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@v1.0.0
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 --help

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.

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 pack