Threads

Threads group related messages into conversations. List threads for a mailbox, view messages in a thread, or reply to an existing thread.

Last updated May 13, 2026

The thread object

{
  "object": "thread",
  "id": "thr_abc123",
  "mailbox_id": "mbx_abc123",
  "subject": "Re: Pricing question",
  "message_count": 3,
  "latest_message": {
    "object": "message",
    "id": "msg_latest",
    "mailbox_id": "mbx_abc123",
    "thread_id": "thr_abc123",
    "subject": "Re: Pricing question",
    "from_address": "customer@example.com",
    "to_addresses": [{"address": "hello@example.com"}],
    "cc_addresses": null,
    "bcc_addresses": null,
    "attachments": null,
    "source": "inbound",
    "status": "delivered",
    "created_at": "2026-05-13T10:00:00.000Z",
    "updated_at": "2026-05-13T10:00:00.000Z"
  },
  "created_at": "2026-05-12T10:00:00.000Z",
  "updated_at": "2026-05-13T10:00:00.000Z"
}

List threads

GET /v1/threads?mailbox_id=mbx_abc123

Scope: threads:read. Rate limit tier: read.

The mailbox_id query parameter is required. Supports cursor and limit pagination parameters.

Returns a paginated list of thread summaries, ordered by the latest message in each thread.

Retrieve thread messages

GET /v1/threads/:id

Scope: threads:read. Returns a paginated list of messages in the thread. Supports cursor and limit parameters.

Reply to a thread

POST /v1/threads/:id/reply

Scope: messages:write. Rate limit tier: send. Sends a reply using the same mailbox as the latest message in the thread.

Request body

Field	Type	Required	Description
html	string	*	HTML body. Max 512 KB.
text	string	*	Plain text body. Max 256 KB.
to	recipient[]	Yes	To recipients. At least one required.
cc	recipient[]	No	CC recipients.

* At least one of html or text is required. Total recipients (to + cc) must not exceed 50.

Returns the message object with status 201.