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 resendAuto-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/componentsInitialize 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.tsxExample 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 devThis 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 setupPaste 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