> ## Documentation Index
> Fetch the complete documentation index at: https://deepline.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Resend: Inboxes Reply Thread Email

> Reply to a thread email. Includes SDK V2 and CLI requests, input constraints, response fields, and Deepline credit cost.

Reply to a thread email.

> [!NOTE]
>
> Tool ID: `resend_inboxes_reply_thread_email`

## Run this action

Use the TypeScript SDK for one call. Use `ctx.tools.execute(...)` inside a Play for durable calls, scheduled calls, or CSV processing.

```ts theme={"languages":{"custom":["/languages/deepline-prompt.json"]}}
import { Deepline } from 'deepline';

const deepline = await Deepline.connect();
const result = await deepline.tools.execute(
  'resend_inboxes_reply_thread_email',
  {
    "inbox_id": "inbox_123",
    "thread_id": "123e4567-e89b-42d3-a456-426614174000",
    "email_id": "123e4567-e89b-42d3-a456-426614174000"
  },
);

console.log(result.toolResponse.raw);
```

### CLI

```bash theme={"languages":{"custom":["/languages/deepline-prompt.json"]}}
deepline run resend_inboxes_reply_thread_email --input '{
  "inbox_id": "inbox_123",
  "thread_id": "123e4567-e89b-42d3-a456-426614174000",
  "email_id": "123e4567-e89b-42d3-a456-426614174000"
}'
```

## Example response

The SDK returns this shape at `result.toolResponse.raw`. The example values illustrate the response.

```json theme={"languages":{"custom":["/languages/deepline-prompt.json"]}}
{
  "data": {
    "id": "123e4567-e89b-42d3-a456-426614174000"
  }
}
```

Use `deepline describe resend_inboxes_reply_thread_email --json` for the latest machine-readable contract.

## Input reference

At least one of `html` or `text` must contain more than whitespace.

| Name | Type | Required | Default | Details |
| - | - | - | - | - |
| `payload.inbox_id` | `string` | Yes | — | The Inbox ID or the inbox email address, such as `support@acme.com`. A value that contains `@` must be a valid email address, and any other value must be a UUID, or the request returns a 422. The address match is case-insensitive and never falls back to the inbox `name`. An address that matches no inbox returns a 404. |
| `payload.thread_id` | `string` | Yes | — | The Thread ID. Format: `uuid`. |
| `payload.email_id` | `string` | Yes | — | The Email ID of the message to reply to, as returned in `data[].id` by the list thread emails endpoint. Format: `uuid`. |
| `payload.cc` | `string \| array \| null` | No | — | CC recipient email address. For multiple addresses, send as an array of strings. Without `reply_all`, the reply copies only these addresses. With `reply_all`, these addresses are merged with the copied recipients, without duplicates. `cc` and `bcc` combined must be fewer than 50 addresses. After the `to` recipients are added, the reply cannot exceed 50 recipients. Each address is `email@example.com` or `Name `. An address that is not valid returns a 422. |
| `payload.bcc` | `string \| array \| null` | No | — | BCC recipient email address. For multiple addresses, send as an array of strings. BCC recipients of the original message are never copied. Each address is `email@example.com` or `Name `. An address that is not valid returns a 422. |
| `payload.html` | `string` | No | — | The HTML body of the reply. |
| `payload.text` | `string` | No | — | The plain-text body of the reply. |
| `payload.subject` | `string` | No | — | The subject of the reply. Cannot be only whitespace or contain a line break. When omitted, the thread subject is used, prefixed with `Re:` if it does not already start with it. Minimum length: 1. Maximum length: 2000. |
| `payload.reply_all` | `boolean` | No | `false` | Reply to everyone on the original message. For a message the inbox received, the reply goes to its `Reply-To` addresses, or to its sender when it has none, and copies the other addresses of its `To` header and its `cc` recipients in `cc`. For a message the inbox sent, the reply goes to that message's `Reply-To` addresses when they are not the inbox address, otherwise to its `to` recipients, and copies its `cc` recipients. The inbox address is always excluded, and duplicates are removed. |
| `payload.attachments` | `array` | No | — | Files to attach, as on `POST /emails`. Each one needs `content` or `path`. The `content` of all files can total at most 25 MB. A `path` file does not count toward the 25 MB, because it is fetched when the email is sent. An empty file, a blocked file type, a `path` that does not start with `http` or that starts with `http://localhost:`, or a `content_type` that is not a valid MIME type returns a 422. Other `path` problems fail the email when it is sent, not the request. |
| `payload.headers` | `record` | No | — | Custom headers to add to the email. The `In-Reply-To`, `References` and `Reply-To` headers are set by Resend and cannot be set here. Sending one of them, in any letter case, returns a 422. Header names cannot be empty, and names and values cannot contain line breaks or null characters, or the request returns a 422. `null` means no custom headers. |
| `payload.idempotency_key` | `string` | No | — | Stable send identity for retries. Resend deduplicates for 24 hours. Plays derive a step key when omitted. Minimum length: 1. Maximum length: 256. |

<details>
  <summary>Show raw input schema</summary>

  ### Input JSON Schema

  ```json theme={"languages":{"custom":["/languages/deepline-prompt.json"]}}
  {
    "type": "object",
    "description": "At least one of `html` or `text` must contain more than whitespace.",
    "properties": {
      "inbox_id": {
        "type": "string",
        "description": "The Inbox ID or the inbox email address, such as `support@acme.com`. A value that contains `@` must be a valid email address, and any other value must be a UUID, or the request returns a 422. The address match is case-insensitive and never falls back to the inbox `name`. An address that matches no inbox returns a 404."
      },
      "thread_id": {
        "type": "string",
        "description": "The Thread ID.",
        "format": "uuid"
      },
      "email_id": {
        "type": "string",
        "description": "The Email ID of the message to reply to, as returned in `data[].id` by the list thread emails endpoint.",
        "format": "uuid"
      },
      "cc": {
        "description": "CC recipient email address. For multiple addresses, send as an array of strings. Without `reply_all`, the reply copies only these addresses. With `reply_all`, these addresses are merged with the copied recipients, without duplicates. `cc` and `bcc` combined must be fewer than 50 addresses. After the `to` recipients are added, the reply cannot exceed 50 recipients. Each address is `email@example.com` or `Name `. An address that is not valid returns a 422.",
        "anyOf": [
          {
            "type": "string"
          },
          {
            "type": "array",
            "maxItems": 49,
            "items": {
              "type": "string"
            }
          },
          {
            "type": "null"
          }
        ]
      },
      "bcc": {
        "description": "BCC recipient email address. For multiple addresses, send as an array of strings. BCC recipients of the original message are never copied. Each address is `email@example.com` or `Name `. An address that is not valid returns a 422.",
        "anyOf": [
          {
            "type": "string"
          },
          {
            "type": "array",
            "maxItems": 49,
            "items": {
              "type": "string"
            }
          },
          {
            "type": "null"
          }
        ]
      },
      "html": {
        "type": "string",
        "description": "The HTML body of the reply."
      },
      "text": {
        "type": "string",
        "description": "The plain-text body of the reply."
      },
      "subject": {
        "type": "string",
        "description": "The subject of the reply. Cannot be only whitespace or contain a line break. When omitted, the thread subject is used, prefixed with `Re:` if it does not already start with it.",
        "minLength": 1,
        "maxLength": 2000
      },
      "reply_all": {
        "type": "boolean",
        "description": "Reply to everyone on the original message. For a message the inbox received, the reply goes to its `Reply-To` addresses, or to its sender when it has none, and copies the other addresses of its `To` header and its `cc` recipients in `cc`. For a message the inbox sent, the reply goes to that message's `Reply-To` addresses when they are not the inbox address, otherwise to its `to` recipients, and copies its `cc` recipients. The inbox address is always excluded, and duplicates are removed.",
        "default": false
      },
      "attachments": {
        "type": [
          "array",
          "null"
        ],
        "description": "Files to attach, as on `POST /emails`. Each one needs `content` or `path`. The `content` of all files can total at most 25 MB. A `path` file does not count toward the 25 MB, because it is fetched when the email is sent. An empty file, a blocked file type, a `path` that does not start with `http` or that starts with `http://localhost:`, or a `content_type` that is not a valid MIME type returns a 422. Other `path` problems fail the email when it is sent, not the request.",
        "items": {
          "type": "object",
          "properties": {
            "content": {
              "type": "string",
              "description": "Content of an attached file.",
              "format": "binary"
            },
            "filename": {
              "type": "string",
              "description": "Name of attached file."
            },
            "path": {
              "type": "string",
              "description": "Path where the attachment file is hosted"
            },
            "content_type": {
              "type": "string",
              "description": "Optional content type for the attachment, if not set it will be derived from the filename property"
            },
            "content_id": {
              "type": "string",
              "description": "Content ID for embedding inline images using cid references (e.g., cid:image001)."
            }
          },
          "additionalProperties": false
        }
      },
      "headers": {
        "type": [
          "object",
          "null"
        ],
        "description": "Custom headers to add to the email. The `In-Reply-To`, `References` and `Reply-To` headers are set by Resend and cannot be set here. Sending one of them, in any letter case, returns a 422. Header names cannot be empty, and names and values cannot contain line breaks or null characters, or the request returns a 422. `null` means no custom headers.",
        "additionalProperties": {
          "type": "string"
        }
      },
      "idempotency_key": {
        "type": "string",
        "description": "Stable send identity for retries. Resend deduplicates for 24 hours; Plays derive a step key when omitted.",
        "minLength": 1,
        "maxLength": 256
      }
    },
    "required": [
      "inbox_id",
      "thread_id",
      "email_id"
    ],
    "additionalProperties": false
  }
  ```
</details>

## Output reference

Standard tool result payload.

| Name | Type | Required | Default | Details |
| - | - | - | - | - |
| `result.data` | `object` | Yes | — | Provider response payload. |
| `result.data.id` | `string` | Yes | — | The ID of the sent email. Use it with the emails endpoints. Format: `uuid`. |
| `result.meta` | `object` | No | — | Additional response metadata (status, paging). |

<details>
  <summary>Show raw output schema</summary>

  ### Output JSON Schema

  ```json theme={"languages":{"custom":["/languages/deepline-prompt.json"]}}
  {
    "type": "object",
    "description": "Standard tool result payload.",
    "properties": {
      "data": {
        "type": "object",
        "description": "Provider response payload.",
        "properties": {
          "id": {
            "type": "string",
            "description": "The ID of the sent email. Use it with the emails endpoints.",
            "format": "uuid"
          }
        },
        "required": [
          "id"
        ],
        "additionalProperties": false
      },
      "meta": {
        "type": "object",
        "description": "Additional response metadata (status, paging).",
        "additionalProperties": true
      }
    },
    "required": [
      "data"
    ],
    "additionalProperties": false
  }
  ```
</details>

## Deepline cost

* Pricing model: `fixed` (per call).
* Estimated Deepline credits: `0` per pricing unit.
* Provider-native pricing may still exist outside Deepline credit billing.

## Related documentation

* [Connect integrations](https://deepline.com/docs/integrations.md)
* [SDK V2 quickstart](https://deepline.com/docs/sdk-v2/quickstart.md)
* [SDK reference](https://deepline.com/docs/sdk-v2/sdk-reference.md)
* [Run tools across a CSV](https://deepline.com/docs/sdk-v2/batch-csv.md)


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