Send Messages via API

{
  "to": "recipient@example.com",
  "cc": "cc@example.com",        // optional
  "bcc": "bcc@example.com",      // optional
  "subject": "Email Subject",
  "text": "Plain text body",     // optional if html provided
  "html": "<p>HTML body</p>",    // optional if text provided
  "attachments": [                // optional
    {
      "id": "att-123",
      "name": "document.pdf",
      "url": "/uploads/...",
      "type": "application/pdf",
      "size": 1024
    }
  ]
}

{
  "ok": true,
  "messageId": "msg-abc123"
}