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" <noreply@myapp.com>', to: 'user@example.com', 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 <noreply@myapp.com>', to: ['user@example.com'], subject: 'Welcome!', html: '<h1>Welcome</h1>', });

SendGrid

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

await sgMail.send({ to: 'user@example.com', from: 'noreply@myapp.com', 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: 'noreply@myapp.com', Destination: { ToAddresses: ['user@example.com'] }, 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"] = "noreply@myapp.com" msg["To"] = "user@example.com" 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("noreply@myapp.com");
    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

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