The primary surface is the REST API and the MCP server.

POST /v1/messages with Idempotency-Key.

Fixes Message-ID and Date, hashes the exact byte stream that will go over the wire, and will not re-send if you replay the same key. Body accepts from, to, subject and html.

curl -X POST https://api.mailack.com/v1/messages \
  -H "Authorization: Bearer $MAILACK_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -H "Content-Type: application/json" \
  -d '{
    "from": "noreply@acme.mx",
    "to": "cliente@ejemplo.com",
    "subject": "Estado de cuenta",
    "html": "<p>Tu estado de cuenta está listo.</p>"
  }'

Status, proof bundle and on-demand sealing.

Read the message, download the proof package (hash, Merkle path, certificate) or request an individual seal when you need one.

curl -s https://api.mailack.com/v1/messages/$MESSAGE_ID \
  -H "Authorization: Bearer $MAILACK_API_KEY"

curl -s https://api.mailack.com/v1/messages/$MESSAGE_ID/proof-bundle \
  -H "Authorization: Bearer $MAILACK_API_KEY" \
  -o bundle.json

curl -X POST https://api.mailack.com/v1/messages/$MESSAGE_ID/seal \
  -H "Authorization: Bearer $MAILACK_API_KEY"

Check it without taking our word.

POST /v1/verify recomputes the inclusion proof from the API. And whoever receives a bundle can check it at mailack.com/verificar: the verification runs in their browser, with nothing uploaded.

curl -s -X POST https://api.mailack.com/v1/verify \
  -H "Authorization: Bearer $MAILACK_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"message_id": "'"$MESSAGE_ID"'"}'

Agents that send, query, verify and operate.

mailack-mcp exposes MCP tools over the same API: send messages, read status, fetch proof bundles, verify and run allowed operations (suppression, event lookup).

Add the server to the MCP client you use (Claude Desktop, Cursor or any stdio-capable host). Auth is the API key in the process environment.

{
  "mcpServers": {
    "Mailack": {
      "command": "./bin/mailack-mcp",
      "env": {
        "MAILACK_API_KEY": "mlk_...",
        "MAILACK_API_URL": "https://api.mailack.com"
      }
    }
  }
}

Six processes, one evidence contract.

Each service has a narrow role. Delivery does not depend on the LLM; sealing never re-serializes the MIME.

RLS, suppression and VERP correlation.

PostgreSQL with Row Level Security. Each tenant only sees its rows. Working tables are messages, batches, events, suppressions and access_log.