Sendmux

About Sendmux

Sendmux is an email API built specifically for AI agents, which in practice means it solves the receiving half that transactional email providers largely ignore. You create a real mailbox for an agent, then send through your own providers and receive over server-sent events rather than polling — the SDK exposes a `streamMailboxEvents` async iterator that yields `message.received` events as they arrive. The routing layer is the other half: quotas, weighted delivery across multiple providers, and failover, configured through one API instead of per-provider glue. Integration surface is deliberately broad for agent stacks. There is a hosted MCP endpoint at mcp.sendmux.ai with OAuth and scoped grants, an installable skills package via `npx skills add Sendmux/skills`, a global CLI (`@sendmux/cli`) with a `mailbox:stream-events --follow` command that emits one JSON object per line, TypeScript and Python SDKs, a LangChain toolkit exposing send_email, list_messages, and reply as agent tools, and a Vercel AI SDK adapter. The site publishes an llms.txt and an auth.md written for agents to read and self-onboard from. Idempotency keys are supported on sends. Usage is metered per email with a live dashboard showing sends and spend, and the vendor is explicit that seats, mailboxes, and tiers are not metered — only volume is.

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