Sendmux

Sendmux is an email inbox API and sending platform for AI agents. It gives each agent a real mailbox to receive email, read threads, process attachments, send replies, and react to new messages through signed webhooks or Server-Sent Events. Sendmux also handles outbound email through Gmail OAuth, Outlook OAuth, SMTP providers, or managed Amazon SES. Teams can route across providers, set quotas from per second to per day, use weighted routing and failover, and connect through MCP, SDKs, CLI, and OpenAPI docs. It is built for agent products, automation teams, support workflows, ops tools, and controlled BYO-provider email setups.