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.