# Reply to a thread message

`POST /v1/email/threads/{thread_id}/messages/{message_id}/reply`

Sends a reply to a specific message in a conversation, from the mailbox's own address. Recipients are derived from the message being replied to: for a received message, its Reply-To address when present, otherwise its From address; for a message the mailbox sent, its original To recipients. Set `reply_all` to copy the original To and Cc recipients in as `Cc`, leaving out the mailbox's own address. The subject and the threading headers that keep the reply in this conversation are set automatically, and the reply is recorded in the conversation. To reply to a conversation as a whole, target its newest received message.

## Code samples

**TypeScript**

```ts
const reply = await bird.email.threads.messages.reply("thr_01abc", "rem_01xyz", {
  text: "Thanks for reaching out!",
});
console.log(reply.id);
```

Examples: [TypeScript](/docs/api/reference/reply-email-thread-message.ts.md) · [Python](/docs/api/reference/reply-email-thread-message.py.md) · [Go](/docs/api/reference/reply-email-thread-message.go.md) · [PHP](/docs/api/reference/reply-email-thread-message.php.md) · [CLI](/docs/api/reference/reply-email-thread-message.cli.md) · [MCP](/docs/api/reference/reply-email-thread-message.mcp.md) · [cURL](/docs/api/reference/reply-email-thread-message.curl.md)

## Example response `202`

```json
{
  "id": "rem_01krdgeqcxet5s7t44vh8rt9mg",
  "direction": "inbound",
  "channel": "email",
  "thread_id": "thr_01krdgeqcxet5s7t44vh8rt9mg",
  "subject": "Re: Your order",
  "labels": [
    "inbox",
    "unread"
  ],
  "recipients": [
    {
      "status": "delivered"
    }
  ],
  "authentication": "pass",
  "attachment_manifest": [
    {
      "id": "rea_01krdgeqcxet5s7t44vh8rt9mg",
      "filename": "invoice.pdf",
      "content_type": "application/pdf"
    }
  ],
  "contact_id": "con_01krdgeqcxet5s7t44vh8rt9mg",
  "source": {
    "resource": "/v1/email/inbound-messages/rem_01krdgeqcxet5s7t44vh8rt9mg"
  }
}
```

## Path parameters

- `thread_id` (string): Thread identifier. Starts with `thr_`.
- `message_id` (string): Message ID (`rem_` for a received message, `em_` for a sent one).

## Request body

- `html` (string): HTML body of the reply. At least one of html or text must be provided.
- `text` (string): Plain-text body of the reply. At least one of html or text must be provided.
- `reply_all` (boolean): Also send the reply to the original To and Cc recipients, minus the mailbox's own address.
- `tags` (array of object): Structured `{name, value}` labels for filtering and analytics on the sent-message log. Cap: 20 tags per send.
- `tags.name` (string, required): Tag name. ASCII letters, digits, underscore, and hyphen only. Case-sensitive. Maximum 32 characters.
- `tags.value` (string, required): Tag value. ASCII letters, digits, underscore, and hyphen only. Case-sensitive. Maximum 64 characters.
- `metadata` (object): Arbitrary JSON object stored on the send and echoed in webhook payloads. Cap: 2 KB serialized.
- `category` (string)

  Content classification, which controls suppression policy:

  - `marketing`: Blocks on all suppression reasons.
  - `transactional`: Allows delivery through complaint and unsubscribe suppressions, for receipts, password resets, and similar operational mail.

  Possible values: `marketing`, `transactional`
- `attachments` (array of object): File attachments to include with the reply. The send is rejected when the estimated generated message size exceeds 20 MB (bodies plus all attachments after base64 encoding). Keep total raw attachment content at or below 15 MB for reliable headroom. Attachment metadata stays on the message's `attachment_manifest`, and the bytes are downloadable for the mailbox's retention tier.
- `attachments.filename` (string, required): The name the recipient sees on the attachment.
- `attachments.content` (string, required): Base64-encoded file bytes. The encoded value and MIME wrapping count toward the 20 MB message limit.
- `attachments.content_type` (string): The file's MIME type. If omitted, the API infers it from the extension in `filename`. The API rejects executable and script types based on this value.
- `attachments.content_id` (string): An RFC 2392 Content-ID for an inline file. Reference it from the HTML body with `<img src="cid:{content_id}"/>`. Omit it to send a downloadable attachment.

## Response body

- `id` (string, required): Message ID. Received messages have a `rem_` ID, sent messages an `em_` ID: the same IDs used by the received-message and sent-message logs.
- `direction` (string, required)

  Which way the message went. `inbound` means you received it, `outbound` means you sent it.

  Possible values: `inbound`, `outbound`
- `channel` (string, required): Channel this message lives on. Always `email`.
- `thread_id` (string, required): Conversation this message belongs to.
- `from` (string, required): Sender address.
- `to` (array of string, required): Recipient addresses on the To line.
- `cc` (array of string, required): Recipient addresses on the Cc line. Empty when the message had none.
- `delivered_to` (nullable string, required): Address the message was actually delivered to, when it differs from the mailbox address (for example mail routed in from another address). Null for sent messages and for mail addressed directly to the mailbox.
- `subject` (nullable string, required): Message subject. Null when the message had no subject.
- `preview` (nullable string, required): Short plain-text preview of the message body.
- `extracted_text` (nullable string): Plain-text content of the message with quoted history stripped. Readable for the mailbox's full retention tier, in both directions. Always present when fetching a single message. On list endpoints it is included only when the request sets `include=extracted_text`. Null when no text could be extracted.
- `labels` (array of string, required)

  Labels on this message. A received message always has exactly one placement label:

  - `inbox`: Accepted mail.
  - `archive`: The message's conversation was filed away.
  - `spam`: The message is filed in Spam.
  - `blocked`: The message was rejected by the mailbox's receive policy or rules.

  A received message also has `unread` until it is read. `trash` marks a message in the trash, in either direction. Custom labels share the same list, and a message has at most 20 labels in total.
- `status` (nullable string, required)

  Aggregate delivery status of a sent message:

  - `accepted`: Accepted for sending.
  - `sent`: Handed off to the provider.
  - `delivered`: All attempted recipients delivered.
  - `failed`: Terminal failure.

  Null for received messages.
- `recipients` (nullable array, required): Terminal per-recipient delivery outcomes of a sent message, filled in as each one becomes known and kept for the mailbox's full retention tier. Null for received messages and before any recipient reaches a terminal state. Per-recipient event detail lives on the sent-message log (`source`) for 30 days.
- `authentication` (nullable string, required)

  DMARC result for the domain in the received message's `From` header.

  - `pass`: SPF or DKIM passed and aligned with that domain.
  - `fail`: DMARC was evaluated and did not pass.
  - `unknown`: no trustworthy verdict is available.

  This follows `dmarc_pass` and does not verify a particular person. The receiving provider currently supplies no DMARC result, so received messages report `unknown`.

  Null for sent messages. This field is readable for the mailbox's full
  retention tier, so the verdict is still available after the 30-day
  received-message log has expired.

  Possible values: `pass`, `fail`, `unknown`, `null`
- `spf_pass` (nullable boolean, required): Whether the receiving provider reports that SPF authorized the envelope sender for the sending server. A soft failure is `false`. Missing, neutral and inconclusive results are `null`. Sent messages have `null` results. Kept for the mailbox retention tier.
- `dkim_pass` (nullable boolean, required): Whether the receiving provider verified a DKIM signature. A passing signature makes this `true` even when another signature fails. Missing signatures and inconclusive verification results are `null`. Sent messages have `null` results. Kept for the mailbox retention tier.
- `dmarc_pass` (nullable boolean, required): Whether SPF or DKIM passed and aligned with the domain in the message's `From` header. The receiving provider currently supplies no DMARC result, so this is `null`. Sent messages have `null` results. Kept for the mailbox retention tier.
- `purge_at` (string, required): Scheduled permanent-deletion time. This is the end of the mailbox's retention tier, moved to no more than 30 days in the future while the message is in the trash. Restore a trashed message before then with `PATCH {"labels": {"remove": ["trash"]}}`.
- `attachment_count` (integer, required): Number of attachments on the message.
- `attachment_manifest` (array of object, required): Attachment metadata (filename, content type, size). Both the metadata and the attachment bytes stay available for the mailbox's retention tier.
- `attachment_manifest.id` (string, required): Attachment ID, used to download the attachment bytes.
- `attachment_manifest.filename` (nullable string, required): Original filename, or null when the attachment had none.
- `attachment_manifest.content_type` (nullable string, required): MIME content type, or null when it could not be determined.
- `attachment_manifest.size` (integer, required): Attachment size in bytes.
- `reference_ids` (array of string, required): RFC 5322 References header entries used to thread the conversation.
- `contact_id` (nullable string, required): Contact linked to this message, or null when none is linked.
- `source` (object, required): Link to the message's entry in the received-message or sent-message log, which has delivery analytics such as per-recipient events. Log entries expire 30 days after the message occurred.
- `source.resource` (string, required): API path of the log entry for this message.
- `source.available_until` (string, required): When the log entry (and the message's body and raw MIME) expires.
- `occurred_at` (string, required): When the message was received or accepted for sending.

## Related resources

- [Getting started with email](/learn/email/getting-started-with-email) (video)
- [Email](/email-api) (product)
- [Build your first integration](/learn/paths/integration) (course)
- [Send your first email](/docs/get-started/send-your-first-email) (docs)

[Get an implementation brief](/learn/workspace?topic=email)