curl --request GET \
  --url https://app.sendmux.ai/api/v1/mailbox/threads/{thread_id} \
  --header 'Authorization: Bearer <token>'

{
  "meta": {
    "request_id": "req_clxxxxxxxxxxxxxxxxxxxxxxxxx"
  },
  "data": {
    "id": "<string>",
    "subject": "<string>",
    "message_count": 123,
    "unread_count": 123,
    "has_attachments": true,
    "folder_ids": [
      "<string>"
    ],
    "participants": [
      {
        "email": "agent@example.com",
        "name": "Support"
      }
    ],
    "last_message": {
      "id": "<string>",
      "thread_id": "<string>",
      "folder_ids": [
        "<string>"
      ],
      "subject": "<string>",
      "preview": "<string>",
      "from": {
        "email": "agent@example.com",
        "name": "Support"
      },
      "to": [
        {
          "email": "agent@example.com",
          "name": "Support"
        }
      ],
      "cc": [
        {
          "email": "agent@example.com",
          "name": "Support"
        }
      ],
      "bcc": [
        {
          "email": "agent@example.com",
          "name": "Support"
        }
      ],
      "received_at": "<string>",
      "sent_at": "<string>",
      "size_bytes": 123,
      "has_attachments": true,
      "keywords": [
        "$seen",
        "$flagged",
        "agent_triaged"
      ],
      "flags": {
        "seen": true,
        "flagged": true,
        "draft": true,
        "answered": true
      }
    },
    "states": {
      "thread_state": "<string>",
      "email_state": "<string>"
    },
    "message_ids": [
      "<string>"
    ]
  }
}