email-sending

Email Sending

Node.js (Nodemailer)

import nodemailer from 'nodemailer';

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

await transporter.sendMail({
  from: '"My App" <[email protected]>',
  to: '[email protected]',
  subject: 'Welcome!',
  html: '<h1>Welcome</h1><p>Thanks for signing up.</p>',
});

Transactional Email Services

Resend (recommended for simplicity)

import { Resend } from 'resend';

const resend = new Resend(process.env.RESEND_API_KEY);

await resend.emails.send({
  from: 'My App <[email protected]>',
  to: ['[email protected]'],
  subject: 'Welcome!',
  html: '<h1>Welcome</h1>',
});

SendGrid

import sgMail from '@sendgrid/mail';
sgMail.setApiKey(process.env.SENDGRID_API_KEY!);

await sgMail.send({
  to: '[email protected]',
  from: '[email protected]',
  templateId: 'd-abc123',        // Dynamic template
  dynamicTemplateData: { name: 'John', link: resetUrl },
});

Amazon SES (via AWS SDK v3)

import { SESv2Client, SendEmailCommand } from '@aws-sdk/client-sesv2';

const ses = new SESv2Client({ region: 'us-east-1' });
await ses.send(new SendEmailCommand({
  FromEmailAddress: '[email protected]',
  Destination: { ToAddresses: ['[email protected]'] },
  Content: {
    Simple: {
      Subject: { Data: 'Welcome!' },
      Body: { Html: { Data: htmlContent } },
    },
  },
}));

Email Templates

React Email (recommended for React projects)

// emails/welcome.tsx
import { Html, Head, Body, Container, Text, Button } from '@react-email/components';

export function WelcomeEmail({ name, url }: { name: string; url: string }) {
  return (
    <Html>
      <Head />
      <Body style={{ fontFamily: 'sans-serif' }}>
        <Container>
          <Text>Welcome, {name}!</Text>
          <Button href={url} style={{ background: '#000', color: '#fff', padding: '12px 20px' }}>
            Get Started
          </Button>
        </Container>
      </Body>
    </Html>
  );
}

// Render to HTML string
import { render } from '@react-email/render';
const html = await render(<WelcomeEmail name="John" url="https://app.com" />);

MJML (framework-agnostic)

import mjml2html from 'mjml';

const { html } = mjml2html(`
  <mjml>
    <mj-body>
      <mj-section>
        <mj-column>
          <mj-text>Welcome, {{name}}!</mj-text>
          <mj-button href="{{url}}">Get Started</mj-button>
        </mj-column>
      </mj-section>
    </mj-body>
  </mjml>
`);

Python

from email.message import EmailMessage
import aiosmtplib

msg = EmailMessage()
msg["From"] = "[email protected]"
msg["To"] = "[email protected]"
msg["Subject"] = "Welcome!"
msg.set_content("Welcome!", subtype="html")

await aiosmtplib.send(msg, hostname=SMTP_HOST, port=587,
    username=SMTP_USER, password=SMTP_PASS, start_tls=True)

Java (Spring Mail)

@Service
public class EmailService {
    @Autowired private JavaMailSender mailSender;
    @Autowired private TemplateEngine templateEngine; // Thymeleaf

    public void sendWelcome(String to, String name) {
        var ctx = new Context();
        ctx.setVariable("name", name);
        String html = templateEngine.process("welcome", ctx);

        var message = mailSender.createMimeMessage();
        var helper = new MimeMessageHelper(message, true);
        helper.setTo(to);
        helper.setFrom("[email protected]");
        helper.setSubject("Welcome!");
        helper.setText(html, true);
        mailSender.send(message);
    }
}

Anti-Patterns

Anti-Pattern	Fix
Sending email in request handler	Use background job queue (BullMQ, Celery)
No retry on transient failure	Retry with exponential backoff (3 attempts)
Hardcoded from address	Use env var, match verified domain
HTML without plain text fallback	Always include both HTML and text versions
No unsubscribe header	Add List-Unsubscribe header (required by Gmail/Yahoo)
Sending from unverified domain	Set up SPF, DKIM, DMARC records

Production Checklist

• SPF, DKIM, DMARC DNS records configured
• Domain verified with email provider
• List-Unsubscribe header on marketing emails
• Bounce and complaint handling (webhook)
• Email sending via background queue (not in request)
• Rate limiting to stay within provider limits
• Plain text fallback for all HTML emails
• Template preview/testing before deploy