# create

URL: /business/nouns/mailbox/create · Id: `verb:Mailbox.create` · Call: `await $.Mailbox.create({ … })` (SDK) or the `do` tool at `https://api.sb/mcp`. Inputs says what to pass, Outputs what returns, When it waits who approves.

> Creates a Mailbox.

Create makes a new [Mailbox](/business/nouns/mailbox) from the inputs below. It is inherited: every [Noun](/business/nouns/noun) has `get`, `list`, `create`, `update` and `delete`.

## Inputs
| Input | Type | Required | Description |
| --- | --- | --- | --- |
| `medium` | `string` | Yes | The platform type, such as `email`, `sms`, or `chat`. |
| `organization` | [Organization](/business/nouns/organization) | No | The outside Organization the Channel is shared with; its new Messages open Conversations for that Customer. |
| `external` | `boolean` | No | True when people from another Organization post in it, as in a channel two companies share. |
| `areaCode` | `string` | No | For an `sms` Channel, the phone area code its number is drawn from, such as `512`. |
| `number` | `string` | No | For an `sms` Channel, its phone number in international form, assigned when it is created. |
| `address` | `email` | Yes | The email address. |
| `stream` | `string` | Yes | What it sends: receipts and resets, broadcasts, or cold outbound; one stream per Mailbox. |
| `tenant` | [Tenant](/business/nouns/tenant) | No | The Tenant it sends for, at a Domain that Tenant’s Customer holds; replies land in the Tenant’s Threads. |

## Outputs
| Output | Type | Required | Description |
| --- | --- | --- | --- |
| `mailbox` | [Mailbox](/business/nouns/mailbox) | Yes | The Mailbox. |

## Effects
- Emits `Mailbox.created`.
- Two-way: `try`, `send`, `do`.

## Refuses when
| Check | Error | Fix | Then call |
| --- | --- | --- | --- |
| The key is valid, but its scopes do not allow this operation. | [`forbidden`](/code/api/errors/forbidden) | Use a key whose scopes cover the operation, or ask an owner of the namespace to grant them. | [Mailbox.create](/business/nouns/mailbox/create) |

## When it waits
| Gate | Default |
| --- | --- |
| Decision class | Low: two-way, nothing at stake |
| [Delay window](/systems/trust-and-governance/controls/one-way-windows) | None: it runs once review passes. |
| Limit | The call [Limit](/business/nouns/limit) of the [Permission](/business/nouns/permission) it runs under. |
| Over the Limit | It waits `pending` for an [Approval](/business/nouns/approval) from the [Founder](/agents/founding/founder). Approved, it runs; refused, it ends `refused` with [`limit-exceeded`](/code/api/errors/limit-exceeded); unanswered by its deadline, it ends `canceled`. |

## Example

**Ask**

```text
Add a mailbox to QuietCopy.
```

**API**

```bash
curl -X POST https://api.sb/quietcopy.com/mailboxes \
  -H "Authorization: Bearer $STARTUP_BUILDER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"medium":"email","address":"mei@quietcopy.com","stream":"transactional"}'
```

```json
{
  "api": "https://api.sb/quietcopy.com",
  "mailbox": {
    "$id": "https://api.sb/quietcopy.com/mailboxes/mailbox_1",
    "$type": "Mailbox",
    "medium": "email",
    "address": "mei@quietcopy.com",
    "stream": "transactional"
  },
  "action": {
    "$id": "https://api.sb/quietcopy.com/actions/action_1",
    "operation": "Mailbox.create",
    "status": "done"
  },
  "links": {
    "self": "https://api.sb/quietcopy.com/actions/action_1"
  }
}
```

**SDK**

```ts
import { $ } from 'startup-builder'

const mailbox = await $.Mailbox.create({ medium: 'email', address: 'mei@quietcopy.com', stream: 'transactional' })
```

**CLI**

```bash
npx startup-builder do Mailbox.create --json '{"medium":"email","address":"mei@quietcopy.com","stream":"transactional"}'
```

**MCP**

```json
{
  "name": "do",
  "arguments": {
    "code": "return await $.Mailbox.create({ medium: 'email', address: 'mei@quietcopy.com', stream: 'transactional' })"
  }
}
```

Guides that call it: [Get email at my domain](/products/site/domains/get-email-at-my-domain).