How to Send Email in Next.js App Router (2026)

Install the SDK

Run npm install reloop-email and add RELOOP_API_KEY to .env.local. Never expose the key to the client—send only from server components, Server Actions, or Route Handlers.

npm install reloop-email

Server Action example

Create a sendWelcomeEmail action that calls reloop.emails.send after signup. Return success or error to the client without leaking API details.

"use server";

import { Reloop } from "reloop-email";

const reloop = new Reloop(process.env.RELOOP_API_KEY!);

export async function sendWelcomeEmail(email: string) {
  await reloop.emails.send({
    from: "onboarding@yourdomain.com",
    to: email,
    subject: "Welcome",
    html: "<p>Thanks for signing up.</p>",
  });
}

Deploy on Vercel

Add RELOOP_API_KEY to Vercel environment variables. The HTTP API works on Edge Runtime where SMTP does not.