Send a welcome email from Node.js

In this tutorial you add a welcome email to a Node.js sign-up flow. By the end, every new account gets one welcome email, even if the sign-up request is retried.

You’ll need: a verified sending domain, an API key with the sending scope, Node.js 18+, and an Express app. See the Quickstart if you haven’t set these up.

Install the SDK

npm install @sendflit/sdk express

pnpm add @sendflit/sdk express

The SDK has no dependencies of its own. Install it once your package is published; until then, see the SDK status table.

Create the client

Store the key in an environment variable. Never hard-code it.

// lib/sendflit.js
import SendFlit from "@sendflit/sdk";

export const sendflit = new SendFlit({ apiKey: process.env.SENDFLIT_API_KEY });

Send on sign-up, with an idempotency key

The key identifies the business event, not the request. Using the user’s ID means a retried request sends the same email once.

// routes/signup.js
import express from "express";
import { sendflit } from "../lib/sendflit.js";

const app = express();
app.use(express.json());

app.post("/signup", async (req, res) => {
  const { email, name } = req.body;
  const user = await createUser({ email, name }); // your code

  await sendflit.send({
    from: "hello@yourdomain.com",
    to: user.email,
    subject: `Welcome, ${name}`,
    html: `<p>Thanks for signing up, ${name}.</p><p><a href="https://app.yourdomain.com/start">Get started</a></p>`,
  }, `welcome-${user.id}`);

  res.status(201).json({ id: user.id });
});

app.listen(3000);

Send the welcome email after the user is saved, not before. If the save fails, nothing is sent.

Handle failures

Retryable failures (429 and 5xx) are retried by the SDK. A permanent failure, such as an unverified domain (403), is thrown, so log it and alert:

import { SendFlitError } from "@sendflit/sdk";

try {
  await sendflit.send(email, `welcome-${user.id}`);
} catch (err) {
  if (err instanceof SendFlitError && err.status === 403) {
    console.error("Domain not verified or recipient suppressed", err.body);
  }
  throw err;
}

See Errors, retries and limits for every status code.

Test it

curl https://api.sendflit.com/v1/emails/<id> \
  -H "Authorization: Bearer $SENDFLIT_KEY"

Retry the same sign-up request with the same user.id to confirm the second send doesn’t deliver a duplicate.

Handle bounces with webhooks to keep bad addresses out of future sends.
Idempotency for a deeper look at safe retries.

Get started

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Send a welcome email from Node.js

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