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

# Ruby SDK

> Install and configure the Sendmux Ruby SDK gems.

Use the Ruby SDK when your application needs gems for the Sending, Mailbox, or Management API.

<Info>
  Sending clients accept a send-capable `smx_mbx_` key or owner-approved Sending-resource `smx_agent_` token. Mailbox clients accept
  `smx_mbx_` keys or scoped `smx_agent_` tokens. Management clients require
  team-scoped `smx_root_` keys.
</Info>

## Requirements

* Ruby 3.1 or newer.
* A Sendmux API key for the surface you are calling.

## Install

Install the umbrella gem when one application needs more than one API surface.

<CodeGroup>
  ```bash Umbrella theme={null}
  gem install sendmux-sdk
  ```

  ```bash Sending theme={null}
  gem install sendmux-sending
  ```

  ```bash Mailbox theme={null}
  gem install sendmux-mailbox
  ```

  ```bash Management theme={null}
  gem install sendmux-management
  ```
</CodeGroup>

## Create a client

The umbrella gem exposes helpers for each surface.

<CodeGroup>
  ```ruby Sending theme={null}
  require 'sendmux/sdk'

  client = Sendmux::SDK.sending(
    api_key: ENV.fetch('SENDMUX_MAILBOX_API_KEY')
  )
  ```

  ```ruby Mailbox theme={null}
  require 'sendmux/sdk'

  client = Sendmux::SDK.mailbox(
    api_key: ENV.fetch('SENDMUX_MAILBOX_API_KEY')
  )
  ```

  ```ruby Management theme={null}
  require 'sendmux/sdk'

  client = Sendmux::SDK.management(
    api_key: ENV.fetch('SENDMUX_ROOT_API_KEY')
  )
  ```
</CodeGroup>

Surface gems expose `Sendmux::Sending::Client`, `Sendmux::Mailbox::Client`, and `Sendmux::Management::Client` directly.

## Choose a surface

| Surface    | Gem                  | Client or helper                              | API key                                                     |
| ---------- | -------------------- | --------------------------------------------- | ----------------------------------------------------------- |
| Sending    | `sendmux-sending`    | `Sendmux::SDK.sending`, `client.emails`       | `smx_mbx_` or owner-approved `smx_agent_` with `email.send` |
| Mailbox    | `sendmux-mailbox`    | `Sendmux::SDK.mailbox`, `client.mailbox_api`  | `smx_mbx_` or scoped `smx_agent_`                           |
| Management | `sendmux-management` | `Sendmux::SDK.management`, `client.mailboxes` | `smx_root_`                                                 |

<Note>
  Pre-claim `smx_agent_` tokens are mailbox-compatible only. Owner-approved Sending-resource `smx_agent_` tokens can send. Pre-claim self-registered agent tokens include `mailbox.read` and `email.receive`, not `email.send`.
</Note>

Sending uses `https://smtp.sendmux.ai/api/v1` by default. Mailbox and Management use `https://app.sendmux.ai/api/v1`.

## Shared API behaviour

Surface clients validate API key prefixes, configure bearer auth, and map generated API errors.

### Pagination

List responses use cursor pagination with `pagination.has_more` and `pagination.next_cursor`. The core gem exports `Sendmux::Core.each_cursor()` and `Sendmux::Core::CursorPager` for cursor iteration when you wrap a page-fetching function.

### Retries and rate limits

Surface clients call `Sendmux::Core::Retry.configure()` by default. Retries apply to safe methods and retry-safe `POST` requests that include `Idempotency-Key`, then honour `Retry-After` and `X-RateLimit-Reset` response headers.

Pass `Sendmux::Core::RetryOptions` into a surface helper or client to change attempts, delays, or jitter.

### Idempotency and ETags

Use core header helpers when a generated operation accepts custom headers.

```ruby theme={null}
headers = Sendmux::Core::Headers.conditional(if_match: etag)
headers.merge!(Sendmux::Core::Headers.idempotency_key('order-123'))
```

Use `Idempotency-Key` for retry-safe mutating requests. Use `If-Match` and `If-None-Match` with single-resource endpoints that support ETags.

### Errors

Generated API errors are mapped to `Sendmux::Core::ApiError`. The error includes status, code, retryability, request ID, param, nested errors, response body, and response headers when available.

Use the request ID when contacting support.

## Next steps

<CardGroup cols={2}>
  <Card title="SDK overview" icon="code" href="/docs/sdks">
    Choose the right package family and API surface.
  </Card>

  <Card title="Versioning and support" icon="rotate" href="/docs/sdks/versioning-support">
    Check compatibility, support, and upgrade guidance.
  </Card>

  <Card title="Sending API" icon="paper-plane" href="/docs/sending-api/introduction">
    Review the Sending API contract used by `sendmux-sending`.
  </Card>

  <Card title="API keys" icon="key" href="/docs/guides/api-keys">
    Create and scope the credentials used by SDK clients.
  </Card>
</CardGroup>