Sendmux

Sendmux is an email inbox API for AI agents that lets developers give agents real mailboxes, controlled outbound sending, live inbox events, and developer tools in one platform. Instead of stitching together a sending API, mailbox provider, parser, webhook service, and separate billing system, teams can use Sendmux as the email API layer for agents that need to send, receive, route, and react to email in production.

Sendmux supports dedicated agent mailboxes on the included myagent.mx domain or verified custom domains. Agents can read messages, threads, folders, attachments, identities, usage, quotas, submissions, and mailbox metadata through the Mailbox API. They can also send, reply, reply-all, and forward from a mailbox, with clean extracted content available so agents can process new replies without parsing raw email manually.

For outbound email, Sendmux supports SMTP providers, Gmail OAuth, Outlook OAuth, and Sendmux-managed Amazon SES. Teams can create delivery groups, apply weighted routing, set sender-domain routing, configure per-provider quotas by second, minute, hour, and day, and use automatic failover when a provider becomes unhealthy. This makes Sendmux useful for AI support agents, sales agents, scheduling agents, research agents, monitoring workflows, operations agents, and SaaS platforms that need isolated email identities per customer, workspace, or agent.

Sendmux is built for developers and AI product teams. It provides Management, Sending, and Mailbox APIs, OpenAPI specs, webhooks, Server-Sent Events, SMTP, IMAP, SDKs for TypeScript, Python, Go, PHP, and Ruby, the sendmux CLI, MCP tools, and Sendmux Skills for agent workflows. Teams can use mailbox-scoped API keys, team-level permissions, tenant isolation, delivery logs, metrics, signed webhooks, and encrypted provider credentials.

Pricing is usage-based, with no per-seat fees, no per-mailbox fees, and no minimum commitment. Standard incoming or outgoing email through customer-owned providers is priced at $0.15 / 1,000, Sendmux-managed Amazon SES sending is $0.25 / 1,000, and mailbox storage is $0.02 / GB / month.

Sendmux is a strong fit for teams building AI agents that need durable email identity, inbound email processing, multi-provider email sending, webhook-driven automation, live inbox events, and reliable email infrastructure without maintaining multiple disconnected tools.