Print and mail API for letters

Send a letter from your app the way you send an email. Post a PDF and an address to the Sprint Mail API, and we print, seal and mail it by USPS First-Class. Every letter shows up in our tracking portal, for you and for the person you mailed.

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POST https://api-staging.sprintmail.io/api/order
x-api-key: YOUR_STAGING_KEY

{
  "externalId": "order-1001",
  "sender": "Acme Corp",
  "letters": [{
    "recipient": "Jane Doe",
    "address": "123 Main St",
    "city": "Austin", "state": "TX", "zipCode": "78701",
    "fileUrl": "https://files.acme.com/invoice-1.pdf",
    "pages": 2
  }]
}

Staging orders never print. Test the whole flow first.

From your API call to their mailbox

  1. You post the order

    POST /order

  2. We print and seal it

    El Paso, Texas

  3. USPS First-Class

    Usually 4 to 7 business days

  4. Delivered

    Tracked the whole way

The Letter updates webhook calls you at every step.

The endpoints you will use

An order carries as many letters as you need. You pay once for the order, and it prints after payment.

  • POST /order

    Mail a whole batch

    One order, as many letters as you need, each with its own recipient and PDF. Send the same externalId twice and it is caught as a duplicate, never a second batch of mail.

  • POST /order/price

    Price before you send

    The cost from each letter's page count, before anything is created.

  • POST /address/check

    Check addresses first

    Runs your recipients past USPS before you mail to them.

  • POST /template/{id}/send

    Mail a template

    Store a letter once and mail it to a new recipient with one call.

  • HOOK Letter updates

    Webhooks

    A callback as each letter is printed, shipped and delivered.

Ready to mail from your software?

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Or let an AI agent do it

The same API powers the Sprint Mail MCP server. Connect your agent and ask it to mail a letter. Every send starts with a preview you can check.

See How the MCP Server Works
  • Claude
  • ChatGPT
  • Cursor
  • Meta Muse

Why teams mail with Sprint Mail

  • 4,000+

    orders every day

  • USPS

    First-Class Mail

  • Tracking

    on every letter

  • 4.98/5

    satisfaction score

Questions

The short answers. Anything else, ask in your application and we reply within 2 business days.

Can I test before I mail for real?

Yes. Approved partners start with a staging key, for the API and the MCP server. Staging orders never print, and our team can move one to production for you. Then you get a production key. Apply here.

How is it priced?

Letters start at $1.75 for the first page.

What can I mail?

Letters from a PDF, in black and white or color, to US addresses.

Do you offer Certified Mail?

Not yet. Certified Mail might be coming soon. For now, we add features as our users and partners request them.

Mail from your software

API keys go to approved partners. Tell us your monthly volume when you apply, and we will quote by volume.

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