Resend.com Emails using Cloudflare Workers

Send transactional emails from your Cloudflare Workers using Resend.com. Perfect for contact forms.

Table of Contents

• Prerequisites
• Getting Started
• Environment Variables
• Usage
  • Sending Emails
  • Encrypting Emails
• Changing the Sender Username
• Adding Cloudflare Turnstile captcha

Prerequisites

1. Add your domain to Resend.com: Follow the instructions on the Resend.com dashboard to add your domain.
2. Generate Resend.com API key: Create a new API key with Sending access permission. This will be used to authenticate your emails.

Getting Started

Quick Deployment

Manual Deployment

1. Install dependencies: Run npm install to install the required dependencies.
2. Run the setup script: Run ./cli.js and follow the instructions.

This will create a .dev.vars file with your RESEND_CONFIG and SALT values.

3. Set environment variables: Use the created RESEND_CONFIG and SALT values and run:

   • npx wrangler secret put RESEND_CONFIG
   • npx wrangler secret put SALT

   (Alternatively, you can set these values via your Cloudflare Dashboard.)

4. Deploy the Cloudflare Worker: Run npm run deploy to deploy the Cloudflare Worker.

Environment Variables

The following environment variables are used in this project:

• RESEND_CONFIG*: includes:
  • API key from Resend.com (api_key)
  • Domain name used in Resend.com setup (domain)
  • Custom profile name (profile) (used in request 'profile' header or path param)

Multiple configs supported via | separator

Optional

• SALT: a random value used for recipient email encryption (if you want to obfuscate your email address)
• ENCRYPT_EMAIL_PATH: URL path suffix for email encryption (if you wish to expose the email encryption URL to live environment)
• CAPTCHA_SECRETS: Cloudflare Turnstile captcha secrets keys (if you need captcha validation before sending email)

Usage

This section covers how to use the Cloudflare Worker to send emails through Resend.com and how to encrypt email addresses for added security.

Sending Emails

To send an email, make a request to the Cloudflare Worker with the required parameters. The worker handles the email sending process using Resend.com, based on the Resend.com - [POST] Send Email endpoint.

Request Payload

[POST] /send/:profile OR [POST] /send with the profile header

Content type: application/json and application/x-www-form-urlencoded are supported.

Required payload values:

• recipient: string | string[] - The recipient email address. Max 50. e.g. "yourpersonalemail@gmail.com" (this can be the encrypted email or plain email)
• email: string | string[] - The reply-to email address. e.g. "john.smith@example.com"
• html: string - The HTML version of the message

Optional values:

• name: string - The sender label, e.g. "John Smith".
• subject: string - The email subject.
• bcc: string | string[] - The Bcc recipient email address.
• cc: string | string[] - The Cc recipient email address.
• scheduled_at: string - Schedule email to be sent later. The date should be in ISO 8601 format (e.g: 2024-08-05T11:52:01.858Z).
• text: string - The plain text version of the message.
• headers: object - Custom headers to add to the email.
• attachments: object[] - Filename and content of attachments (max 40mb per email) (example).
• tags: object[] - Custom data passed in key/value pairs (example).
• Any key starting with : will be appended to the html message as additional content.

Example Request

[POST] /send/main

{
  "recipient": "john.smith@example.com",
  "name": "John Smith",
  "email": "john@gmail.com",
  "html": "<p>My sample message from API</p>",
  "subject": "What is love?",
  ":Favourite pet": "Dragon",
  ":Favourite Colour": "Orange"
}

Bruno collection available in bruno folder.

Note: From Resend.com the react, from, to, reply_to parameters are not supported.

Examples

Examples can be found in the examples folder.

Search Parameters

Optional parameters:

• includeMeta: Should collect information about the sender, such as userAgent, Location, IP address etc (default: true)
• preventThreading: Should prevent threading e.g. in Gmail (default: true)

Encrypting Emails

For added security, you can encrypt the recipient email address before including it in the payload. Either:

Locally

Run your worker locally and use the encrypt endpoint:

npm run start

Then navigate to http://localhost:8787/encrypt?email=johndoe@example.com

Live

Set ENCRYPT_EMAIL_PATH as your environment variable and navigate to https://yourworkerurl.com/encrypt/${ENCRYPT_EMAIL_PATH}?email=johndoe@example.com

Changing the Sender Name/Label

By default, the sender username is set to submissions-noreply, which translates to the sender being submissions-noreply@yourdomain.com. If you wish to change this, you can edit the EMAIL_SENDER_USERNAME value in wrangler.toml and deploy, or set it via your Cloudflare Dashboard.

Adding Cloudflare Turnstile captcha

Follow the Get started with Turnstile guide and use the turnstile sitekey in CAPTCHA_SECRETS environment variable. For example: profile=main&key=1x0000000000000000000000000000000AA

Roadmap

• Add configurable CORS policies