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AI Email Platform for Developers: Send, Receive, and Contain Agent Mail
An AI email platform in this sense is infrastructure your software builds on, not an assistant that drafts your replies. Mails.ai gives every AI agent its own sending and receiving address, delivers inbound mail as structured JSON events with a prompt-injection score attached, and refuses cold or bulk mail inside the send call — so an autonomous agent can operate email without being able to spend a sending reputation it didn't build.
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": "reply.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_prohibitedwith 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 sends and 3,000 inbound a month with no card.
Frequently asked questions
Is this an AI writing assistant for my inbox?
No. If you want AI to help you write your own email, this is the wrong tool — use an inbox assistant. This is an API your code calls: your agent gets its own address, and you get structured inbound and enforced sending limits.
How is it different from Resend, Postmark, SendGrid or SES?
Those are excellent send APIs. Two things they don't do for an autonomous agent: give it an inbox that arrives as parsed, injection-scanned events rather than raw MIME, and constrain what it may send. Both matter specifically because the sender is a program acting on text it was handed.
How is it different from AgentMail?
The closest comparison in the category. The main differences are a real inbound prompt-injection firewall with auto-quarantine, per-agent reputation scoring with auto-suspension, and an outbound classifier that refuses cold mail. AgentMail's inbound safety is allow and block lists, so an agent still reads untrusted bodies unscanned.
Can I run it on my own domain?
Yes. Verify a custom domain and agents send from it with per-domain DKIM. Paid tiers can also be pinned to an isolated sending subdomain or a dedicated IP for reputation isolation.
What can I evaluate before committing anything?
All of it. A test key runs the complete request path — validation, firewall, threading, events, webhooks — and transmits nothing, and it unlocks an inbound simulator so the receive half can be built and verified before any mail moves. No card, no domain, no DNS.
Explore the product
Built for agents.
Self-serve in minutes.
The API is live and self-serve. Drop ~6 lines into your agent and ship.
$ npm install @mailsai/sdk