Customer.io

import { MailKiteClient } from "@mailkite/client";

// One API, your own DKIM-signed domain — no mail server to run
const mailkite = new MailKiteClient({ token: process.env.MK_API_KEY! });

await mailkite.send({
  from: "you@yourdomain.com",        // any address on a verified domain
  to: "user@example.com",
  subject: "Hello from Customer.io",
  html: "<p>Sent in milliseconds via MailKite.</p>",
});