SMTP

Runs through the exact same validation, quota, domain-verification, and suppression handling as POST /emails — nothing sent over SMTP bypasses those guardrails. One email per DATA transaction; every RCPT TO address not already in the message's To/Cc headers is delivered as bcc — except when the message has no To header at all (regardless of Cc), in which case those addresses become to instead, since to is required. Any X-* message header is passed through unchanged, and a plain Idempotency-Key message header works the same way as the REST API's header of the same name.

• Host: smtp.irisend.com
• Ports: 587 (STARTTLS, required before authenticating) or 465 (implicit TLS). 2587/2465 are the same two listeners, for networks that block the standard mail ports.
• AUTH: PLAIN or LOGIN only — no plaintext AUTH without TLS first.
• Username: irisend (resend also works, for a drop-in migration)
• Password: any API key — full_access and sending_access both work
• Max message size: 40MB, including attachments.

import nodemailer from "nodemailer";

const transport = nodemailer.createTransport({
  host: "smtp.irisend.com",
  port: 587, // or 465 for implicit TLS — both work the same way
  secure: false, // true only for port 465
  auth: {
    user: "irisend", // or "resend", for a drop-in migration
    pass: "ir_8fK3mQ1z_9pR2vT6yB4wL0nC7xE1sH5dJ", // your Irisend API key
  },
});

await transport.sendMail({
  from: "[email protected]",
  to: "[email protected]",
  subject: "Your receipt",
  html: "<p>Thanks for your order.</p>",
  text: "Thanks for your order.",
  headers: { "X-Entity-Ref-ID": "order_8841", "Idempotency-Key": "order-8841-receipt" },
});