Integrating Resend for Transactional Email Sending

Integrating Resend for Transactional Email Sending

We have encountered projects where transactional emails never reached users: SMTP servers blocked them, DKIM was not configured, and templates had to be coded in raw HTML. As a result, lead forms, confirmations, and password resets were lost — the business took a hit. Losses from undelivered emails reached 15% conversion, and customers switched to competitors. Resend solves these problems out of the box: a modern email API with native React Email support, a free tier of 3000 emails per month, and automated deliverability setup. In this article we'll show how we connect Resend in real projects and what results it yields.

Why Resend instead of SMTP or legacy services?

Manual SMTP configuration means N+1 attempts, low deliverability, spam filters. Resend offers a ready API that guarantees delivery. Unlike SendGrid and Amazon SES, Resend is simpler: no need to manually set up DKIM/SPF — everything is automatic. Plus, React Email works out of the box, speeding up template development by orders of magnitude. Our experience shows: integration time is cut in half compared to classic solutions, and revenue from restored notifications pays for itself in 1-2 months.

Resend is 2x faster to set up than classic SMTP.

How we integrate Resend into your application

We connect Resend, configure your domain, develop React Email templates, set up batch sending and logging. We use TypeScript and Next.js 14 with Server Actions for sending from server components.

Installation and first send

npm install resend 

import { Resend } from 'resend'; const resend = new Resend(process.env.RESEND_API_KEY); // Simple send const { data, error } = await resend.emails.send({ from: 'Acme <[email protected]>', to: ['[email protected]'], subject: 'Welcome to Acme!', html: '<h1>Hello!</h1><p>Thanks for registering.</p>', }); if (error) { console.error('Email error:', error); } 

With React Email templates

import { Resend } from 'resend'; import { render } from '@react-email/render'; import WelcomeEmail from './emails/WelcomeEmail'; const resend = new Resend(process.env.RESEND_API_KEY); export async function sendWelcomeEmail(user: { email: string; name: string }) { const html = render( <WelcomeEmail name={user.name} loginUrl="https://app.acme.com/login" /> ); await resend.emails.send({ from: 'Acme Team <[email protected]>', to: user.email, subject: 'Welcome to Acme!', html, }); } 

How does batch sending work?

Batch sending allows you to send up to 100 emails in a single HTTP request. This is critical for invoice mailings, notifications, or confirmations during peak load. Resend processes them in parallel, saving time and resources.

await resend.batch.send([ { from: '[email protected]', to: '[email protected]', subject: 'Your invoice is ready', html: invoiceHtml1, }, { from: '[email protected]', to: '[email protected]', subject: 'Your invoice is ready', html: invoiceHtml2, }, ]); 

How to configure a domain for Resend (step by step)

1. Add your domain in the Resend Dashboard → Domains.
2. Add DNS records: SPF (TXT), DKIM (TXT × 3), Return-Path (MX).
3. Wait for verification (usually under 5 minutes).

After verification, you can use from: '[email protected]' instead of @resend.dev. Resend documentation states: "With proper DKIM and SPF setup, deliverability exceeds 99%."

How to avoid landing in spam?

Use a dedicated sending domain, set up a DMARC record, and monitor IP reputation through webhooks. Regularly clean inactive users. Resend automatically manages reputation, but basic list hygiene matters.

Webhooks for status tracking

Resend sends webhooks when email status changes. Below is a full Node.js handler example with Express:

app.post('/api/webhooks/resend', express.raw({ type: 'application/json' }), async (req, res) => { const signature = req.headers['resend-signature']; const event = JSON.parse(req.body); switch (event.type) { case 'email.sent': await db.emailLogs.update({ emailId: event.data.email_id, status: 'sent' }); break; case 'email.delivered': await db.emailLogs.update({ emailId: event.data.email_id, status: 'delivered' }); break; case 'email.bounced': await db.users.markEmailBounced(event.data.to[0]); break; case 'email.complained': await db.users.unsubscribe(event.data.to[0]); break; } res.status(200).end(); }); 

Common issues and solutions

• Authorization error: wrong API key. Check the RESEND_API_KEY environment variable.
• Emails not delivered: incorrect domain setup or landing in spam. Use webhooks for tracking and configure SPF/DKIM strictly per instructions.
• Rate limit exceeded: the free tier is capped at 3000 emails per month. If needed, upgrade to a paid plan or use batch sending to optimize.

What the Resend integration includes

Timeline and pricing

Basic Resend integration with 2-3 React Email templates takes 1-2 days. Extended version with domain, webhooks, and logging takes 3-4 days. Pricing is calculated individually based on project complexity. Leave a request — we will find the optimal solution. Get a consultation on Resend integration: our engineers with over 5 years of experience will help you set up reliable email sending. We guarantee high deliverability and post-launch support.