Nodemailer

Nodemailer

Node.js email sending library. Works with SMTP, Amazon SES, and other transports. Zero dependencies, full Unicode support.

Quick Start

npm install nodemailer

Basic SMTP Setup

import nodemailer from 'nodemailer';

const transporter = nodemailer.createTransport({
  host: 'smtp.example.com',
  port: 587,
  secure: false,  // true for 465, false for 587
  auth: {
    user: process.env.SMTP_USER,
    pass: process.env.SMTP_PASS,
  },
});

// Send email
await transporter.sendMail({
  from: '"My App" <noreply@example.com>',
  to: 'user@example.com',
  subject: 'Hello',
  text: 'Plain text content',
  html: '<b>HTML content</b>',
});

Transport Configuration

Gmail

// Use App Password (not regular password)
// Enable 2FA, then generate App Password in Google Account settings

const transporter = nodemailer.createTransport({
  service: 'gmail',
  auth: {
    user: 'your-email@gmail.com',
    pass: 'your-app-password',  // 16-character app password
  },
});

Gmail with OAuth2

const transporter = nodemailer.createTransport({
  service: 'gmail',
  auth: {
    type: 'OAuth2',
    user: 'your-email@gmail.com',
    clientId: process.env.GOOGLE_CLIENT_ID,
    clientSecret: process.env.GOOGLE_CLIENT_SECRET,
    refreshToken: process.env.GOOGLE_REFRESH_TOKEN,
  },
});

Outlook/Office365

const transporter = nodemailer.createTransport({
  host: 'smtp.office365.com',
  port: 587,
  secure: false,
  auth: {
    user: 'your-email@outlook.com',
    pass: 'your-password',
  },
});

Amazon SES

import { SES } from '@aws-sdk/client-ses';

const transporter = nodemailer.createTransport({
  SES: {
    ses: new SES({
      region: 'us-east-1',
      credentials: {
        accessKeyId: process.env.AWS_ACCESS_KEY_ID,
        secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY,
      },
    }),
    aws: { SendRawEmailCommand },
  },
});

Resend SMTP

const transporter = nodemailer.createTransport({
  host: 'smtp.resend.com',
  port: 465,
  secure: true,
  auth: {
    user: 'resend',
    pass: process.env.RESEND_API_KEY,
  },
});

SendGrid SMTP

const transporter = nodemailer.createTransport({
  host: 'smtp.sendgrid.net',
  port: 587,
  secure: false,
  auth: {
    user: 'apikey',
    pass: process.env.SENDGRID_API_KEY,
  },
});

Message Options

const message = {
  // Sender
  from: '"Sender Name" <sender@example.com>',

  // Recipients
  to: 'recipient@example.com',
  // Or multiple
  to: 'one@example.com, two@example.com',
  // Or with names
  to: '"User One" <one@example.com>, "User Two" <two@example.com>',

  // CC and BCC
  cc: 'cc@example.com',
  bcc: 'bcc@example.com',

  // Reply-to
  replyTo: 'reply@example.com',

  // Subject
  subject: 'Hello World',

  // Content
  text: 'Plain text body',
  html: '<h1>HTML body</h1>',

  // Priority
  priority: 'high',  // 'high', 'normal', 'low'

  // Custom headers
  headers: {
    'X-Custom-Header': 'value',
  },

  // Message-ID
  messageId: '<unique-id@example.com>',

  // References (for threading)
  references: '<previous-message-id@example.com>',
  inReplyTo: '<previous-message-id@example.com>',
};

await transporter.sendMail(message);

Attachments

const message = {
  from: 'sender@example.com',
  to: 'recipient@example.com',
  subject: 'With attachments',
  text: 'See attachments',
  attachments: [
    // From file
    {
      filename: 'document.pdf',
      path: './files/document.pdf',
    },
    // From buffer
    {
      filename: 'data.json',
      content: Buffer.from(JSON.stringify({ hello: 'world' })),
    },
    // From string
    {
      filename: 'text.txt',
      content: 'Hello World',
    },
    // From URL
    {
      filename: 'image.png',
      path: 'https://example.com/image.png',
    },
    // Embedded image (for HTML)
    {
      filename: 'logo.png',
      path: './logo.png',
      cid: 'logo@myapp',  // Reference in HTML as <img src="cid:logo@myapp">
    },
  ],
};

await transporter.sendMail(message);

Embedded Images

const message = {
  from: 'sender@example.com',
  to: 'recipient@example.com',
  subject: 'With embedded image',
  html: `
    <h1>Hello</h1>
    <img src="cid:logo@myapp" alt="Logo" />
  `,
  attachments: [
    {
      filename: 'logo.png',
      path: './logo.png',
      cid: 'logo@myapp',
    },
  ],
};

Verify Connection

Test configuration before sending.

try {
  await transporter.verify();
  console.log('SMTP connection successful');
} catch (error) {
  console.error('SMTP connection failed:', error);
}

Error Handling

try {
  const info = await transporter.sendMail(message);
  console.log('Message sent:', info.messageId);
} catch (error) {
  if (error.responseCode === 550) {
    console.error('Recipient rejected');
  } else if (error.code === 'ECONNECTION') {
    console.error('Connection failed');
  } else if (error.code === 'EAUTH') {
    console.error('Authentication failed');
  } else {
    console.error('Error:', error.message);
  }
}

Pooled Connections

For high-volume sending, reuse connections.

const transporter = nodemailer.createTransport({
  pool: true,
  host: 'smtp.example.com',
  port: 587,
  secure: false,
  auth: {
    user: process.env.SMTP_USER,
    pass: process.env.SMTP_PASS,
  },
  maxConnections: 5,
  maxMessages: 100,
});

// Close pool when done
transporter.close();

With React Email

import nodemailer from 'nodemailer';
import { render } from '@react-email/components';
import WelcomeEmail from './emails/welcome';

const transporter = nodemailer.createTransport({
  host: 'smtp.example.com',
  port: 587,
  auth: {
    user: process.env.SMTP_USER,
    pass: process.env.SMTP_PASS,
  },
});

async function sendWelcomeEmail(user) {
  const html = await render(WelcomeEmail({
    name: user.name,
    actionUrl: 'https://myapp.com/start',
  }));

  await transporter.sendMail({
    from: '"MyApp" <hello@myapp.com>',
    to: user.email,
    subject: `Welcome, ${user.name}!`,
    html,
  });
}

Next.js API Route

// app/api/contact/route.ts
import { NextResponse } from 'next/server';
import nodemailer from 'nodemailer';

const transporter = nodemailer.createTransport({
  host: process.env.SMTP_HOST,
  port: parseInt(process.env.SMTP_PORT || '587'),
  secure: false,
  auth: {
    user: process.env.SMTP_USER,
    pass: process.env.SMTP_PASS,
  },
});

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

  try {
    await transporter.sendMail({
      from: process.env.SMTP_FROM,
      to: process.env.CONTACT_EMAIL,
      replyTo: email,
      subject: `Contact form: ${name}`,
      text: `From: ${name} <${email}>\n\n${message}`,
      html: `
        <p><strong>From:</strong> ${name} &lt;${email}&gt;</p>
        <p>${message.replace(/\n/g, '<br>')}</p>
      `,
    });

    return NextResponse.json({ success: true });
  } catch (error) {
    console.error('Email error:', error);
    return NextResponse.json(
      { error: 'Failed to send email' },
      { status: 500 }
    );
  }
}

Testing with Ethereal

Free fake SMTP for testing - no emails actually sent.

// Create test account
const testAccount = await nodemailer.createTestAccount();

const transporter = nodemailer.createTransport({
  host: 'smtp.ethereal.email',
  port: 587,
  secure: false,
  auth: {
    user: testAccount.user,
    pass: testAccount.pass,
  },
});

const info = await transporter.sendMail({
  from: 'test@example.com',
  to: 'recipient@example.com',
  subject: 'Test',
  text: 'Test email',
});

// Preview URL
console.log('Preview:', nodemailer.getTestMessageUrl(info));

Environment Variables

# SMTP Configuration
SMTP_HOST=smtp.example.com
SMTP_PORT=587
SMTP_SECURE=false
SMTP_USER=your-username
SMTP_PASS=your-password
SMTP_FROM="My App" <noreply@example.com>

# Or for Gmail
GMAIL_USER=your-email@gmail.com
GMAIL_APP_PASSWORD=your-app-password

Common Transports

Best Practices

1. Use environment variables - Never hardcode credentials
2. Verify connection - Test before sending in production
3. Use pooling - For high-volume sending
4. Handle errors - Implement proper error handling
5. Use OAuth2 - More secure than passwords for Gmail
6. Test with Ethereal - Free testing without sending real emails
7. Set proper From - Use verified sender addresses