Sendmux Email Inbox Api + Sending

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-capablesmx_mbx_keys or owner-approved Sending-resourcesmx_agent_tokens for Sending clients. Usesmx_mbx_keys or scopedsmx_agent_tokens for Mailbox clients. Use rootsmx_root_*keys for Management clients. Agent tokens remain limited by server-side scopes; pre-claim self-registered agent tokens do not includeemail.send.

For command-line access, install the CLI:

brew install sendmux/tap/sendmux npm install -g @sendmux/cli sendmux --help

For MCP clients, installsendmux-mcpor connect to the hosted MCP endpoint:

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

The hosted MCP endpoint ishttps://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 fromhttps://a2a.sendmux.ai/.well-known/agent-card.json. It exposes the same curated mailbox, management, and sending operations with an OAuth grant bound specifically tohttps://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.

Mailbox attachment metadata now includes a short-liveddownload_url. Fetch that URL promptly with a plain HTTP client; it does not require anAuthorizationheader, 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.pdforsendmux sending:send --attach ./report.pdf.
- TypeScript: use@sendmux/mailbox/nodesendMailboxMessageWithFiles(...)or@sendmux/sending/nodesendEmailWithFiles(...).
- Python: usesendmux_mailbox.send_mailbox_message_with_files(...)orsendmux_sending.send_email_with_files(...).
- MCP: local stdio can usemailbox_upload_attachmentwithfile_path; hosted and shell-capable agents can mint a presigned upload URL,PUTbytes to it without an API key, then send with the returnedblob_id.

Mailbox direct uploads, presigned uploads, CLI--attach, and mailbox SDK file helpers share the mailbox attachment cap: currently7,500,000bytes 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 at32 KiBdecoded; the cheaper alternatives arefile_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 typedMailboxRealtimeEventmodels from the generated mailbox client.
- CLI:sendmux mailbox:stream-events --followprints one JSON event per line until the stream closes or the process is interrupted.
- MCP: usemailbox_wait_for_messagefor bounded waits inside agent tool calls, thenmailbox_get_attachmentto renew attachment metadata and fetchdownload_url.

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.

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

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