Resend with Express: the guide's string-literal key is a placeholder, read it from the environment

TL;DR

ts import express, { Request, Response } from 'express'; import { Resend } from 'resend'; const app = express(); const resend = new Resend(process.env.RESEND\_API\_KEY); app.post('/send', async (req: Request, res: Response) => { try { const { data, error } = await resend.emails.send({ from: '[SENDER]', to: ['[RECIPIENT]'], subject: 'Hello World', html: '<strong>It works!</strong>', }); if (error) { return res.status(400).json({ error: error.message }); } return res.json({ id: data.id }); } catch (err) { return res.status(502).json({ error: 'email provider unreachable' }); } });

import express, { Request, Response } from 'express';
import { Resend } from 'resend';

const app = express();
const resend = new Resend(process.env.RESEND_API_KEY);

app.post('/send', async (req: Request, res: Response) => {
  try {
    const { data, error } = await resend.emails.send({
      from: '[SENDER]',
      to: ['[RECIPIENT]'],
      subject: 'Hello World',
      html: '<strong>It works!</strong>',
    });
    if (error) {
      return res.status(400).json({ error: error.message });
    }
    return res.json({ id: data.id });
  } catch (err) {
    return res.status(502).json({ error: 'email provider unreachable' });
  }
});

Steps

1. ```ts

import express, { Request, Response } from 'express'; import { Resend } from 'resend';

const app = express(); const resend = new Resend(process.env.RESENDAPIKEY);

app.post('/send', async (req: Request, res: Response) => { try { const { data, error } = await resend.emails.send({ from: '[SENDER]', to: ['[RECIPIENT]'], subject: 'Hello World', html: '<strong>It works!</strong>', }); if (error) { return res.status(400).json({ error: error.message }); } return res.json({ id: data.id }); } catch (err) { return res.status(502).json({ error: 'email provider unreachable' }); } });

2. - The guide writes `new Resend("re_xxxxxxxxx")`. That literal is a placeholder.
 In real code it must be `process.env.RESEND_API_KEY`, loaded from the
 environment, never committed.
- Two failure channels: `error` for API rejections, thrown exceptions for
 transport problems. Handle both or one of them becomes an unhandled rejection
 that crashes the process.
- Do not echo the raw provider error object to the HTTP client. Map it to a
 status and a short message.

## When to use

You are seeing this: That literal is a placeholder. Use this skill when you run into "Resend with Express: the guide's string-literal key is a placeholder, read it from the environment".

## When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

## Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

## Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Resend's Express guide constructs the client inline and sends inside a route handler. Verified live at https://resend.com/docs/send-with-express. The key-as-literal in the guide is a placeholder; production code must read it from the environment.