Sendmux

What is Sendmux

Sendmux is an email API designed specifically for AI agents and SaaS platforms. It provides dedicated mailboxes, multi-provider outbound sending, live inbox events, and developer tools so agents can send, receive, route, and react to email in production. It combines outbound sending, agent inboxes, routing controls, and delivery events into one API surface.

How to use Sendmux

1. Create an agent inbox – Sign up at app.sendmux.ai and create a mailbox on a verified custom domain or the shared myagent.mx domain.
2. Connect your email providers – Add SMTP, Gmail, Microsoft 365, or Amazon SES sending accounts. You can also use the built-in managed Amazon SES route (capped at 50 emails/day for testing).
3. Configure routing – Set up delivery groups with weights, quotas, and sender-domain routing. Sendmux automatically skips unhealthy providers.
4. Send and receive via API – Use the Mailbox API to send messages, read inbox content as clean JSON, reply to threads, and stream events via Server-Sent Events or webhooks.
5. Monitor and manage – Use the unified inbox dashboard to view all agent inboxes, search across them, and perform bulk actions.

Features of Sendmux

• Agent-shaped inboxes – Dedicated mailboxes on custom domains or myagent.mx. Receive email as clean JSON with signatures, quoted history, and HTML stripped by default.
• Multi-provider outbound sending – Connect your own SMTP, Gmail, Microsoft 365, or Amazon SES accounts. Send via HTTP or SMTP with idempotency support.
• Intelligent routing – Weighted distribution across providers with automatic failover. Quotas at per-second, minute, hour, and day levels.
• Live events – Signed webhooks for server delivery, Server-Sent Events for live mailbox clients, and typed change polling for resync.
• Unified inbox dashboard – View all agent inboxes in one place, search across them, use keyboard shortcuts, and perform bulk actions (archive, label, spam, delete).
• Developer tools – SDKs for TypeScript, Python, Go, PHP, and Ruby; a CLI tool; MCP servers for doc search and authorized management.
• Clean content extraction – Return message bodies with signatures and quoted history stripped, or include links, headers, and attachment metadata on request.
• Mailbox API – Exposes messages, threads, folders, identities, usage, quotas, submissions, and clean message content.

Use Cases of Sendmux

• AI agents – Give each agent its own inbox to send, receive, reply, and read threads programmatically without a human webmail session.
• SaaS platforms – Provide email capabilities to your users with multi-provider routing, failover, and usage-based billing.
• Automated customer support – Agents can handle inbound support tickets, reply with structured data, and escalate to humans when needed.
• Transactional email – Send receipts, notifications, and alerts through your own providers with automatic failover.
• Email parsing and processing – Extract clean text from emails for LLM processing, reducing token consumption by up to 96% compared to raw HTML.

Pricing

• Standard emails – $0.15 per 1,000 outgoing or accepted inbound emails.
• Managed Amazon SES route – $0.25 per 1,000 emails.
• Mailbox storage – $0.02 per GB per month.
• No per-seat or per-mailbox fees. Free to start with a daily cap on the managed route.

FAQ

What is Sendmux? Sendmux is the email API for AI agents and SaaS platforms. It combines multi-provider outbound sending, agent inboxes, dedicated inbound mailboxes, team-scoped controls, webhooks, Server-Sent Events, and usage-based billing.

What can an AI agent do with Sendmux? An agent can send, receive, reply, read threads, stream new mailbox events, download attachments, and use scoped credentials tied to one mailbox.

Can I use my own SMTP or email provider? Yes. Connect SMTP, Gmail, Microsoft 365, or Amazon SES sending accounts. Delivery groups let you set weights, quotas, and sender-domain routing.

Does Sendmux include inbound mailboxes? Yes. Create mailboxes on myagent.mx or verified custom domains. Each mailbox can receive mail, send mail, hold messages, expose mailbox-scoped credentials, set sender rules, and stream events.

How does Sendmux help with email parsing? Mailbox content endpoints can return cleaned message content for agent processing, with controls for signatures, quoted history, links, and body output.

What are Sendmux webhooks and Server-Sent Events for? Use webhooks when your backend should receive signed event POSTs even when an agent is offline. Use SSE when an agent keeps an HTTP connection open and reacts as soon as a mailbox event arrives.

How does Sendmux pricing work? Usage-based pricing: $0.15 per 1,000 standard outgoing or accepted inbound emails, $0.25 per 1,000 emails through the managed Amazon SES route, and $0.02 per GB of mailbox storage per month. No per-seat or per-mailbox fees.

Can I send without setting up my own provider? Yes. Every team starts with a managed Amazon SES route, capped at 50 emails a day, for triggered and transactional mail.

Does Sendmux have an MCP server or SDKs? Yes. Sendmux has a Doc Search MCP, an MCP for authorised Management/Mailbox/Sending tools, SDKs for TypeScript, Python, Go, PHP, and Ruby, and the @sendmux/cli command-line tool.

Is Sendmux for human inboxes? Sendmux is for software teams and agents, not personal webmail. Human users can manage teams and settings in the dashboard, but the product is built around APIs, scoped keys, mailbox events, routing, and billing controls for automated workflows.