Email Integration (Resend + React Email)

You are an expert in sending emails from Vercel-deployed applications — covering Resend (native Vercel Marketplace integration), React Email templates, domain verification, and transactional email patterns.

Vercel Marketplace Setup (Recommended)

Resend is a native Vercel Marketplace integration with auto-provisioned API keys and unified billing.

Install via Marketplace

# Install Resend from Vercel Marketplace (auto-provisions env vars)
vercel integration add resend

Auto-provisioned environment variables:

RESEND_API_KEY — server-side API key for sending emails

SDK Setup

# Install the Resend SDK
npm install resend

# Install React Email for building templates
npm install react-email @react-email/components

Initialize the Client

Current Resend SDK version: 6.9.x (actively maintained, weekly downloads ~1.6M).

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

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

Sending Emails

Basic API Route

// app/api/send/route.ts
import { NextResponse } from "next/server";
import { resend } from "@/lib/resend";

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

  const { data, error } = await resend.emails.send({
    from: "Your App <hello@yourdomain.com>",
    to,
    subject,
    html,
  });

  if (error) {
    return NextResponse.json({ error }, { status: 400 });
  }

  return NextResponse.json({ id: data?.id });
}

Send with React Email Template

// app/api/send/route.ts
import { NextResponse } from "next/server";
import { resend } from "@/lib/resend";
import WelcomeEmail from "@/emails/welcome";

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

  const { data, error } = await resend.emails.send({
    from: "Your App <hello@yourdomain.com>",
    to: email,
    subject: "Welcome!",
    react: WelcomeEmail({ name }),
  });

  if (error) {
    return NextResponse.json({ error }, { status: 400 });
  }

  return NextResponse.json({ id: data?.id });
}

React Email Templates

Template Structure

Organize templates in an emails/ directory at the project root:

emails/
  welcome.tsx
  invoice.tsx
  reset-password.tsx

Example Template

// emails/welcome.tsx
import {
  Body,
  Container,
  Head,
  Heading,
  Html,
  Link,
  Preview,
  Text,
} from "@react-email/components";

interface WelcomeEmailProps {
  name: string;
}

export default function WelcomeEmail({ name }: WelcomeEmailProps) {
  return (
    <Html>
      <Head />
      <Preview>Welcome to our platform</Preview>
      <Body style={{ fontFamily: "sans-serif", backgroundColor: "#f6f9fc" }}>
        <Container style={{ padding: "40px 20px", maxWidth: "560px" }}>
          <Heading>Welcome, {name}!</Heading>
          <Text>
            Thanks for signing up. Get started by visiting your{" "}
            <Link href="https://yourdomain.com/dashboard">dashboard</Link>.
          </Text>
        </Container>
      </Body>
    </Html>
  );
}

Preview Templates Locally

# Start the React Email dev server to preview templates
npx react-email dev

This opens a browser preview at http://localhost:3000 where you can view and iterate on email templates with hot reload.

Upload Templates to Resend (React Email 5.0)

# Upload templates directly from the CLI
npx react-email@latest resend setup

Paste your API key when prompted — templates are uploaded and available in the Resend dashboard.

Dark Mode Support (React Email 5.x)

React Email 5.x (latest 5.2.9, @react-email/components 1.0.8) supports dark mode with a theming system tested across popular email clients. Now also supports React 19.2 and Next.js 16. Use the Tailwind component with Tailwind CSS v4 for email styling:

import { Tailwind } from "@react-email/components";

export default function MyEmail() {
  return (
    <Tailwind>
      <div className="bg-white dark:bg-gray-900 text-black dark:text-white">
        <h1>Hello</h1>
      </div>
    </Tailwind>
  );
}

Upgrade note (v4 → v5): Replace all renderAsync with render. The Tailwind component now only supports Tailwind CSS v4.

Domain Verification

To send from a custom domain (not onboarding@resend.dev), verify your domain in Resend:

Go to Resend Domains
Add your domain
Add the DNS records (MX, SPF, DKIM) to your domain provider
Wait for verification (usually under 5 minutes)

Until your domain is verified, use onboarding@resend.dev as the from address for testing.

Common Patterns

Batch Sending

const { data, error } = await resend.batch.send([
  {
    from: "hello@yourdomain.com",
    to: "user1@example.com",
    subject: "Update",
    html: "<p>Content for user 1</p>",
  },
  {
    from: "hello@yourdomain.com",
    to: "user2@example.com",
    subject: "Update",
    html: "<p>Content for user 2</p>",
  },
]);

Server Action

"use server";
import { resend } from "@/lib/resend";
import WelcomeEmail from "@/emails/welcome";

export async function sendWelcomeEmail(name: string, email: string) {
  const { error } = await resend.emails.send({
    from: "Your App <hello@yourdomain.com>",
    to: email,
    subject: "Welcome!",
    react: WelcomeEmail({ name }),
  });

  if (error) throw new Error("Failed to send email");
}

Broadcast API (February 2026)

Send emails to audiences (mailing lists) managed in Resend:

// Send a broadcast to an audience
const { data, error } = await resend.broadcasts.send({
  audienceId: "aud_1234",
  from: "updates@yourdomain.com",
  subject: "Monthly Newsletter",
  react: NewsletterEmail({ month: "March" }),
});

// Create and manage broadcasts programmatically
const broadcast = await resend.broadcasts.create({
  audienceId: "aud_1234",
  from: "updates@yourdomain.com",
  subject: "Product Update",
  react: ProductUpdateEmail(),
});

// Schedule for later
await resend.broadcasts.send({
  broadcastId: broadcast.data?.id,
  scheduledAt: "2026-03-15T09:00:00Z",
});

Idempotency Keys

Prevent duplicate sends on retries by passing an Idempotency-Key header:

const { data, error } = await resend.emails.send(
  {
    from: "hello@yourdomain.com",
    to: "user@example.com",
    subject: "Order Confirmation",
    react: OrderConfirmation({ orderId: "ord_123" }),
  },
  {
    headers: {
      "Idempotency-Key": `order-confirmation-ord_123`,
    },
  }
);

Resend deduplicates requests with the same idempotency key within a 24-hour window. Use deterministic keys derived from your business logic (e.g., order-confirmation-${orderId}).

Webhook Management API

Create and manage webhooks programmatically instead of through the dashboard:

// Create a webhook endpoint
const { data } = await resend.webhooks.create({
  url: "https://yourdomain.com/api/webhook/resend",
  events: ["email.delivered", "email.bounced", "email.complained", "email.suppressed"],
});

// List all webhooks
const webhooks = await resend.webhooks.list();

// Delete a webhook
await resend.webhooks.remove(webhookId);

Email Status: "suppressed"

Resend now tracks a "suppressed" delivery status for recipients on suppression lists (previous hard bounces or spam complaints). Check for this in webhook events alongside delivered/bounced/complained.

Webhook for Delivery Events

// app/api/webhook/resend/route.ts
import { NextResponse } from "next/server";

export async function POST(req: Request) {
  const event = await req.json();

  switch (event.type) {
    case "email.delivered":
      // Track successful delivery
      break;
    case "email.bounced":
      // Handle bounce — remove from mailing list
      break;
    case "email.complained":
      // Handle spam complaint — unsubscribe user
      break;
  }

  return NextResponse.json({ received: true });
}

Environment Variables

Variable	Scope	Description
`RESEND_API_KEY`	Server	Resend API key (starts with `re_`)

Cross-References

Marketplace install and env var provisioning → ⤳ skill: marketplace
API route patterns → ⤳ skill: routing-middleware
Environment variable management → ⤳ skill: env-vars
Serverless function config → ⤳ skill: vercel-functions

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