List thread messages

Example response

{
  "data": [
    {
      "attachments": [
        {
          "content_type": "application/pdf",
          "disposition": "attachment",
          "download_url": "https://app.sendmux.ai/api/v1/mailbox/messages/msg_123/attachment-downloads/attref_abc123?download_token=...",
          "filename": "invoice.pdf",
          "size_bytes": 12345
        }
      ],
      "bcc": [
        {
          "email": "agent@example.com",
          "name": "Support"
        }
      ],
      "cc": [
        {
          "email": "agent@example.com",
          "name": "Support"
        }
      ],
      "from": {
        "email": "agent@example.com",
        "name": "Support"
      },
      "keywords": [
        "$seen",
        "$flagged",
        "agent_triaged"
      ],
      "to": [
        {
          "email": "agent@example.com",
          "name": "Support"
        }
      ]
    }
  ]
}