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.

1"use server";
2
3import { Reloop } from "reloop-email";
4
5const reloop = new Reloop(process.env.RELOOP_API_KEY!);
6
7export async function sendWelcomeEmail(email: string) {
8  await reloop.emails.send({
9    from: "onboarding@yourdomain.com",
10    to: email,
11    subject: "Welcome",
12    html: "<p>Thanks for signing up.</p>",
13  });
14}

Deploy on Vercel

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