AI Email Platform for Developers: Send, Receive, and Contain Agent Mail

Built for a sender that is a program

Most email platforms assume a human decided to press send. When the sender is an agent, two assumptions break: it has to read what comes back, and it cannot be trusted with unlimited discretion about what goes out. Everything here follows from those two.

Inbound arrives as data. Not a MIME blob and not an IMAP loop — a typed event with the parsed text, the thread, the sender’s reputation, and a prompt-injection score your code can branch on:

{
  "type": "message.received",
  "injection_score": 0.99,           // always present
  "sender_reputation": 0.30,         // always present
  "intent": "ask_question",          // when classification is enabled
  "entities": { "invoice": "221" },
  "data": {
    "from": { "address": "attacker@example.net" },
    "injection_categories": ["instruction_override", "data_exfil"],
    "quarantined": true
  }
}

The limits are in the API, not in your prompt

An agent that was argued into sending outreach still cannot send it: cold and bulk mail come back 422 cold_email_prohibited with a machine-readable reason, a sandbox to test against, and a second independent review if the verdict looks wrong. Reputation is scored per agent and auto-suspends at a 0.3% complaint rate, so one agent’s bad week is contained rather than shared.

That refusal is the platform, not a limitation of it. It is the reason a shared sending estate is worth being on at all.

Surfaces

A REST API, TypeScript and Python SDKs, and a 20-tool MCP server for Claude Desktop, Claude Code, Cursor, Cline, Continue and Windsurf. Source and runnable examples are on GitHub. Free covers 3,000 emails and 3,000 inbound replies a month with no card.

For a deeper look at the concepts behind the platform — DefinedTerm schema, inbound event structure, and security model — see the AI email platform glossary entry. For the operational playbook — routing inbound by classified intent, monitoring per-agent reputation, and managing sending policy — see AI email management. For the underlying infrastructure — DNS authentication, deliverability, IP warm-up, and reputation isolation — see email infrastructure for AI agents.