How to Send Emails in Node.js / Next.js – Gmail SMTP & Resend Integration

Sending transactional emails — such as signup confirmation, password reset, or order updates — is a common requirement in web development. In this guide, you'll learn two practical methods to send emails in Node.js / Next.js apps:

• Using Gmail SMTP with Nodemailer
• Using Resend API with a verified domain

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Method 1: Sending Emails Using Gmail SMTP

Step 1: Install Nodemailer

npm install nodemailer
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Step 2: Setup Gmail SMTP Credentials

To use your Gmail account for sending emails:

• Go to your Google Account Settings
• Enable 2-step verification
• Create an App Password
• Use that app password instead of your actual password

In your .env file:

// .env
SMTP_USER=yourgmail@gmail.com
SMTP_PASS=your-app-password
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Step 3: Create Mail Utility

// lib/mailer.ts
import nodemailer from "nodemailer";

if (!process.env.SMTP_USER || !process.env.SMTP_PASS)
  throw new Error("SMTP_USER and SMTP_PASS must be set in .env");


const transporter = nodemailer.createTransport({
  service: "gmail",
  auth: {
    user: process.env.SMTP_USER,
    pass: process.env.SMTP_PASS,
  },
});

export async function sendMail({
  to,
  subject,
  html,
}: {
  to: string;
  subject: string;
  html: string;
}) {
  const mailOptions = {
    from: process.env.SMTP_USER,
    to,
    subject,
    html,
  };

  return await transporter.sendMail(mailOptions);
}
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Step 4: Send Email

// app/api/send-mail/route.ts
import { sendMail } from "@/lib/mailer";

export async function POST(req: Request) {
  const { to, subject, html } = await req.json();

  await sendMail({ to, subject, html });

  return Response.json({ success: true });
}
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Method 2: Sending Emails Using Resend API

Resend is an email API for developers with a clean DX.

Step 1: Install Resend SDK

npm install resend
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Step 2: Get Resend API Key

1. Go to https://resend.com
2. Create a project and verify a domain or email
3. Copy your API key and add it to .env:

// .env
RESEND_API_KEY=your_resend_api_key
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Step 3: Create Resend Utility

// lib/resend.ts
import { Resend } from "resend";

if (!process.env.RESEND_API_KEY)
  throw new Error("RESEND_API_KEY must be set in .env");

export const resend = new Resend(process.env.RESEND_API_KEY);
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Step 4: Send Email Using Resend

// app/api/send-mail/route.ts
import { resend } from "@/lib/resend";

export async function POST(req: Request) {
  const { to, subject, html } = await req.json();

  await resend.emails.send({
    from: "Your Project <noreply@yourdomain.com>",
    to,
    subject,
    html,
  });

  return Response.json({ success: true });
}
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Summary: When to Use What?

| Use Case                       |  Recommended Option             |
|--------------------------------|--------------------------       |
| Quick internal testing         |  Gmail SMTP + Nodemailer        |
| Production with custom domain  |  Resend API (clean + scalable)  |
| No server / client-side send   |  Use EmailJS or Resend + API    |
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Final Thoughts

Both Gmail SMTP and Resend offer great ways to send emails from your app. While Gmail works well for internal or testing use, Resend is ideal for production-grade transactional messaging.

Choose based on scale, branding, and infrastructure flexibility.