Developer Mail API for Letters, PDFs, and Postcards

Yes. PostalForm Projects exposes a REST API at https://projects.postalform.com/api/v1 for sending letters and postcards from code. Every workspace includes a free simulated test environment, separate test and live API keys, final-price quotes, order timelines, carrier tracking when available, and signed webhooks.

Live mail uses prepaid credits with no subscription or minimum commitment. PostalForm selects an eligible print-and-mail route from the document, destination, speed, and proof-mail options in the quote request.

1. Create a workspace - Sign up directly or provision postalform/mail through Stripe Projects.
2. Upload the PDF - Create an upload intent, upload the bytes, and mark the document complete.
3. Request a quote - Choose print, speed, destination, and proof-mail options.
4. Create the order - Send the quote ID, recipient, and an idempotency key.
5. Observe fulfillment - Poll the order or consume signed webhooks as its status changes.

export POSTALFORM_API_KEY="pf_test_..."
export POSTALFORM_API_BASE="https://projects.postalform.com/api/v1"

curl -s "$POSTALFORM_API_BASE/letters/quotes" \
  -H "Authorization: Bearer $POSTALFORM_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"document_id":"doc_...","mail_class":"usps_first_class"}'

curl -s "$POSTALFORM_API_BASE/letters" \
  -H "Authorization: Bearer $POSTALFORM_API_KEY" \
  -H "Idempotency-Key: invoice-1042" \
  -H "Content-Type: application/json" \
  -d '{"quote_id":"quote_...","recipient":{"name":"Ada Lovelace","line1":"1 Analytical Way","city":"San Francisco","state":"CA","postal_code":"94105"}}'

The complete quickstart includes the PDF upload-intent flow, document completion, webhook setup, and test-to-live checklist. Read the five-minute quickstart.

• PDF document uploads with validation and reusable document records
• Standard, Priority, and Express letter options where eligible
• Black-and-white or color printing and simplex or duplex output where supported
• USPS Certified Mail, eligible registered-mail services, and return-receipt options
• Postcards in supported sizes from composed two-page artwork
• Domestic and supported international destinations
• Final-price quotes before order creation
• Idempotent letter and postcard orders
• Signed fulfillment webhooks, timelines, and tracking fields
• Prepaid live credits, balance reads, top-ups, and configurable auto-refill
• OpenAPI 3.1 schemas for client generation and integration review

PostalForm Projects is the persistent developer platform: workspaces, API keys, test and live environments, prepaid credits, webhooks, and mail timelines. Hosted checkout and MCP are separate integration paths for flows where a person or agent prepares a reviewable mailing before payment.

Many direct-mail APIs are designed for enterprise transactional output, CRM campaigns, or large marketing programs. PostalForm Projects is strongest when a developer needs a focused document-mail API with a free end-to-end test mode, transparent per-piece quotes, safe retries, and observable fulfillment.

Physical mail has offline consequences. PostalForm Projects keeps production sends explicit and observable:

1. Use a test key until the complete integration passes against simulated fulfillment.
2. Request a quote before creating an order.
3. Reuse the same idempotency key when retrying the same order.
4. Verify the PostalForm-Signature header before trusting webhook payloads.
5. Use live keys only when the application is authorized to spend prepaid credits and send real mail.
6. Do not use PostalForm to send spam, harassment, illegal content, or documents the sender is not authorized to mail.

• PostalForm Projects API reference
• PostalForm Projects OpenAPI specification
• PostalForm Projects machine-readable context
• PostalForm MCP endpoint and agent integrations
• Lob API documentation
• PostGrid Print & Mail API documentation
• Postalytics Direct Mail API
• Click2Mail API documentation