelope scanned at a sorting facility invalidates the postzegelcode immediately, any envelopes using it after that will be handled like they had no postzegel at all (receiver has to pay)

What if you mail 2 and they are scanned at the same time and the database isn't up to date yet?

Seems strange they would design a system that could scan faster than they could process the DB, no? I assume there's some queue in between. But the real answer is probably just: multiple scans happen for the same piece of mail. Eventually, one or both of them will be marked as due for payment. The question then becomes, was it worth saving the postage cost for what is potentially a much costlier penalty?

You may find they will refuse service to you for unspecified reasons.

This seems fairly unlikely to ever occur. The database would have to be decentralized, and the two items would have to be mailed from separate locations and both be scanned more or less simultaneously—or within however many minutes it takes for database changes to propagate, which can’t be all that long since you’re able to buy a code and use it on the same day.

Given how remote the probability of this happening is, simply ignoring it and delivering both pieces probably isn’t unreasonable. Or flag it for further investigation and maybe bill the sender or recipient for an additional piece of mail.

And even if for some reason it does occur more often, a message queue is a common, and rather simple solution for this.

I would guess that the system generates more digits - lets say 3

when the postal system checks that PZC on the mail, if there is nothing written by the PZC then it's assumed to be fresh, and the 3 extra digits are looked up via a postal-service-only gateway, then placed on the mail by the PZC for future lookups, possibly along with a date.

If the PZC has the extra digits, then it can be looked up and confirmed as redeemed with those extra digits, and possibly the stamped date.

The extra digits could be stamped or handwritten, possibly with the postmark date used as the redemption date manually entered from the mail as it passes through the sorting system the first time, OR stamped from the date it's registered as redemption, either would work.

Such a system would relatively guarantee that fraud would be difficult, since only one person could have a PZC without the check digits go into the system, and sharing would be useless.

Only the first one would be legal and the recipients would have to pay for the postal cost of the next one. If you put the origin (postal code plus home number is enough) on the back you get a payment proposal in your mailbox.

The typical outgoing mail box, where you put your mail in for it to be delivered, doesn't allow peering into it. So a physical measure to avoid that. But if it's out in the open: first come first serve, like the other comments describe

1. Buy an apartment next to a well lit outgoing post box.

2. Install a system of mirrors to peek at the letters being inserted into the box

3. Reuse one code for a 50% chance of saving 1 euro and delivering your mail for free.

4. Send each letter 7 times, each with a different duplicate code, for a 99% chance of at least one free delivery.

Not worth the effort and I’m sure this would be tracked and stopped immediately. But it’s cool that in theory this seems possible.

If you are willing to go that length, I'll give you a damn postzegelcode

In my experience it will be delivered and the sender will be politely asked to pay for it. They don't have to pay for it but it's rude not to.

> They don't have to pay for it but it's rude not to.

Given that this is the Netherlands, that sounds like "they won't pay for it".

Many people think they have to pay.

Hmm. When was this? I've had the code read wrong a few times and they just have returned the letter. Then I've gotten a refund for the postage through their customer service.

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