Address verification on every letter
By Justin Winter · Updated August 22, 2026
Before we print anything, we run the recipient address through a USPS-standardized deliverability check — the same kind of validation carriers use to know whether an address is real and mailable. If it comes back undeliverable, we stop and tell you why instead of printing, stamping, and mailing a letter that was never going to arrive.
Physical mail has a failure mode that email does not: a bad address does not bounce back into your inbox with a note explaining why. It just gets marked undeliverable-as-addressed, and by the time anyone notices, the postage, printing, and handling are already spent. We built address verification into the order path itself so that failure happens before you pay for a letter that was never going to arrive, not after.
What actually happens when you place an order
Every non-sandbox order runs the recipient address through a live deliverability check before a single page is queued for printing. That check does three things:
- Confirms the address exists and matches a deliverable USPS record — not just that the ZIP code is real.
- Standardizes the format (correct abbreviations, unit designators, ZIP+4) to the version USPS carriers actually route on.
- Flags anything it cannot resolve — a missing apartment number, a transposed digit, a street that does not exist in that city — before printing starts.
If the address is undeliverable as entered, the order stops with a specific reason (bad street number, unmatched ZIP, address not found) instead of getting mailed anyway. If the address is valid but slightly off in formatting — the kind of thing that would otherwise slow a piece down at a sorting facility — we mail to the corrected, USPS-standardized version automatically. Either way, nothing prints until the address has passed the check.
Why this matters more for physical mail than for email
| Failure | Physical mail without verification | |
|---|---|---|
| Bad address | Bounces back immediately, usually with a reason. | Silently discarded or returned days later, after printing and postage are spent. |
| Cost of a miss | Effectively zero. | Full price of the letter — paper, printing, and USPS postage — for nothing. |
| Who finds out | You, right away. | Sometimes no one, until a follow-up never gets a response. |
Catching a typo before printing is the difference between a five-second correction and a wasted $1.99–$24.99 letter, depending on the mail class you chose.
Autocomplete while you type, verification when you send
These are two different things, and it is worth being precise about which is which. The address autocomplete on our send form (and the corresponding /v1/address/autocomplete and /v1/address/reverse endpoints for API users) is suggestion data — it helps you get to a plausible address quickly as you type, or fill one in from a location. It is not, on its own, the deliverability check. The actual verification — the one that can reject or correct an address — runs separately as part of placing the order, against a dedicated deliverability provider, immediately before anything is printed. Autocomplete makes data entry faster; verification is what keeps a bad address from turning into a wasted letter.
This is not a standalone address-verification product you can buy or call on its own — paperplane sends letters, and address verification is the safeguard built into every one of them, not a separate service.
Related: see what counts as proof of mailing once your letter is on its way, or the full Certified Mail explainer if you need delivery tracking on top of a clean address.
Common questions
Do I need to verify the address myself before sending?
No — it happens automatically on every order, at no extra charge and with no separate step for you to run. You type or paste the address, we check it before printing.
What happens if my address is wrong?
If the check comes back undeliverable, the order stops before printing and you get a specific reason (bad street number, unmatched ZIP, address not found) instead of a charge for a letter that would have bounced. Fix the line that is wrong and resubmit.
What if the address is right but formatted a little differently than USPS prefers?
That is the more common case, and it is handled without any action from you: when the check finds a valid address with a small formatting difference — a missing suite designator, an abbreviated street type, a ZIP+4 you did not include — we mail to the USPS-standardized version automatically. You do not need to fix anything or resubmit.
Is there a standalone address-verification API, separate from sending a letter?
Not as its own billed product — verification is a step inside every send, not something you can call in isolation. If you build against the paperplane API, the address autocomplete and reverse-geocoding endpoints help you collect a clean address at data-entry time, but the deliverability check itself runs as part of placing the order, using a different, authoritative provider check.