Email API for AI Agents: Send, Receive, and Reply in Six Lines

One API key, both directions

Most email APIs stop at sending. Your agent fires a POST, the message goes out, done. The gap appears the moment a customer replies: now you need inbound parsing, threading, and a way to route the reply back to the agent that sent the original. An email API for AI agents wraps both sides into one integration:

import { createClient } from "@mailsai/sdk";
const mails = createClient({ apiKey: process.env.MAILS_API_KEY });

// Send — one call, no SMTP to configure.
await mails.messages.send({
  from: "hello",
  to: "customer@example.com",
  subject: "Your refund #812 is confirmed",
  body_text: "We processed your refund for $49. Reply with any questions.",
});

// Receive — replies arrive as typed, injection-scanned events.
const events = await mails.events.list({
  event_type: "message.received",
  limit: 10,
});
for (const e of events.data) {
  console.log(e.data.extracted_text); // clean reply, quoted history stripped
  console.log(e.injection_score);     // 0.0–1.0; quarantine at 0.5+
  console.log(e.thread_id);           // stable across the conversation
}

The same flow in Python

The Python SDK mirrors the TypeScript one. Install with pip install mailsai and the same six-line pattern works:

from mailsai import MailsClient

mails = MailsClient(api_key=os.environ["MAILS_API_KEY"])

mails.messages.send(
    agent="hello",
    to="customer@example.com",
    subject="Your refund #812 is confirmed",
    body_text="We processed your refund for $49. Reply with any questions.",
)

events = mails.events.list(event_type="message.received", limit=10)
for e in events.data:
    if e.injection_score is not None and e.injection_score >= 0.5:
        flag_for_review(e)  # hold for a person
        continue
    # safe — route to the agent's reply logic
    handle_reply(e)

Per-agent identity and reputation

Each agent you create gets its own email address and its own reputation score. Bounce rate, complaint rate, and engagement metrics are tracked per agent — so one agent that drifts above 0.3 % complaints is suspended automatically before the damage propagates to the rest of your account. For the full identity model, see email for AI agents.

Inbound: events, not mailboxes

The inbound email API turns receiving into an event stream. Each reply to your agent is parsed into structured JSON — sender, subject, clean text body, thread ID — scanned for prompt injection, and delivered to your webhook or polled via the REST API. No IMAP, no MIME, no OAuth refresh tokens.

Transactional sends, agent-shaped

The sends your agents trigger — OTPs, receipts, confirmations, status updates — ride a clean rail because cold outreach is refused at the API. Each send is authenticated end to end (SPF, DKIM, DMARC). For the transactional-specific details, see the transactional email API for AI agents page.

MCP, CLI, and every framework

Beyond the SDKs, the MCP server drops the email API into any MCP-compatible agent: Claude Code, Cursor, Cline, Continue, Windsurf. The CLI sends from a terminal. Framework-specific guides cover the OpenAI Agents SDK, Anthropic SDK, Vercel AI SDK, LangGraph, and Pydantic AI. Read the full email API comparison for 2026 to see how Mails.ai stacks up.

Pricing

The free tier covers 3,000 emails and 3,000 inbound replies a month with one agent — no card required. Pro is $20 a month for 50,000 emails and 50,000 inbound replies across five agents, and Scale is $99 for 250,000 emails and 500,000 inbound replies with unlimited agents. Injection scanning is included on every inbound; intent/entity classification of first-contact mail is available at no extra charge on paid plans. Yearly billing is two months free. See pricing for the full breakdown, or custom domain email for AI agents for branding your agents under your own domain.