How do I send emails from a Cloudflare Worker?

Cloudflare Workers can send email, but not directly through SMTP sockets. Workers run in a serverless, no-long-lived-connection environment, so the usual pattern is:

1. Call an email API over HTTPS, or
2. Use Cloudflare’s email-related products (depending on your use case), or
3. Forward to your own backend that sends email.

Common options

1) Use an email provider’s HTTP API

This is the easiest and most common approach.

Examples:

• SendGrid
• Mailgun
• Postmark
• Resend
• Amazon SES (via API, not SMTP)

Your Worker makes a fetch() request to the provider’s API endpoint.

Example with a generic HTTP email API

export default {
  async fetch(request, env) {
    const res = await fetch("https://api.emailprovider.com/send", {
      method: "POST",
      headers: {
        "Authorization": `Bearer ${env.EMAIL_API_KEY}`,
        "Content-Type": "application/json",
      },
      body: JSON.stringify({
        from: "you@example.com",
        to: "recipient@example.com",
        subject: "Hello from Cloudflare Workers",
        text: "This email was sent from a Worker.",
      }),
    });

    if (!res.ok) {
      return new Response(`Email send failed: ${await res.text()}`, { status: 500 });
    }

    return new Response("Email sent");
  }
};

Store the API key as a secret:

wrangler secret put EMAIL_API_KEY

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2) Use Cloudflare Email Routing + Worker integration

If your goal is to receive and process inbound email, Cloudflare has built-in email handling via Email Routing and Workers.
That’s for incoming mail, not directly for sending outbound messages.

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3) Use a backend service

If you already have an app server, your Worker can call your backend, and your backend handles SMTP or an email API.

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Important limitations

• Workers cannot open raw SMTP connections
• Workers are best suited for HTTP-based email sending
• Keep secrets in Worker secrets, not in code
• If sending user-triggered email, add rate limiting / abuse protection

Recommended approach

If you want to send transactional emails from a Worker, use:

• Resend or Postmark for simplicity, or
• SendGrid/Mailgun if you already use them.

If you want, I can show you a complete Worker example using Resend, SendGrid, or Mailgun.