Moving your app's email to Resend

1. Sign up for Resend.
2. Go to Domains in the sidebar and click Add domain.
3. Type your domain: yourdomain.com.
4. Pick a region. If most of your users are in Europe or Turkey, the EU region (eu-west-1) makes sense.

The region is chosen when you add the domain. Changing it later may mean deleting and re-adding the domain, so pick the right one up front.

Once the domain is added, Resend shows a few DNS records (MX, a TXT for SPF, a TXT for DKIM). They're how you say "Resend may send email on behalf of this domain."

If you use Cloudflare: the dashboard offers an automatic setup for Cloudflare. You sign in to your Cloudflare account, approve, and the records are added in one click.

If you use another DNS provider: enter the records the dashboard shows into your DNS panel one by one. Watch out for two things:

• Don't repeat your domain in the Name field. Type just send, not send.yourdomain.com. Most panels append the domain for you.
• If you're entering them manually in Cloudflare, the records must not be proxied (DNS only, grey cloud).

Don't copy record values from this guide. Enter exactly what you see in your Resend dashboard. The values differ per account and domain.

After adding the records, click Verify in Resend. Verification can take anywhere from a few minutes to a few hours. Mine took about 20 minutes.

Extra tip: a DMARC record. DMARC tells receiving servers what to do when SPF or DKIM fails. If you don't have one, add it:

Type:  TXT
Name:  _dmarc
Value: v=DMARC1; p=none;

If your domain already has a _dmarc record, don't add a second one. A domain has only one DMARC record.

1. Go to API Keys in the sidebar and click Create API key.
2. Give it a name (e.g. app-prod).
3. Permission: choose Sending access, not Full access. Your app only needs to send email; if the key leaks, nobody should be able to manage your account with it.
4. Domain: restrict it to this domain only.

The domain may not show up in the list until it's verified. In that case, create the key for now, then once verification is done, create a new key restricted to the domain and delete the old one.

The key starts with re_ and is shown only once. Save it in your password manager right away. Don't put it in code, in your repo or in a screenshot. On the server, keep it in an environment variable:

RESEND_API_KEY=re_xxxxxxxx

Two ways. Use SMTP if you barely want to touch your code, the API if you're on Node.js / Next.js.

Over SMTP (almost no code changes)

Change your app's SMTP settings to:

Host:     smtp.resend.com
Username: resend
Password: your API key (re_...)
Port:     465 (SSL) or 587 (STARTTLS)

The sender address must be on your verified domain, e.g. notifications@yourdomain.com. You can't send from another domain.

WordPress example. First, read the key from an environment variable in wp-config.php:

define( 'RESEND_API_KEY', getenv( 'RESEND_API_KEY' ) );

Then add this to your theme's functions.php or a small plugin:

add_action( 'phpmailer_init', function ( $phpmailer ) {
    $phpmailer->isSMTP();
    $phpmailer->Host       = 'smtp.resend.com';
    $phpmailer->SMTPAuth   = true;
    $phpmailer->Username   = 'resend';
    $phpmailer->Password   = RESEND_API_KEY;
    $phpmailer->Port       = 465;
    $phpmailer->SMTPSecure = 'ssl';
    $phpmailer->From       = 'notifications@yourdomain.com';
    $phpmailer->FromName   = 'Your App';
} );

Every email WordPress sends now goes out through Resend.

Over the API (Node.js / Next.js)

Install the package:

npm install resend

Send an email:

import { Resend } from 'resend';

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

const { data, error } = await resend.emails.send({
  from: 'Your App <notifications@yourdomain.com>',
  to: ['user@example.com'],
  subject: 'Reset your password',
  html: '<p>Click the link to reset your password.</p>',
});

if (error) console.error(error);

You can also have Claude Code do this for you:

I'm moving all the email this project sends to Resend.

1. Find every place in the project that sends email (SMTP settings, mail library, wp_mail, nodemailer, etc.) and list them for me.
2. If it uses SMTP, change the settings to smtp.resend.com, username "resend", port 465. Read the password from the RESEND_API_KEY environment variable.
3. Set the sender address to notifications@<MY DOMAIN>.
4. Never write the API key to any file or commit it. Check that the .env file is in .gitignore.

Show me the plan before making any changes.

1. Request a password reset email from your app to yourself.
2. Check the Emails (sending logs) section in Resend. The email should show Delivered.
3. Open the email in Gmail. From the ⋮ menu in the top right, choose Show original.
4. SPF, DKIM and DMARC should all say PASS.
5. The sender should be on your new domain (notifications@yourdomain.com), not your old mail account.

• If everything runs smoothly for a few days, revoke the old SMTP credentials (app password, etc.). An unused password is an open door.
• As volume grows, keep an eye on your plan's daily and monthly limits.
• Hook up webhooks for bounced and complained (marked as spam) events. Repeatedly emailing an invalid address hurts your domain's reputation; remove those addresses from your list.