# Sendmux

> Sendmux is the email API for AI agents and SaaS platforms. It combines multi-provider outbound sending, agent inboxes, scoped APIs, webhooks, live mailbox events, and usage-based billing.

Sendmux is built for teams that need agents to send, receive, route, and process email without stitching together a sending provider, a mailbox provider, parsing code, webhook delivery, separate credentials, and separate billing. Current public surfaces include the marketing site, Mintlify documentation, Sending API OpenAPI spec, Management API OpenAPI spec, SDKs, CLI, Doc Search MCP, and MCP.

## Website

- [Homepage](https://sendmux.ai/): Product overview for the email API for AI agents.
- [Product overview](https://sendmux.ai/product): Hub for sending, inbound mailboxes, and platform controls.
- [Sending API and SMTP relay](https://sendmux.ai/product/sending): Multi-provider outbound routing, delivery groups, quotas, health checks, failover, HTTP sending, SMTP submission, and idempotency.
- [Agent inbox API](https://sendmux.ai/product/inboxes): Dedicated mailboxes for agents with REST, IMAP, SMTP submission, clean content endpoints, attachments, sender rules, webhooks, and Server-Sent Events.
- [Platform API controls](https://sendmux.ai/product/platform): Team isolation, scoped API keys, signed webhooks, Server-Sent Events, logs, usage controls, and code examples.
- [Pricing](https://sendmux.ai/pricing): Usage-based pricing with no per-seat or per-mailbox fees.
- [Contact](https://sendmux.ai/contact): Sales and support contact paths.
- [Email API for AI agent builders](https://sendmux.ai/solutions/ai-agent-builders): Audience landing for AI agent builders: real agent mailboxes, authorised sending via MCP and the Sending API, clean reply content, and live mailbox events.
- [Email API for multi-tenant SaaS platforms](https://sendmux.ai/solutions/platform-builders): Audience landing for SaaS and platform builders: one isolated team per customer, mailbox-scoped API keys, signed webhooks and live events, and usage-based billing with no per-mailbox fees.
- [Enterprise email API for AI agent fleets](https://sendmux.ai/solutions/enterprise): Sales-led landing for organisations running fleets of AI agents: isolated teams, role-based access, scoped credentials, SHA-256 hashed keys and HMAC-SHA256 signed webhooks, and load-tested scale. Dedicated infrastructure, custom SLAs, priority support, and a security review come by enterprise agreement; SSO/SAML and compliance certifications are on the roadmap.
- [Email for AI customer support agents](https://sendmux.ai/use-cases/customer-support-agents): Use-case page for AI customer support agents: a dedicated mailbox that receives customer email, reads it as clean JSON with quoted history and signatures stripped, replies from the same address, and applies keyword labels over REST or MCP, with sender rules and usage-based pricing.
- [Email API for AI sales outreach agents](https://sendmux.ai/use-cases/sales-outreach-agents): Use-case page for AI sales outreach agents: route outbound through your own providers with per-provider quotas, weighted distribution, and failover so sending reputation stays on your own identities, then catch every reply in the agent's mailbox, thread it, read it clean, and label intent over REST or MCP. Sendmux is the send-and-reply layer; no warmup, sequencing, or campaign builder.
- [Email for AI scheduling agents](https://sendmux.ai/use-cases/scheduling-agents): Use-case page for AI scheduling agents: a dedicated mailbox that catches the booking request, reads the proposed times as clean JSON with the booking link extracted, threads the whole negotiation, confirms with an agent-built .ics, coordinates several attendees, and reminds or reschedules over REST or MCP. Sendmux is the email layer; the agent and its own calendar do the scheduling.

## Developer reference

- [Sendmux documentation](https://sendmux.ai/docs): Guides and API references.
- [Quickstart](https://sendmux.ai/docs/guides/quickstart): Create a team, add a mailbox, send a test email, and check logs.
- [Sending API reference](https://sendmux.ai/docs/sending-api/introduction): HTTP sending API reference.
- [Management API reference](https://sendmux.ai/docs/api/introduction): Team, provider, domain, mailbox, webhook, billing, log, and metric API reference.
- [Mailbox API reference](https://sendmux.ai/docs/mailbox-api/introduction): Mailbox-scoped API reference for agent mailboxes.
- [Send by HTTP](https://sendmux.ai/docs/guides/sending-via-http): Queue single or batch email requests.
- [Send via SMTP](https://sendmux.ai/docs/guides/sending-via-smtp): SMTP submission guide for existing clients and agent frameworks.
- [Webhooks](https://sendmux.ai/docs/guides/webhooks-setup): Subscribe to delivery and mailbox events.
- [Verify webhook signatures](https://sendmux.ai/docs/guides/webhooks-verify-signatures): Verify HMAC-SHA256 webhook deliveries.
- [Idempotency](https://sendmux.ai/docs/guides/idempotency): Retry mutating requests without duplicate sends.
- [SDKs](https://sendmux.ai/docs/sdks): Package-managed TypeScript, Python, Go, PHP, and Ruby SDKs for Sending, Mailbox, and Management APIs.
- [CLI](https://sendmux.ai/docs/cli): Install `@sendmux/cli` and use the `sendmux` command for Management, Mailbox, and Sending workflows.
- [MCP servers](https://sendmux.ai/docs/guides/mcp): Connect AI tools to the documentation MCP for docs search or the product MCP for authorised Sendmux tools.
- [Agent access service document](https://sendmux.ai/auth.md): Machine-readable entry point for API protected-resource discovery, optional `npx skills add Sendmux/skills` install, anonymous agent identity registration, secure agent credential-bundle storage, pre-claim owner invite, post-approval token exchange, and revocation.
- [Agent Skills guide](https://sendmux.ai/docs/guides/agent-skills): Install the full Sendmux skill pack with `npx skills add Sendmux/skills`, or install focused Sendmux skills.
- [Agent skills](https://sendmux.ai/.well-known/agent-skills/sendmux-getting-started/SKILL.md): Official Sendmux agent skills for setup, auth, agent access, sending, mailbox, management, MCP, and CLI. Install the pack with `npx skills add Sendmux/skills`; the full set is indexed at https://sendmux.ai/.well-known/agent-skills/index.json.
- [API catalog](https://sendmux.ai/.well-known/api-catalog): Linkset JSON catalog of Sendmux API endpoints, docs, and OpenAPI specs.
- [Web Bot Auth key directory](https://sendmux.ai/.well-known/http-message-signatures-directory): JWKS for verifying signed Sendmux bot and agent requests.
- [Sending API OpenAPI 3.1 spec](https://smtp.sendmux.ai/api/v1/openapi.json): Machine-readable spec for sending endpoints.
- [Management API OpenAPI 3.1 spec](https://app.sendmux.ai/api/v1/openapi.json): Machine-readable spec for management and mailbox endpoints.

## Pricing

- Standard outgoing mail through customer-owned providers: $0.15 per 1,000 emails.
- Accepted inbound mail: $0.15 per 1,000 emails.
- Outgoing mail through the managed Amazon SES route: $0.25 per 1,000 emails.
- Mailbox storage: $0.02 per GB per month.
- No per-seat fees, no per-mailbox fees, and no minimum commitments in the standard usage-based model.

## Current product notes

- The managed Amazon SES route is intended for triggered and transactional email. Marketing, newsletters, sales outreach, and bulk promotional campaigns should use a customer-owned provider.
- Documentation MCP, product MCP, SDKs, CLI, and Agent Skills are live developer surfaces. Install skills with `npx skills add Sendmux/skills`. Product MCP exposes authorised Management, Mailbox, and Sending tools; SDKs cover TypeScript, Python, Go, PHP, and Ruby; the CLI is `@sendmux/cli` with the `sendmux` command.
- Agent API access starts from `https://sendmux.ai/auth.md` or an unauthenticated API `401` with `WWW-Authenticate` resource metadata. Self-registered `smx_agent_` tokens are mailbox-only and include `mailbox.read` plus `email.receive`, not `email.send`. Agents must immediately save the returned `claim_token` and full agent credential bundle before token exchange: mailbox metadata, token endpoints, resource URLs, and `identity_assertion`; keep `identity_assertion` or the pre-claim token until the owner invite returns `202`. `claim_token` is only for post-approval exchange.
- WebSockets are roadmap. The live mailbox event stream is Server-Sent Events.

## Optional

- [Changelog](https://sendmux.ai/docs/changelog): Product updates and release notes.
- [Acceptable use](https://sendmux.ai/acceptable-use): Policy for allowed and disallowed use.
- [Privacy](https://sendmux.ai/privacy): Privacy policy.
- [Terms](https://sendmux.ai/terms): Service terms.
- [Data Processing Agreement](https://sendmux.ai/dpa): Data processing terms.