A letter API that prints, stamps and mails through USPS
By Justin Winter · Updated October 21, 2026
The short answer
The letter API takes a PDF or text and a mailing address and returns a real letter in a mailbox. One page is $0.99 First-Class, $12.99 Certified Mail, or $14.99 with the electronic Return Receipt. Postage, paper and the envelope are included. The API returns a preview before you pay and a tracking number when the service includes it.
How it works
- Send the letter payload. POST the PDF or text, the mail class and the recipient address. The API returns a preview and a price.
- Confirm the send. Approve the price and the API hands the letter to the print facility.
- We print and mail it. The letter 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 |
|---|---|
| First-Class letter | $0.99 |
| Certified Mail letter | $12.99 |
| Certified Mail with electronic Return Receipt | $14.99 |
| Priority Mail letter | $24.99 |
Who it is for
- You are building a product that sends letters and want an API rather than a manual workflow.
- You need Certified Mail with a return receipt and want the API to handle the whole send.
- You want to test the pipeline end to end before committing to a contract.
When it is not the right tool
- You are sending postcards; use the postcard API 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 mail classes does the API support?
First-Class, Certified Mail, Certified Mail with electronic Return Receipt and Priority Mail. Each class is a separate SKU with its own price.
Can I send letters in bulk?
Yes. Send one POST per letter, or use a CSV mail merge. Each letter is priced on its own.
Where is the full API documentation?
The direct mail API docs cover letters, postcards and certified mail together, with endpoints, examples and webhook events.