---
title: "Send a reply on an existing thread."
method: POST
path: "/threads/{id}/reply"
tags: ["inbox"]
---

# Send a reply on an existing thread.

`POST /threads/{id}/reply`

## Request

- Base URL: `https://api.coldrig.dev`
- URL: `https://api.coldrig.dev/threads/{id}/reply`
- Auth: HTTP bearer

## Path parameters

- `id` string, required

## Request body

- ReplyInput
  - `body` string, required

## Response `201`

Reply sent (or a dedup replay — see `deduplicated` on the schema).

- ReplyResult
  - `messageId` string, required
  - `deduplicated` boolean, required: true means NO new email was sent — `messageId` is from an earlier send this call matched, either the SAME Idempotency-Key at any time, or (when no key is supplied) an identical body sent within the last 10 minutes. false means this platform sent the call onward as a NEW send. That is normally a new email, but it is NOT a guarantee one left the building: without an Idempotency-Key the body hash is matched HERE for 10 minutes only, while the sending provider keeps its own record of an identical body on the same thread for longer and can collapse a much later repeat into the original send. On such a repeat you may receive false together with the ORIGINAL send's messageId and no new email. Supply an Idempotency-Key, or vary the body, when a repeat must genuinely go out.

## Other responses

- `400`: Request body failed schema validation.
- `401`: Missing, invalid, or inactive bearer token.
- `409`: Reply refused by send governance, non-retryable: the recipient is suppressed, or the sending mailbox is deliverability-paused. Both need a state change before a retry can succeed.
- `429`: Reply refused by send governance, retryable: the sending mailbox has used its full daily send allowance. Retry after the daily counter rolls over.

---

[API](https://skmtc.dev/coldrig/apis/agent-cold-email-api.md) · [All operations](https://skmtc.dev/coldrig/apis/agent-cold-email-api/llms.txt) · [OpenAPI document](https://skmtc.dev/coldrig/apis/agent-cold-email-api/revisions/242a462d82c4?raw)