A postcard API that prints and mails through USPS
By Justin Winter · Updated October 21, 2026
The short answer
The postcard API takes a message and a mailing address and returns a real postcard in a mailbox. A 4x6 is $0.99, a 6x9 is $2.99 and a 6x11 is $3.49. Postage, paper and printing are included. The API returns a preview before you pay and a tracking number when available.
How it works
- Send the postcard payload. POST the message, the size and the recipient address. The API returns a preview and a price.
- Confirm the send. Approve the price and the API hands the card to the print facility.
- We print and mail it. The card is printed and handed to USPS the next business day.
- Get the result. The API returns the status and any tracking information by webhook or poll.
What it costs
| Service | Price |
|---|---|
| 4x6 postcard | $0.99 |
| 6x9 postcard | $2.99 |
| 6x11 postcard | $3.49 |
Who it is for
- You are building a product that sends postcards and want an API rather than a manual workflow.
- You want to test the pipeline end to end before committing to a contract.
- You need one endpoint that covers design, printing and mailing.
When it is not the right tool
- You need a letter or a certified send; use the letter API or the certified mail endpoints instead.
- You are sending to addresses outside the US; the API covers USPS domestic delivery only.
- You need a monthly contract with volume discounts; the API is pay per send.
Keep reading
Questions before you send
If something goes wrong, do I pay?
If we cannot mail the letter, the hold on your card is released and you are not charged. If a letter fails after your card is charged, you are refunded automatically and in full.
Do I need an API key to start?
No. Every order carries its own payment: a credit code, or a paperplane payment link a human approves. An API key matters only if you want saved addresses or a billing relationship.
What sizes does the API support?
4x6, 6x9 and 6x11. Each size is a separate SKU with its own price.
Can I send postcards in bulk?
Yes. Send one POST per card, or use a CSV mail merge. Each card is priced on its own.
Where is the full API documentation?
The direct mail API docs cover postcards, letters and certified mail together, with endpoints, examples and webhook events.