# 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, documentation, Sending API OpenAPI spec, Management API OpenAPI spec, SDKs, CLI, Doc Search MCP, MCP, and A2A. ## 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/): Free includes two mailboxes and 50 accepted recipients a day across all outbound routes. Pro is $7 per team each month, plus per-event usage. - [Free email tools](https://sendmux.ai/tools/): Browser-based tools for debugging email after the fact, starting with a header analyzer. No account needed. - [Email header analyzer](https://sendmux.ai/tools/email-header-analyzer/): Paste a raw header block to trace the delivery path in delivery order, the delay at every hop, ARC forwarding chains, and the SPF, DKIM and DMARC results the receiving server recorded. Parses entirely in the browser; nothing is uploaded. - [Blog](https://sendmux.ai/blog/): Technical guides for sending, receiving, authentication, deliverability, and agent email infrastructure. - [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 Pro team per customer, mailbox-scoped API keys, signed webhooks, and 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 agents, provisioned by agents](https://sendmux.ai/solutions/for-ai-agents/): Agent-facing landing for agents with no credential to start. `sendmux agent:register ` creates an @myagent.mx inbox with a durable read credential that does not expire and a 500 MiB storage limit. `sendmux agent:invite-owner owner@example.com --profile ` invites the owner. Owner acceptance and sending approval guarantee at least 5 GiB of inbox storage before sending uses a one-hour delegated token. Revoking sending does not itself change the current inbox storage allocation. - [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. - [Email for AI monitoring agents](https://sendmux.ai/use-cases/monitoring-agents/): Use-case page for AI monitoring agents: a dedicated mailbox that catches every inbound alert over a signed webhook or a live event stream, de-dupes repeat events for 24 hours, filters trusted senders with allowlist rules, reads each alert as clean content, and escalates with an idempotent send so a retried page fires once. Sendmux is the email rail; the agent's own model classifies and decides who to page. ## 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, Ruby, and Rust SDKs for Sending, Mailbox, and Management APIs. - [CLI](https://sendmux.ai/docs/cli): Install `@sendmux/cli` to register agent inboxes, invite owners, and run 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 CLI-first agent registration, durable inbox reads, owner invitations, one-hour delegated sending after approval, HTTP fallback, and full 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. - [Agent email inbox](https://sendmux.ai/.well-known/agent-skills/agent-email-inbox/SKILL.md): Inbox triage and unsent replies. - [Email for AI agents](https://sendmux.ai/.well-known/agent-skills/email-for-ai-agents/SKILL.md): Approved sends and idempotent retries. - [A2A Agent Card](https://sendmux.ai/.well-known/agent-card.json): A2A 1.0 discovery metadata for deterministic, OAuth-authorised Sendmux mailbox, management, and sending operations. - [API catalog](https://sendmux.ai/.well-known/api-catalog): Linkset JSON catalog of Sendmux API endpoints, docs, and OpenAPI specs. - [MCP discovery](https://sendmux.ai/.well-known/mcp.json): Sendmux's hosted MCP endpoint. - [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 - Free: $0 per month, two mailboxes, $1 usage credit, fixed limits, and 50 provider-accepted recipients per UTC day across all outbound routes. Usage draws from the credit. Free credit cannot be topped up. Upgrade to Pro for more capacity. Messages add the plain text "Email sent via Sendmux" after supported message bodies. - Pro: $7 per team each month, plus usage, with Unlimited* resource capacity. Fair usage applies, and resource increases require admin approval. - Outgoing mail through customer-owned or connected providers: $0.000500 per provider-accepted recipient occurrence. - Accepted inbound mail: $0.000500 per distinct mailbox delivery. - Managed sending: $0.000750 per provider-accepted recipient occurrence. - Each provider-accepted To, CC, or BCC recipient occurrence is billed. Addresses rejected before provider acceptance are not charged. - Mailbox storage: $0.02 per decimal GB-month. - Each usage event is billed individually, not in blocks of 1,000. There are no per-seat or per-mailbox fees. ## Current product notes - Use managed sending for triggered and transactional email. Free is capped at two accepted recipients per hour and shares a 50-recipient UTC daily cap across all outbound routes. Pro has no Sendmux speed cap and keeps the team's current daily allowance, including approved increases, while Amazon SES account and regional sending limits still apply. On Pro and Enterprise, Sendmux adds no sending caps to customer-owned providers, but provider limits still apply to each connected account. Customer-configured quotas still apply. Marketing, newsletters, sales outreach, and bulk promotional campaigns should use a customer-owned provider. - Documentation MCP, product MCP, A2A, SDKs, CLI, and Agent Skills are live developer surfaces. Install skills with `npx skills add Sendmux/skills`. Product MCP and A2A expose authorised Management, Mailbox, and Sending operations; SDKs cover TypeScript, Python, Go, PHP, Ruby, and Rust; the CLI is `@sendmux/cli` with the `sendmux` command. - Agent API access starts with `sendmux agent:register `, which creates a private profile containing a durable `smx_agent_` read credential. The credential includes `mailbox.read` and `email.receive`, does not expire, cannot send, and starts with a 500 MiB storage limit. Use `sendmux agent:invite-owner owner@example.com --profile ` to invite the owner. Owner acceptance and explicit sending approval guarantee at least 5 GiB of inbox storage before Sending commands exchange the durable credential for a one-hour `email.send` token. Revoking sending does not itself change the current inbox storage allocation. The HTTP fallback and full-revocation flow are documented at `https://sendmux.ai/auth.md`. - 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.