Sendmux

What It Does

Sendmux is a purpose-built email infrastructure platform designed specifically for AI agents. It provides a complete email stack—inbound mailboxes, outbound sending, intelligent routing, and real-time event streaming—unified under a single API surface. Unlike traditional email services that force you to stitch together separate sending and receiving providers, Sendmux delivers agent-shaped inboxes that return clean, structured JSON instead of token-heavy HTML, dramatically reducing LLM compute waste.

Who It's For

Sendmux is built for AI agent developers, automation engineers, and teams building autonomous systems that need to interact with the world via email. Whether you're building customer support agents, sales assistants, invoice processors, or any agent that needs to send and receive messages, Sendmux handles the email layer so you can focus on agent logic.

Key Features & Capabilities

• Agent Inboxes: Create dedicated mailboxes on verified custom domains or shared @myagent.mx addresses with automatic signature and quote stripping, link extraction, and attachment metadata handling
• Token-Efficient JSON: Receive messages as clean, structured JSON that consumes 96% fewer tokens than raw MIME (127 tokens vs. 3,247), saving compute and cost
• Provider-Agnostic Sending: Send via HTTP or SMTP through your own providers with idempotency support, text/HTML bodies, custom headers, and up to 10 attachments per message
• Intelligent Routing: Configure quota-based, weighted delivery across multiple providers with failover, delivery groups, and per-second/minute/hour/day limits
• Real-Time Events: React to incoming mail, delivery confirmations, spam reports, and bounces via signed webhooks, server-sent events (SSE), or typed change polling—no polling loops required
• Multi-Agent Management: Unified inbox dashboard for monitoring every agent mailbox from one keyboard-driven interface with bulk actions, labels, threads, and cross-inbox search
• Native AI Integrations: Official SDKs for TypeScript, Python, LangChain, and AI SDK; MCP server for Claude Code; CLI tools; and OpenClaw skills for instant agent onboarding

Typical Workflows

Developers create mailboxes via the Management API, grant scoped credentials to agents, then stream incoming messages over SSE or webhooks. Agents parse the clean JSON, make decisions, and reply via the same credential used as both Bearer token and SMTP password. Routing rules ensure messages go out through the right provider pool, respecting quotas and weights. The unified inbox lets human operators monitor, intervene, or take over threads when needed.

Integrations & Extensibility

Sendmux integrates natively with major AI frameworks (LangChain, AI SDK), platforms (Claude via MCP), and automation tools (Zapier). The REST API, webhooks, and SDKs support custom workflows, while the CLI and MCP server enable rapid prototyping and agent skill installation. SMTP compatibility ensures legacy system support.

What Differentiates It

Unlike Gmail, Outlook, or traditional ESPs, Sendmux returns agent-optimized JSON that strips noise and preserves only actionable content. Unlike sending-only services, it provides full inbound capabilities. Unlike inbox-only providers, it handles outbound routing with multi-provider flexibility. The result is one platform, one bill, one API—purpose-built for agents, not humans.