Send with Vercel Functions

You need a verified domain and an API key.

#1. Install

npm install @usend/node

#2. Add the key as an environment variable

vercel env add USEND_API_KEY

Or add it in the project's Settings → Environment Variables. Use a sending_access key, and a separate key for Preview and Production.

#3. The function

import { Usend } from '@usend/node';

const usend = new Usend(process.env.USEND_API_KEY);

export async function POST(request: Request) {
  const { email } = await request.json();

  const { data, error } = await usend.emails.send({
    from: 'Acme <[email protected]>',
    to: [email],
    subject: 'Welcome to Acme',
    html: '<p>Thanks for signing up.</p>',
  });

  if (error) return Response.json({ error }, { status: 502 });
  return Response.json({ id: data.id });
}

This is a Web-standard handler: it works in a plain Vercel project (api/ folder) and in a Next.js route handler. For a Next.js app see Send with Next.js.

#4. Deploy and test

vercel deploy
curl -X POST https://your-project.vercel.app/api/send \
  -H 'Content-Type: application/json' -d '{"email":"[email protected]"}'

#Tips

• Await the send inside the function. Serverless functions can be frozen as soon as they respond, so a fire-and-forget request may never leave.
• Use an idempotency key if your function can be retried, so a retry does not send twice.
• Receive delivery events with a webhook pointing at another function.