How to send email from Cloudflare Workers

You generally can’t send raw SMTP email directly from Cloudflare Workers because Workers run in a serverless, edge environment and don’t support opening arbitrary TCP sockets to SMTP servers.

Common ways to send email from a Worker

1) Use an email API provider

This is the most common approach.

Popular options:

• Resend
• SendGrid
• Mailgun
• Postmark
• Amazon SES via HTTP API

In your Worker, call their HTTPS API with fetch().

Example with a generic HTTP email API:

export default {
  async fetch(request, env) {
    const res = await fetch("https://api.example.com/send-email", {
      method: "POST",
      headers: {
        "Authorization": `Bearer ${env.EMAIL_API_KEY}`,
        "Content-Type": "application/json",
      },
      body: JSON.stringify({
        from: "no-reply@yourdomain.com",
        to: "user@example.com",
        subject: "Hello from Cloudflare Workers",
        text: "This was sent from a Worker!",
      }),
    });

    return new Response(await res.text(), { status: res.status });
  }
}

Store the API key as a Worker secret:

wrangler secret put EMAIL_API_KEY

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2) Use Cloudflare Email Routing + a backend

Cloudflare Email Routing receives mail, but it’s not for sending mail from Workers. If you need outgoing mail, pair Workers with an external mail service.

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3) Use an email service through an SMTP relay outside Workers

If you must use SMTP, run a small backend somewhere else that your Worker calls over HTTPS, and that backend sends the SMTP email.

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Best practice

For Workers, the best pattern is:

Worker → HTTPS email API → email delivered

This is simple, secure, and works well in serverless environments.

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Important notes

• Don’t put API keys directly in your code.
• Verify sender domains with your email provider.
• Be aware of rate limits and anti-spam rules.

If you want, I can give you a complete Cloudflare Worker example using Resend, SendGrid, or Postmark.