Resend: your agent's email backbone. — DeltaForceOS

◢ The stack

Resend

Transactional + outbound email API designed for agents

Free 3k/mo · $20/mo

◢ The build · 4 steps · 10 min

Follow these in order. Don't skip.

Step 01 / 04

Sign up + add a domain

Resend dashboard — resend.com → Sign up → Domains → Add Domain.

▸Use a domain you own (sending from gmail.com is blocked — it's not yours)
▸Resend gives you 3 DNS records: SPF, DKIM, MX (return-path). Add all three at your registrar.
▸Click Verify. Usually green within 5 minutes; sometimes 1 hour.

◆ Watch out

Don't skip DKIM. Without it, Gmail and Outlook send you to spam by default. The whole reason to use Resend over a random SMTP is deliverability.

Step 02 / 04

Get the API key

▸Dashboard → API Keys → Create API Key
▸Permissions: Sending access (read-only on everything else for safety)
▸Copy the key — only shown once

.env.local

1RESEND_API_KEY=re_...

Step 03 / 04

Send your first email

Terminal

1npm install resend

src/lib/email.ts

1import { Resend } from "resend";
2 
3const resend = new Resend(process.env.RESEND_API_KEY);
4 
5export async function sendEmail(args: {
6  to: string;
7  subject: string;
8  html: string;
9}) {
10  const { data, error } = await resend.emails.send({
11    from: "Your Name <noreply@yourdomain.com>",
12    to: args.to,
13    subject: args.subject,
14    html: args.html,
15  });
16  if (error) throw new Error(error.message);
17  return data;
18}

src/app/api/test-email/route.ts

1import { sendEmail } from "@/lib/email";
2 
3export async function POST() {
4  const result = await sendEmail({
5    to: "you@example.com",
6    subject: "Hello from my agent",
7    html: "<h1>It works.</h1><p>Your agent just emailed you.</p>",
8  });
9  return Response.json(result);
10}

Step 04 / 04

Use React Email for real templates

Hard-coded HTML strings are a maintenance nightmare. React Email lets you compose emails like normal components.

Terminal

1npm install @react-email/components react-email

src/emails/welcome.tsx

1import {
2  Html, Head, Body, Container, Heading, Text, Button, Hr,
3} from "@react-email/components";
4 
5export default function Welcome({ name }: { name: string }) {
6  return (
7    <Html>
8      <Head />
9      <Body style={{ backgroundColor: "#0a0a0a", color: "#fafafa", fontFamily: "Geist, sans-serif" }}>
10        <Container style={{ maxWidth: 560, padding: "32px 24px" }}>
11          <Heading style={{ fontSize: 28, marginBottom: 16 }}>
12            Welcome, {name}.
13          </Heading>
14          <Text style={{ fontSize: 15, lineHeight: 1.6, color: "#b4b4b8" }}>
15            Your agent is live. Below is your first task — reply to this email
16            with anything and the agent will respond.
17          </Text>
18          <Button
19            href="https://yourdomain.com/dashboard"
20            style={{
21              background: "#34d399", color: "#000", padding: "12px 20px",
22              borderRadius: 4, fontWeight: 600, textDecoration: "none",
23            }}
24          >
25            Open dashboard →
26          </Button>
27          <Hr style={{ borderColor: "#222", margin: "32px 0" }} />
28          <Text style={{ fontSize: 12, color: "#666" }}>
29            Sent by your agent · reply STOP to unsubscribe.
30          </Text>
31        </Container>
32      </Body>
33    </Html>
34  );
35}

src/lib/email.ts (updated)

1import { Resend } from "resend";
2import Welcome from "@/emails/welcome";
3 
4const resend = new Resend(process.env.RESEND_API_KEY);
5 
6export async function sendWelcome(to: string, name: string) {
7  return resend.emails.send({
8    from: "You <noreply@yourdomain.com>",
9    to,
10    subject: `Welcome, ${name}`,
11    react: Welcome({ name }),
12  });
13}

◆ Ship-it checklist

5 CHECKS

Domain verified (SPF + DKIM + MX all green)
API key in .env.local + Vercel
src/lib/email.ts wraps Resend calls
At least one React Email template in src/emails/
You sent a test email and it landed in your inbox (not spam)

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