Email for AI Agents: Send, Receive, and Reply Without an SMTP Rabbit Hole

Send and receive under one API key

The minimal email setup for an AI agent is a send API. It works — until the customer replies. At that point you need inbound parsing, threading, and a way to route the reply back to the agent that sent the original message. That is the gap a plain SMTP relay cannot fill:

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

// Sending: one call, no DNS to configure, no domain to verify upfront.
await mails.messages.send({
  agent: "billing",          // creates the agent if it doesn't exist yet
  to: "customer@example.com",
  subject: "Your invoice #441 is ready",
  body_text: "Invoice #441 for August is attached — reply with any questions.",
});
// → billing@yourworkspace.mails.ai, SPF/DKIM/DMARC aligned

// Receiving: replies arrive as typed events, already parsed and injection-scanned.
mails.events.on("message.received", async (event) => {
  // event.body_text  — clean plain-text body, no MIME handling needed
  // event.thread_id  — stable across the whole conversation
  // event.injection_score — 0.0–1.0; quarantine above 0.5
  if ((event.injection_score ?? 0) > 0.5) return;

  // Reply in the same thread — no Message-ID wrangling.
  await mails.messages.reply(event.message_id, {
    body_text: "Got it — I'll process that and follow up by end of day.",
  });
});

Reputation stays per agent, not per account

A shared sending domain fails when one sender misbehaves and the whole domain takes the bounce or complaint hit. Here, each AI email agent has its own reputation score. An agent whose complaint rate drifts above 0.3 % — below the upstream threshold of 0.5 % — is suspended automatically before the damage propagates. Your other agents keep sending.

For higher-volume workloads or when a single agent’s reputation needs to be fully isolated from the shared pool, automated dedicated IP warm-up moves that agent onto its own IP without a manual warmup schedule.

Custom domain, same model

By default agents send from their built-in address on the workspace subdomain — working email in one API call, no DNS required. When your agents need to carry your brand, connect a custom domain and every agent on it sends as agent@yourcompany.com, authenticated end to end. Custom domain email for AI agents covers the DNS steps — they’re generated for you and verified automatically.

What it costs

The free tier covers 3,000 sends and 3,000 inbound messages a month with one agent — no card required. Beyond that: $0.001 per outbound message, $0.002 per inbound including parsing and the injection scan, and $0.003 more for intent/entity classification if you want routing decided before your model runs. No monthly minimum, no per-seat fee.