# PUT /inboxes/{inbox_id}/threads/{thread_id}/labels (Resend API)
Base URL: https://api.resend.com
Auth: Authorization: Bearer <RESEND_API_KEY>
Last verified: 2026-10-20

> Set the labels of an inbox thread

## Critical Gotchas
* All requests must include a `User-Agent` header (e.g. `User-Agent: my-app/1.0`) or the API returns HTTP 403.

## cURL
curl -X PUT 'https://api.resend.com/inboxes/inbox-id/threads/thread-id/labels' \
  -H "Authorization: Bearer $RESEND_API_KEY" \
  -H 'User-Agent: my-app/1.0' \
  -H 'Content-Type: application/json' \
  -d '{"labels":["7f9c1d2e-4a6b-4c3d-8e15-9b0a7c6d5e34"]}'

## Parameters
| Name | In | Type | Required | Description |
| :--- | :--- | :--- | :--- | :--- |
| inbox_id | path | string | Yes | The Inbox ID or the inbox email address, such as `support... |
| thread_id | path | string | Yes | The Thread ID. |
| labels | body | string[] | Yes | The IDs of the labels the thread carries after the change... |

## Response (200 OK)
{"object":"list","data":[{}]}

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