Postal Code Format vs. Address Deliverability
A format check can confirm that a postal code matches a pattern; it cannot confirm a complete, current delivery destination. A missing apartment, incorrect street, old recipient address or service restriction can remain after the postal field passes.
For developers and QA teams, the useful question is what evidence each check actually supplies. Keep those results separate in your interface and logs, so a green syntax result does not become an unsupported “delivery verified” label.
Four checks that answer different questions
| Check | What it establishes | What remains unknown |
|---|---|---|
| Postal syntax | The entered characters match maintained country rules. | Allocation, street match, building, unit and recipient. |
| Address matching | A provider returns one or more candidates from its address data. | Whether the candidate is complete, current or the intended destination. |
| Delivery-point validation | A particular postal database recognizes a delivery point within that service’s scope. | Recipient identity and the outcome of this specific shipment. |
| Actual delivery | A shipment event is reported by the carrier. | A universal guarantee for future mail or another service. |
USPS describes DPV as checking whether a ZIP+4-coded address is represented as a known delivery point. Its results can distinguish a recognized primary address with an unverified secondary component. DPV itself does not append missing data or correct address elements. AddressLab does not run DPV.
Our local rule accepts a pattern without looking up an address
On November 4, 2026 we ran three manually selected inputs through the US rule used by AddressLab’s local form-testing engine. No USPS or commercial address service was contacted:
| Input | Observed syntax result | Interpretation |
|---|---|---|
02108 | Pass | Matches the five-digit pattern; no street or recipient was supplied. |
2108 | Fail | Four digits do not match that rule. |
00000 | Pass | Also matches five digits. This test did not check postal allocation. |
The last row is deliberately illustrative, not a claim that 00000 is assigned or deliverable. A regular expression can accept the character structure while having no database knowledge. See the postal-code checker for the scope of its separate syntax and normalization interface.
What to check when an address cannot be verified or delivered
- Identify the source of the message. A field-length error, no-match response, missing-unit warning and carrier return reason require different actions. Save the exact message.
- Ask the recipient to confirm the full current address. Include country, street number, street, apartment/suite, locality, region and postal code where applicable. Check for an outdated address-book entry.
- Use the relevant postal or carrier lookup. Inspect candidates and secondary-unit findings rather than accepting the first approximate match.
- Check the selected service. A merchant’s delivery coverage and an address database are different systems. Confirm any restrictions with the merchant or carrier.
- For dispatched mail, follow the actual tracking or return reason. Updating an account address book does not establish that an in-transit parcel has been redirected.
USPS’s treatment of undeliverable mail includes incomplete or incorrect addresses and recipient-related circumstances. A historical match cannot establish that the same person still receives mail there.
A map pin is also a different kind of evidence from a postal record. Finding a building on a map alone does not establish the full unit, current recipient or acceptance by a particular delivery service.
Write separate expected outcomes in your test plan
For a syntax test, record the country, entered string, normalized value and exact rule result. For a provider integration test, record the provider, environment, candidate selection and returned status. For shipment tests, use the carrier’s own event identifiers. Avoid one undifferentiated valid: true field for all three.
Use the address form tester to test local field rules and the US fixture page to check save/export preservation. Neither provides recipient verification or live deliverability lookup. If a postcode changes during spreadsheet import, investigate the leading-zero problem before requesting another address match.
How this guide was checked
AddressLab prepared this English adaptation with AI assistance and checked the linked primary documentation and current local QA rules on November 4, 2026. The original Chinese guide is available here. Examples are synthetic fixtures or explicitly illustrative inputs. Local tests do not contact postal databases, card issuers or recipients. Report a discrepancy with the input, expected result and supporting reference through our contact page.