Sendmux SDKs

Official SDK, CLI, and MCP workspace for Sendmux.

• Product documentation: sendmux.ai/docs
• Management API reference: sendmux.ai/docs/api/introduction
• Mailbox API reference: sendmux.ai/docs/mailbox-api/introduction
• Sending API reference: sendmux.ai/docs/sending-api/introduction
• MCP guide: sendmux.ai/docs/guides/mcp

Packages

Quick start

Install only the package for the surface you need.

npm install @sendmux/sending
pip install sendmux-sending
go get sendmux.ai/go@v1.4.1
cargo add sendmux
composer require sendmux/sending:^1.0
gem install sendmux-sending

Use send-capable `smx_mbx_*` keys or owner-approved Sending-resource `smx_agent_*` tokens for Sending clients. Use `smx_mbx_*` keys or scoped `smx_agent_*` tokens for Mailbox clients. Use root `smx_root_*` keys for Management clients. Agent tokens remain limited by server-side scopes; pre-claim self-registered agent tokens do not include `email.send`.

For command-line access, install the CLI:

brew install sendmux/tap/sendmux
npm install -g @sendmux/cli
sendmux agent:register my-agent --mailbox-local-part my-agent --default --json

Agent registration does not require an existing account or API key. It creates a local profile with a durable, revocable credential for reading and receiving mail. To send, invite the owner with `sendmux agent:invite-owner owner@example.com --profile my-agent`; after the owner accepts and approves sending, Sending API commands exchange and cache a one-hour delegated token automatically.

For MCP clients, install `sendmux-mcp` or connect to the hosted MCP endpoint:

pip install sendmux-mcp
sendmux-mcp-mailbox --help

The hosted MCP endpoint is `https://mcp.sendmux.ai/mcp`. Local MCP commands support stdio and HTTP transports; hosted MCP uses OAuth and does not require manual API keys or custom OAuth endpoints.

For A2A 1.0 clients, discover the hosted HTTP+JSON service from `https://a2a.sendmux.ai/.well-known/agent-card.json`. It exposes the same curated mailbox, management, and sending operations with an OAuth grant bound specifically to `https://a2a.sendmux.ai/a2a/v1`.

For AI-agent frameworks, first-party tool wrappers are available:

npm install @sendmux/ai-sdk ai zod   # Vercel AI SDK: sendmux({ apiKey }) returns a ToolSet
pip install langchain-sendmux        # LangChain: SendmuxToolkit(api_key=...).get_tools()

Both wrap the generated Sending and Mailbox clients, so the OpenAPI spec stays the single source of truth.

Attachments And Live Mailbox Events

Mailbox attachment metadata now includes a short-lived `download_url`. Fetch that URL promptly with a plain HTTP client; it does not require an `Authorization` header, but it expires after a short TTL. If a download URL expires, re-fetch the message or attachment metadata to receive a fresh URL.

For outbound files, avoid manually placing base64 in prompts or source strings. Use the zero-context path for your lane:

• CLI: `sendmux mailbox:send-message --attach ./report.pdf` or `sendmux sending:send --attach ./report.pdf`.
• TypeScript: use `@sendmux/mailbox/node` `sendMailboxMessageWithFiles(...)` or `@sendmux/sending/node` `sendEmailWithFiles(...)`.
• Python: use `sendmux_mailbox.send_mailbox_message_with_files(...)` or `sendmux_sending.send_email_with_files(...)`.
• MCP: local stdio can use `mailbox_upload_attachment` with `file_path`; hosted and shell-capable agents can mint a presigned upload URL, `PUT` bytes to it without an API key, then send with the returned `blob_id`.

Mailbox direct uploads, presigned uploads, CLI `--attach`, and mailbox SDK file helpers share the mailbox attachment cap: currently `7,500,000` bytes per attachment. Sending API attachment helpers encode files into the send request body; the generated Sending API limit is max 10 attachments and a 25 MB request body.

Small generated attachments can still use inline base64 where the API schema supports them. MCP inline base64 is capped at `32 KiB` decoded; the cheaper alternatives are `file_path`, presigned upload, CLI `--attach`, and SDK file helpers.

Live mailbox events are available through idiomatic lanes:

• TypeScript: `streamMailboxEvents(...)` returns an async iterator over typed mailbox realtime events.
• Python: `iter_mailbox_events(...)` yields typed `MailboxRealtimeEvent` models from the generated mailbox client.
• CLI: `sendmux mailbox:stream-events --follow` prints one JSON event per line until the stream closes or the process is interrupted.
• MCP: use `mailbox_wait_for_message` for bounded waits inside agent tool calls, then `mailbox_get_attachment` to renew attachment metadata and fetch `download_url`.

Repository structure

Versioning and support

SDK packages track the Sendmux public API contracts. Patch versions can differ between packages when a fix only affects one ecosystem or runtime.

Generated clients are built from committed OpenAPI snapshots. Any API contract change must update the snapshots and generated output in the same change.

For help, open a GitHub issue with the package name, version, command or import path, and the request ID from any API error response.

Contributing

Open pull requests against this repository. Keep generated output, source snapshots, and verification artefacts together in the same change.

Security issues should be reported through GitHub Security Advisories.

Licence

This repository is available under the MIT licence.