Sendmux

Sendmux is an email inbox API and sending platform for AI agents. It gives every agent a real email identity: a dedicated mailbox that can receive inbound email, read threads, process attachments, use cleaned message content, send replies, and react to new messages through signed webhooks or Server-Sent Events.

For outbound email, Sendmux lets teams send through Gmail OAuth, Outlook OAuth, SMTP providers, or managed Amazon SES. Delivery groups support weighted routing, sender-domain routing, provider health checks, automatic failover, and per-provider quotas from per second to per day. That makes it useful for agent products, automation teams, support workflows, ops agents, platform builders, and BYO-provider cold email setups that need controlled sending from AI tools.

For inbound email, Sendmux mailboxes support custom domains with SPF, DKIM, and DMARC, mailbox-scoped API keys, sender filters, folders, labels, attachments, raw .eml downloads, IMAP retrieval, and SMTP.

Key Features:

• Email inbox API for AI agents
• Dedicated agent mailboxes
• Multi-provider email sending
• Managed Amazon SES sending
• Per-provider quotas and throttling
• Weighted routing and failover
• Signed webhooks and SSE events
• Mailbox API for threads and attachments
• MCP, SDKs, CLI, and Sendmux Skills
• Usage-based pricing with no mailbox fees

Main Use Cases:

• AI customer support agents with real inboxes
• Sales and outreach agents using customer-owned providers
• Scheduling and executive-assistant agents
• Research and monitoring agents that process email updates
• Ops, finance, and vendor workflow agents
• Multi-tenant SaaS platforms needing isolated mailboxes
• Automation agencies managing client email workflows
• Internal tools that need webhook-driven email automation