Migrate from Resend

Install the SDK

npm i retransmit.dev

Create an API key on the dashboard  and put it in RETRANSMIT_API_KEY. Your Resend key keeps working until you remove it, so you can run both side by side while you switch traffic.

Verify your domain

Domain verification does not carry over. Add your sending domain in the dashboard and publish the SPF and DKIM records it gives you. Sends from an unverified domain are rejected with domain_not_verified. See Domains.

Swap the client

The constructor and the send call have the same shape.

import { Resend } from "resend";
 
const resend = new Resend(process.env.RESEND_API_KEY);
 
const { data, error } = await resend.emails.send({
  from: "Acme <hello@yourdomain.com>",
  to: "user@example.com",
  replyTo: "support@yourdomain.com",
  subject: "Your receipt",
  html: "<p>Thanks for your order!</p>",
  text: "Thanks for your order!",
  tags: [{ name: "category", value: "receipt" }],
});

import { Retransmit } from "retransmit.dev";
 
const retransmit = new Retransmit(process.env.RETRANSMIT_API_KEY);
 
const { data, error } = await retransmit.emails.send({
  from: "Acme <hello@yourdomain.com>",
  to: "user@example.com",
  replyTo: "support@yourdomain.com",
  subject: "Your receipt",
  html: "<p>Thanks for your order!</p>",
  text: "Thanks for your order!",
  tags: [{ name: "category", value: "receipt" }],
});

data.id identifies the email in Get Email and in webhook events. The response also carries status (queued) and created_at. Errors have a code and a message. The codes are listed under Errors.

Batch sends move the same way: resend.batch.send([...]) becomes retransmit.batch.send([...]). See Send Batch.

Render React Email to HTML

Resend accepts a react prop and renders it for you. Retransmit does not render templates, so call React Email’s render yourself and pass the result as html. Your templates do not change.

import { Resend } from "resend";
import { WelcomeEmail } from "./emails/welcome";
 
const resend = new Resend(process.env.RESEND_API_KEY);
 
await resend.emails.send({
  from: "Acme <hello@yourdomain.com>",
  to: "user@example.com",
  subject: "Welcome to Acme",
  react: <WelcomeEmail name="Jane" />,
});

import { Retransmit } from "retransmit.dev";
import { render } from "@react-email/components";
import { WelcomeEmail } from "./emails/welcome";
 
const retransmit = new Retransmit(process.env.RETRANSMIT_API_KEY);
 
const email = <WelcomeEmail name="Jane" />;
 
await retransmit.emails.send({
  from: "Acme <hello@yourdomain.com>",
  to: "user@example.com",
  subject: "Welcome to Acme",
  html: await render(email),
  text: await render(email, { plainText: true }),
});

A few notes on render:

• render is exported by @react-email/components, which you already have if you use React Email. If you want a smaller dependency, install @react-email/render and import it from there.
• Since React Email 1.0, render returns a promise. On older versions it returns the string directly, so drop the await.
• { plainText: true } produces the text body from the same component. It is optional, but sending both html and text helps deliverability.
• Rendering happens in your process, so a template error surfaces before the request goes out. Nothing is queued.

For a batch, render each email before building the array.

Move your webhooks

Create an endpoint on the dashboard’s Webhooks page and point it at your handler. Retransmit uses the same event names as Resend for email (email.sent, email.delivered, email.bounced, email.opened, and so on), but the payload and the signature differ:

• Deliveries are signed with retransmit-timestamp and retransmit-signature headers, not Svix headers. Replace the Svix verification with the check in Verifying signatures.
• The payload shape is described under Webhooks. Update your handler to read data.emailId and the event fields from there.